Showing papers in "The Auk in 1986"

A Fixed-Radius Point Count Method for Nonbreeding and Breeding-Season Use

Abstract: -We provide a detailed description of a fixed-radius point count method that carries fewer assumptions than most of the currently popular methods of estimating bird density and that can be used during both the nonbreeding and breeding seasons. The method results in three indices of bird abundance, any of which can be used to test for differences in community composition among sites, or for differences in the abundance of a given bird species among sites. These indices are (1) the mean number of detections within 25 m of the observer, (2) the frequency of detections within 25 m of the observer, and (3) the frequency of detections regardless of distance from the observer. The overall ranking of species abundances from a site is similar among the three indices, but discrepancies occur with either rare species that are highly detectable at great distances or common species that are repulsed by, or inconspicuous when near, the observer. We argue that differences in the behavior among species will preclude an accurate ranking of species by abundance through use of this or any other counting method in current use. Received 3 September 1985, accepted 2 February

A phylogenetic analysis of recent anseriform genera using morphological characters

Abstract: --A phylogenetic analysis of all Recent genera of the Anseriformes using 120 morphological characters supports much of the current consensus regarding intraordinal relationships. I found that (1) Anseranas hould be placed in a monotypic family; (2) Dendrocygna, Thalassornis, geese and swans, and Stictonetta re paraphyletic to the rest of the Anatidae; (3) Cereopsis the sister group to Anser and Branta, and Coscoroba is the sister group to Cygnus and Olor; (4) Plectropterus i the sister group to the Tadorninae (shelducks) and the Anatinae (typical ducks); (5) the shelducks are monophyletic and include Sarkidiornis (provisionally), Malacorhynchus, Hymenolaimus, Merganetta, and Tachyeres; (6) the tribe \"Cairinini\" (\"perching ducks\") is an unnatural, polyphyletic assemblage and is rejected; (7) the dabbling ducks (including the smaller \"perching ducks\") comprise an unresolved, probably paraphyletic group; (8) tribal monophyly of the pochards (including Marmaronetta nd Rhodonessa), sea ducks (including the eiders), and stiff-tailed ducks (including Heteronetta) is confirmed; and (9) the retention of Mergellus and resurrection of Noraonyx are recommended based on clarifications of intratribal relationships. Problematic groups, effects of homoplasy, phenetic comparisons, life-history correlates, biogeographic patterns, and fossil species are discussed, and a phylogenetic classification of Recent genera is proposed. Received 18 November 1985, accepted 2 April 1986. THE order Anseriformes is considered to comprise the families Anhimidae (2 genera, 3 species) and Anatidae (approximately 43 genera and 150 species). The family Anatidae is undoubtedly one of the best-studied groups of birds, owing largely to the historical importance of waterfowl for hunting (Weller 1964a), domestication (Delacour 1964a), and aviculture (Delacour 1964b). The classification of the Anatidae proposed by Delacour and Mayr (1945) has been followed, with only minor revisions, in recent decades (e.g. Delacour 1954, 1956, 1959, 1964c; Johnsgard 1961a, 1962, 1965a, 1978, 1979; Woolfenden 1961; Frith 1967; Bellrose 1976; Palmer 1976; A.O.U. 1983; Bottjer 1983; Scott 1985). Perhaps the most innovative aspect of this system (inspired by the works of Salvadori 1895; Phillips 1922, 1923, 1925; and Peters 1931) was the erection of \"tribes,\" groups of genera that were considered to be closely related within the subfamilies of the Anatidae. These tribes became the primary focus of subsequent works on anatid classification, many of which addressed the tribal assignments of problematic genera (e.g. Humphrey and Butsch 1958; Johnsgard 1960a, 1961b; Humphrey and Ripley 1962; Davies and Frith 1964; Raikow 1971; Kear and Murton 1973). Most authors assumed the validity of the tribes and used them as working units in phylogenetic analyses of the family (e.g. Johnsgard 1961a, Bottjer 1983). A few workers named additional tribes (Moynihan 1958, Delacour 1959, Woolfenden 1961, Weller 1968b) or attempted to test the naturalness of those originally proposed (Cotter 1957, Woolfenden 1961, Brush 1976). Behavioral characters have been accorded considerable weight in classifications of waterfowl. Delacour and Mayr (1945) based their revision on characters they considered to be \"non-adaptive,\" including behavioral displays, nesting and feeding habits, and selected morphological characters (e.g. posture, body proportions, head shape, syringeal bulla). Reliance on comparative ethology in anatid systematics was furthered by the studies of Lorenz (19511953), McKinney (1953), and Myres (1959) and was increased significantly by Johnsgard (1960a-c, 1961a-d, 1962, 1964, 1965a, b, 1966a, b, 1967, 1978), whose work was largely ethological and influenced profoundly by that of Delacour (1954, 1956, 1959, 1964c). This emphasis, work on interspecific hybridization 737 The Auk 103: 737-754. October 1986 738 BRADLEY C. LIVEZEY [Auk, Vol. 103 (Sibley 1957; Gray 1958; Johnsgard 1960d, 1963), and study of plumage patterns of downy young (Delacour 1954, 1956, 1959; Frith 1955, 1964b; Kear 1967) were prompted in part by the opportunity to observe waterfowl in avicultural collections. Other data used in the classification of waterfowl include syringeal anatomy (Humphrey 1955, 1958; Johnsgard 1961e), cytogenetics (Yamashina 1952), serology (Cotter 1957, Bottjer 1983), osteology (DeMay 1940, Verheyen 1955, Humphrey and Butsch 1958, Woolfenden 1961, Humphrey and Ripley 1962, Raikow 1971), feather lice (Timmermann 1963), eggshell structure (Tyler 1964), egg-white proteins (Sibley 1960, Sibley and Ahlquist 1972), feather proteins (Brush 1976), royology (Zusi and Bentz 1978), lipids from the uropygial gland (Jacob and Glaser 1975, Jacob 1982), and mitochondrial DNA (Kessler and Avise 1984). These studies, with the possible exceptions of those by Lorenz (1953) and Kessler and Avise (1984), estimated the evolutionary relationships of groups by assessments of overall similarities; no attempts were made to determine primitive conditions or to distinguish shared primitive characters from shared derived characters (\"special\" similarity). Moreover, the \"evolutionary trees\" presented in most of these works lack references to the specific characters used to support the branching patterns (e.g. Delacour and Mayr 1945; Johnsgard 1961a, 1978; Woolfenden 1961). I performed a phylogenetic (cladistic) analysis of Recent genera of Anseriformes using 120 morphological characters. I present a hypothetical evolutionary tree for the order, consider the taxonomic implications, and discuss selected life-history and biogeographic correlates and the classification of selected fossil species. Many of the characters were described first in the pioneering work of Woolfenden (1961), to whom I dedicate this paper.

Influence of Resource Abundance on Use of Tree-Fall Gaps by Birds in an Isolated Woodlot

Abstract: ABSTR^CT.--The occurrence of birds in forest understory and tree-fall gaps during spring and fall migration periods was determined in an isolated woodlot. We used mist-net captures to test the hypothesis that birds are attracted to gaps because of higher resource levels. We captured 1,010 birds (74 species) in spring and 458 (44 species) in fall. Total captures and captures per net were higher (P < 0.001) in gaps during spring and fall. Mean number of species per net was higher in gaps (P < 0.001) during both seasons, but total species in gaps (69 spring, 43 fall) was not significantly higher than in forest understory (60 spring, 28 fall). Of 44 species represented by adequate sample sizes (n > 5) in spring, 9 were significantly (P < 0.05) more common in gaps and 2 were more common in forest understory. Nine of 17 species were captured more often (P < 0.05) in gaps during fall. During spring, flycatchers, ground insectivores, foliage insectivores, and granivore-omnivores were captured more frequently (P < 0.05) in gaps. Flycatchers howed no difference in fall, but other trophic groups, including frugivores, were captured more frequently (P < 0.05) in gaps than in forest understory sites. Bark foragers showed no statistical preference for gaps or forest understory in spring or fall. Total species per net and total captures per net correlated positively (P < 0.05) with density of foliage in the lower canopy and negatively with density of upper canopy foliage in both spring and fall. Total species and captures correlated positively (P < 0.05) with insect abundance in spring and with fruit abundance in fall. Foliage insectivores correlated positively with low canopy foliage and insect abundance in both spring and fall. Captures of frugivores correlated with fruit abundance in fall. These data support the hypothesis that birds are attracted to tree-fall gaps because of higher resource abundance and provide further evidence of the importance of habitat heterogeneity to the structure and composition of bird communities. Received 7 November 1984, accepted 28 October 1985.

Why Does Intensity of Avian Nest Defense Increase During the Nesting Cycle

Abstract: -Theoretical models predict that intensity of avian nest defense should increase with age of the offspring. Empirical observations conforming with this prediction have been taken as support for these models. We here present a new explanation for the observed correlations between offspring age and level of nest defense. We propose that increased intensity of nest-defense behavior is largely a result of the methods used by the researchers who made the observations. We suggest that when an observer repeatedly visits or brings a potential nest predator to a nest, nest-defense behavior of parents is modified by positive reinforcement and loss of fear. We tested this hypothesis by measuring nest-defense behavior of female American Robins (Turdus migratorius) and male and female Red-winged Blackbirds (Agelaius phoeniceus). The tests were performed at nests visited only once during different stages of the nesting cycle and at a group of nests visited repeatedly from initiation of incubation to fledging. Nest-defense intensity (as measured by call rates, closest approach to the predator, and numbers of dives and strikes) of robins and blackbirds at nests visited once, in most cases, did not increase through the nesting cycle. At nests visited repeatedly through the nesting cycle, intensity of nest defense by both robins and blackbirds, in many cases, increased significantly. In addition to intensity of nest defense increasing at multiplevisit nests, we observed higher proportions of birds at these nests performing nest-defense behaviors than at single-visit nests. Received 19 March 1985, accepted 20 October 1985. MOST studies of nest defense in altricial birds have revealed increases in the intensity of nest defense by parent birds through the nesting cycle (Smith 1950; Erpino 1968; Barash 1975; Curio 1975; D'Arms 1978; Weatherhead 1979, 1982; Andersson et al. 1980; Greig-Smith 1980; Patterson et al. 1980; Biermann and Robertson 1981; East 1981; Blancher and Robertson 1982; R6ell and Bossema 1982; Merritt 1984; Shields 1984). Two explanations have been offered for the temporal changes in the intensity of nest defense. The first, and currently most popular, explanation is derived from the theory of parental investment (Trivers 1972). Barash (1975) extended the theory to include parental defense of eggs and young. Whether based on cumulative past parental investment (Trivers 1972, Barash 1975) or future expected benefits minus expected costs (Dawkins and Carlisle 1976, Boucher 1977, Maynard Smith 1977), this hypothesis predicts an increase in nest defense as the young near fledging. In a similar fashion, Andersson et al. (1980) hypothesized that the relative difference between the expected 1 Present address: Institute for Environmental Studies, University of Washington, Seattle, Washington 98195 USA. survival of parents and their young decreases as the nestlings grow older, making parents willing to defend older nestlings more aggressively. The second explanation is based on the hypothesis that older nestlings are more conspicuous to predators. The nest and its contents become more conspicuous as the nesting cycle progresses, necessitating an increase in the intensity of nest defense to counteract the nest's increased conspicuousness to predators (Skutch 1949, Harvey and Greenwood 1978). We offer a third, alternative explanation for increases in nest defense through the nesting cycle. We propose that the increases are largely the results of the methods used by the researchers who made the observations. We suggest that when an observer repeatedly visits or brings a potential predator to a nest and records the parent birds' responses, the nest-defense behavior is gradually modified by positive reinforcement and loss of fear. Positive reinforcement is involved because the parent birds have been rewarded repeatedly for their nest-defense behavior. After being attacked, the observer or other potential nest predator leaves without harming the nest. A loss of fear is involved because the defending birds gradually 318 The Auk 103: 318-327. April 1986 This content downloaded from 157.55.39.49 on Mon, 29 Aug 2016 05:19:04 UTC All use subject to http://about.jstor.org/terms April 1986] Changes in Nest-defense Intensity 319 learn that the observer or other potential nest predator is not dangerous to them; however, they still view the object as a threat to the nest's contents. Both positive reinforcement and loss of fear could explain much of the reported increases in nest-defense behavior. We examined these explanations by measuring nest-defense behavior in experiments with American Robins (Turdus migratorius) and Redwinged Blackbirds (Agelaius phoeniceus). STUDY AREA AND METHODS Nests of blackbirds and robins were located within the city of Madison, Wisconsin. Some nests were visited every 3 days, whereas others were visited only once. Blackbird nests visited once were located in Nielsen, University Bay, Redwing, and Odana marshes; nests visited repeatedly were located in Kettle Marsh. These areas are open water, cattail (Typha spp.) marshes (Bedford et al. 1975). At no time during the study period were humans seen in any of these marshes. All robin nests were located on the University of Wisconsin campus and adjacent neigh-

Differential Timing of Spring Migration in Wood Warblers (Parulinae)

Abstract: -Spring migration patterns of 18 species of paruline warbler at Prince Edward Point, Ontario showed that males arrived earlier than females in all species. Adult males arrived significantly earlier than second-year males in American Redstarts (Setophaga ruticilla), and there was evidence for a similar trend in other species. The difference in mean arrival dates between the sexes was greatest in species that arrived earliest. Similarly, within species, the difference between sexes was greatest in years when the males arrived earliest. For individuals within a species there was a significant negative correlation between arrival date and wing length; however, males of a particular size generally arrived earlier than females of the same size. Thus, larger size may be an advantage to early arrival, but is not sufficient to explain the difference in arrival between sexes. Species that winter furthest north arrived earliest, but sexual differences in wintering grounds have not been reported. These results are consistent with the hypothesis that males are selected to arrive as early as food resources or climatic conditions are adequate, whereas females arrive later, closer to the time when they can successfully begin nesting. Received 19 August 1985, accepted 11

Food Passage and Intestinal Nutrient Absorption in Hummingbirds

Abstract: Etude de l'adaptation de la physiologie digestive permettant a Selasphorus rufus et Calypte anna d'absorption des aliments sucres rapidement et efficacement

The relationship between body mass and survival of wintering canvasbacks

Abstract: -Mass and recapture histories of 6,000 Canvasbacks (Aythya valisineria) banded in upper Chesapeake Bay were used to test two hypotheses: (1) early-winter body mass is associated with the probability of surviving the winter, and (2) early-winter body mass is associated with annual survival probability. Data were analyzed by a binary regression method that treated mass as a continuous variable and estimated parameters to describe a general relationship between body mass and survival probability. Results for adult males, which provided our largest data sets, presented strong evidence that birds with high relative earlywinter masses had both greater overwinter and annual survival probabilities. Results of overwinter analyses necessarily are qualified by the alternative explanation of mass-dependent emigration, i.e. the possibility that lighter birds move south in response to cold weather and leave only heavy birds for recapture. Such a phenomenon remains to be documented. Results concerning annual survival probabilities are not vulnerable to this alternative explanation because of the strong fidelity of Canvasbacks at the banding site. Because of small sample size, data were inadequate to permit mass/survival inferences for adult females. Sample sizes were adequate for young Canvasbacks, but the results were less consistent than for adult males. Although early-winter body mass was associated positively with overwinter as well as annual survival for young Canvasbacks in some years, we suspect that the lack of established wintering patterns among these birds may underlie the less consistent result. Received 11 February 1985, accepted 9 January 1986. FOR several species of waterfowl, evidence now exists for a relationship between the physiological state or "condition" of an individual and its subsequent reproductive performance (e.g. Ankney and MacInnes 1978; Raveling 1979; Krapu 1979, 1981). It is also reasonable to expect that the "physiological condition" of an individual at some time t is related to its probability of surviving some subsequent period (t, t + A), especially if the period is one in which food resources are limited or environmental conditions are energetically stressful, or both. This expectation has been accepted in the literature not only for waterfowl, but for birds and mammals in general, and it is now a tacit assumption of most published studies dealing with physiological condition during nonbreeding periods. We are aware of few efforts that use birds, however, to test the hypothesis that particular physiological characteristics are related to survival probability. There is considerable speculation and some evidence for several bird species that food supplies may be limited during winter and that both food availability and winter weather are related to survival probability (Lack 1966; Fretwell 1968, 1972; Goss-Custard 1979; North and Morgan 1979; Pulliam and Parker 1979; van Balen 1980; Ekman et al. 1981; Jansson et al. 1981). Winter is thus a logical time to look for a relationship between physiological condition and survival within many Temperate Zone birds. Two general approaches have been used to draw inferences about the relationship between condition and survival in wintering birds. The first involves comparisons of variables believed to reflect condition (e.g. body mass, percentage of fat or lipid in the body, percentage of protein in the body) between two groups: (1) birds found dead during periods of severe winter weather, and (2) birds collected during "normal" or mild winter weather and believed to be representative of live wintering birds. There are large differences between these two groups for Eurasian Coots (Fulica atra; Visser 1978), Common Redshanks (Tringa totanus; Davidson and Evans 1982), and Eurasian Oystercatchers (Haematopus ostralegus; Davidson and Evans 1982, Swennen and Duiven 1983). Thus, these results provided evidence that lipid and 506 The Auk 103: 506-514. July 1986 This content downloaded from 157.55.39.100 on Thu, 25 Aug 2016 04:57:15 UTC All use subject to http://about.jstor.org/terms July 1986] Canvasback Mass and Survival 507 protein reserves are mobilized during periods of severe weather and may be important to winter survival. Nevertheless, these studies did not demonstrate that variation in survival probability is associated with variation in body mass or nutrient reserves. The second general approach permits stronger inferences about this relationship. Birds are captured and weighed (or assigned to a condition category by some other means) at the beginning of a winter period. Recaptures or resightings of the birds at the end of the period are then used to draw inferences about variation in survival probabilities for birds of different masses or condition categories. We are aware of two such studies on wintering birds. In a 2-yr study, Fretwell (1968) captured and banded 85 Field Sparrows (Spizella pusilla) in early winter and assigned them to two fat categories (above and below average). The proportion of birds seen later in winter was significantly greater for the above-average category in 1 of 2 years. In another study, Kikkawa (1980) weighed and color-banded 388 first-year Gray-backed White-eyes (Zosterops lateralis) at the beginning of winter over a 3-yr period. Resightings at the end of each winter showed no significant difference between the proportion of birds above vs. below average in initial mass. We use an approach similar to the second described above with Canvasbacks (Aythya valisineria) wintering on Chesapeake Bay. Winter weather conditions on Chesapeake Bay are frequently subfreezing, and prolonged ice cover may limit food availability for Canvasbacks. In addition, resource-related differences in winter mortality associated with behavioral dominance or fasting endurance may be important selective forces in the evolution of winter distribution patterns in this species (Nichols and Haramis 1980, Alexander 1983, Haramis et al. 1985). In ducks, there is generally a good correlation between body mass and both fat (Owen and Cook 1977, Bailey 1979) and total nutrient (lipid + protein) reserves (Wishart 1979). Therefore, we expect high body masses to reflect good reserves and possibly confer a greater probability of surviving the winter. In our study, masses and recapture histories of Canvasbacks were used to test two hypotheses: (1) Canvasback body mass in early winter is associated with the probability of surviving that winter, and (2) Canvasback body mass in early winter is associated with subsequent annual survival probability.

Reproductive Performance of Seabirds: The Importance of Population and Colony Size

Abstract: We compared reproductive performance of five species of seabirds at two colonies, St. George Island (2.5 million birds) and St. Paul Island (250,000 birds), in the southeastern Bering Sea. All species had lower chick growth rates at the larger colony, and the differences were statistically significant in four species. Fledge weights of Common Murres (Uria aalge) on St. George Island were 84-88% of those on St. Paul. Average fledge weights of Thick-billed Murres (Uria lomvia) on St. George were only 74% of those for chicks from St. Paul. We found no significant differences in clutch size or breeding success between populations breeding at the two colonies. For three species, Black-legged Kittiwakes (Rissa tridactyla), Common Murres, and Thick-billed Murres, we extended our analysis to include published data from other colonies. We examined breeding performance as a function of colony size, population size (suggestive of intraspecific competition), and "effective colony size," the sum of the populations of species with considerable dietary overlap (suggestive of interspecific competition for food). We found consistently negative relationships between population size and several measures of breeding performance (clutch size, growth rate, fledge weight, and breeding success). In addition to the lower breeding success at colonies that support large populations, chicks from these colonies may be subject to higher postfledg- ing mortality because of fledging at lower weights. Received 7 January 1985, accepted 18 October 1985.

Sources of Variation in Growth of Tree Swallows

Abstract: We studied two populations of Tree Swallows (Tachycineta bicolor) that differed primarily in the amount of food available to the breeding birds. We obtained an index of food abundance and performed field experiments to distinguish factors affecting variability in growth of nestlings. The experiments were designed to detect the influence of the location of egg laying, incubation, and nestling rearing, type of parent (natural or foster), and year of breeding on nestling growth. Some broods were transferred between nests and raised by foster parents, and some clutches and broods were transferred between populations. Vari- ables were analyzed in two- and three-way factorial analyses of variance. The insect biomass index during the nestling period differed about 7-fold between loca- tions, regardless of year of breeding. Nestlings with more food grew and survived better. Type of parent (i.e. natural or foster) or prehatch factors such as location of incubation did not influence growth. The location where nestlings were raised, however, explained as much as 51% of the variation in growth, and genetic variation in offspring and variation in pro- visioning abilities of parents may have been important components of within-population variation in growth regardless of where parents nested. Received 11 February 1985, accepted 25 November 1985. THE main selective pressures responsible for reproductive performance in nidicolous birds are the availability of food, especially for the young and to a lesser extent for the laying fe- male, and the risk of predation on eggs, young, and parents (Lack 1968). Implicit in Lack's hy- pothesis is a limitation due to parental foraging ability. Nestling growth or survival has been shown (usually indirectly) to be affected by food supply in several bird species (van Balen 1973; von Bromssen and Jansson 1980; Bryant 1975, 1978a; Crossner 1977; Bryant and Gardiner 1979; Ross 1980; Prince and Ricketts 1981). Reduced availability of food markedly affects parental feeding success in some species (Dunn 1973, Bovino and Burtt 1979, Quinney and Smith 1980), and parents that raise large broods may show reduced survival or body mass compared with those that raise smaller broods (Hussell 1972, Askenmo 1977, Tinbergen 1981). Previously, the role of food abundance in re- production often has been obscured because adequate measurements of food supply are dif- ficult to obtain and because of the difficulties

Trophic Organization of Understory Birds in a Malaysian Dipterocarp Forest

Abstract: -Single-sample studies suggested that understory flowers and fruits and their avian consumers are scarce in the Malaysian rain forest as compared with African and Central American rain forests. Results from my longer-term studies at Pasoh Forest Reserve (Negeri Sembilan, Peninsular Malaysia) established that flowers and fruits were consistently rare as food for birds. A comparison of two forest types at Pasoh revealed the effect of lower food availability on avian trophic organization. Food resources (e.g. flowers, fruits, arthropods) were less abundant in the regenerating than in the virgin forest, and bird species richness and individual abundance were also lower in the regenerating forest understory. However, the two forests did not differ significantly in the relative importance of the various foraging guilds, suggesting that similar types of resources were present in similar proportions. None of the birds sampled in the Malaysian rain-forest understory was a specialized consumer of understory flowers or fruit, whereas birds feeding mainly on foliage-dwelling arthropods were abundant and were represented by many species. This trophic organization is contrary to that reported for rain forests in other tropical regions but may simply reflect an allocation of harvestable productivity that is different rather than lower. Received 16 January 1985, accepted 23 July 1985. THE absence of avian frugivores in short-term mist-net samples from the Malaysian rain-forest understory (Karr 1980) hinted at a departure from the trophic organization observed in similar short-term studies in African and Central American rain forests, where frugivorous birds comprised 25-33% of mist-net captures (Karr 1980). Similar short-term work prompted Janzen (1977) to comment on the unusually low density of plants flowering or fruiting in the Malaysian rain-forest understory as compared with similar vegetation in Costa Rica. Janzen (1977) independently suggested that frugivores were not likely to be an important component of the Malaysian understory fauna because there would be little for them to eat. However, such observations of low frugivore density and low reproductive activity of plants based on single visits can arise from one of two rather different ecological situations. Reproductive activity of understory plants and frugivore density may indeed be consistently low. Alternatively, frugivores may have been absent temporarily from the area because the lo' Present address: Smithsonian Tropical Research Institute, P.O. Box 2072, Balboa, Republic of Panama. cal availability of seasonally abundant flowers and fruits was low during the short sampling period. Certain attributes of the Malaysian rain forest promote the expectation that understory flowers and fruits, and their consumers, are consistently low in abundance. The tree family Dipterocarpaceae dominates the canopy of the Malaysian rain forest. A compilation of surveys covering 7,900 acres of lowland and hill forest in peninsular Malaysia revealed that dipterocarps comprise 30% of the trees ('30 cm in diameter) by number and 55.5% by volume (Symington 1974). In a given forest, there may be 10-40 dipterocarp species (Symington 1974) that reproduce synchronously at irregular intervals of 2-8 yr (Burgess 1972, Medway 1972, Janzen 1974, Ng 1977). Many tree species from other families (e.g. Bombacaceae, Guttiferae, Sapindaceae) also follow this reproductive cycle and either will only fruit or will fruit more heavily during dipterocarp mast years (Whitmore 1984). Although as yet undocumented, the amount of harvestable productivity (the portion of primary productivity that goes into the production of flowers, fruits, and new leaves and that is consumable by animals) in the canopy of dipterocarp forests must vary in accordance 100 The Auk 103: 100-116. January 1986 This content downloaded from 157.55.39.235 on Fri, 07 Oct 2016 06:28:28 UTC All use subject to http://about.jstor.org/terms January 1986] Birds in Malaysian Forest Understory 101 PASOH FOREST RESERVE

Moonlight avoidance behavior in Leach's Storm-Petrels as a defense against Slaty-backed Gulls

Abstract: -Diurnal activity patterns of Leach's Storm-Petrels (Oceanodroma leucorhoa) and Slaty-backed Gulls (Larus schistisagus) were investigated. The petrels reduced activity in moonlight in May and June when the predation rate by gulls was relatively high. Petrel activity levels were inversely correlated with light intensities and the corresponding risk of predation by the gull. This suggests that nocturnal activity and moonlight avoidance by the petrel in its colony are an effective defense against diurnal predators. Activity synchronization of the petrel was most marked during the full moon, further supporting the predatoravoidance hypothesis. Received 15 October 1984, accepted 27 April 1985. MANX Shearwater (Puffinus puffinus; Harris 1966), Leach's Storm-Petrel (Oceanodroma leucorhoa; Harris 1974), Fork-tailed Storm-Petrel (0. furcata; Harris 1974, Boersma et al. 1980), and Cassin's Auklet (Ptychoramphus aleuticus; Thoresen 1964, Manuwal 1974) are strictly nocturnal in their colonies and are less active on moonlit nights than on dark nights. Cody (1973) discussed the nocturnal activity of alcids as a defense against diurnal predators. Gross (1935), M. P. Harris (1966), and S. W. Harris (1974) also suggested that nocturnal procellariiforms are vulnerable to diurnal predatory gulls on moonlit nights. However, the relationship between daily activities of procellariiforms and predation risk has not been studied. I studied Leach's Storm-Petrels and Slatybacked Gulls (Larus schistisagus) on Daikoku Island. Their activity patterns are described and the nocturnal behavior of the petrels in the colony is discussed as predator avoidance. STUDY AREA AND METHODS The colony.-The study was conducted on Daikoku Island (42?52'N, 144?52'E), Akkeshi, Hokkaido, between late April and early October 1982. The island is 6.1 km in circumference and treeless, with the exception of birch (Betula ermanii) groves in the ravines. Leach's Storm-Petrel (the only petrel breeding on the island) nests in the interior parts of the island, which is covered with Artemisa montana and Urtica platyphilla. Abe et al. (1972) estimated that there were 1,070,000 breeding pairs of petrels, but a more recent estimate is 415,000 (Watanuki 1985b). About 3,500 pairs of Slaty-backed Gulls nested on maritime slopes, which are covered with Calamagrostis langsdorffii, isolated rock stacks, and cliff ledges. A few pairs of Blacktailed Gulls (L. crassirostris) nested on these sites. The Slaty-backed Gull is an important predator of adult petrels on the island. Although Jungle Crows (Corvus macrorhynchos) excavated petrel burrows and ate adults, eggs, and chicks, predation by the small crow population (13 pairs) was not significant. Activity patterns.-Observations of flying birds were made from a blind set on top of a headland about 25 m above sea level. For 5 min every 30 min, I counted all birds passing an imaginary 20 x 30-m plane oriented vertically with reference to the cliff face opposite the headland. Two 6-volt electric lights, one set horizontally and the other about 450 upward at the blind, lit the plane facing toward the sea from the lower corner to the opposite side. This reduced the effect of the light on landing birds approaching from the sea. If all the landing petrels were attracted instantaneously to the lights, the number of petrels flying through the lights would increase during the observations. However, the number was rather constant during 5-min observations (Fig. 1). A few petrels and gulls flew circularly in the lights; these were excluded from the data. Observations on moonlit nights showed that Slaty-backed Gulls did not avoid the lights. No differential response to the lights by gulls and petrels was assumed. Observations started in daylight and lasted 24 h (n = 19 days). Data taken during a day with dense fog (13-14 May) were excluded from the analysis because of low visibility. Data of 27-28 April were included in those of May. Light intensity was measured by a lux-meter (? 10%) set horizontally and was divided into four classes: dark (0 lux), moonlight with no cloud cover ( 5 x 104 lux). Time of sunrise, sunset, moonrise, and moonset were from the astronomical tables for Kushiro, about 40 km west of Daikoku Island. 14 The Auk 103: 14-22. January 1986 This content downloaded from 207.46.13.75 on Fri, 08 Jul 2016 05:57:15 UTC All use subject to http://about.jstor.org/terms January 1986] Moonlight Avoidance in Leach's Petrel 15

Foraging Behavior of Gentoo and Chinstrap Penguins as Determined by New Radiotelemetry Techniques

Abstract: -Analysis of radio signals from transmitters affixed to 7 Gentoo (Pygoscelis papua) and 6 Chinstrap (P. antarctica) penguins allowed us to track penguins at sea. Signal characteristics allowed us to distinguish among 5 foraging behaviors: porpoising, underwater swimming, horizontal diving, vertical diving, and resting or bathing. Gentoo Penguins spent a significantly greater portion of their foraging trips engaged in feeding behaviors than Chinstraps, which spent significantly more time traveling. Gentoos had significantly longer feeding dives than Chinstraps (128 s vs. 91 s) and significantly higher dive-pause ratios (3.4 vs. 2.6). These differences in foraging behavior suggest Gentoo and Chinstrap penguins may have different diving abilities and may forage at different depths. Received 3 June 1985, accepted 24 April 1986. THE trophic relationships among Pygoscelis penguins, the Adelie (P. adeliae), Chinstrap (P. antarctica), and Gentoo (P. papua), have been a major focal point of research in recent years, particularly with respect to the ecology of their major prey species, krill (Euphausia superba). To date, however, our knowledge of the birds' feeding ecology is largely derived from stomach samples obtained ashore (Emison 1968; Croxall and Furse 1980; Croxall and Prince 1980a; Volkman et al. 1980, 1986; Lishman 1985). Diving depth is one aspect of penguin foraging behavior that has been investigated in some detail. Multiple depth recorders, logging the number of dives within set depth ranges, have been deployed on King (Aptenodytes patagonica; Kooyman et al. 1982), Chinstrap (Lishman and Croxall 1983), and Gentoo (Costa pers. comm.) penguins. Maximum diving depths have been reported for Emperor (A. forsteri; Kooyman et al. 1971), Black-footed (Spheniscus demersus; Wilson and Bain 1984), and Gentoo (Adams and Brown 1983) penguins. Feeding range also has been investigated, but indirectly, using nest relief intervals (Williams and Siegfried 1980, Ainley et al. 1984, Croxall et al. 1984). We report a new method of tracking penguins at sea that allowed us to differentiate 1 Present address: National Marine Mammal Laboratory, NOAA/NMFS, 7600 San Point Way N.E., Seattle, Washington 98115 USA. among behaviors during foraging trips. This method improved our understanding of penguin feeding efficiencies, ranges, and traveling speeds, and permitted preliminary comparisons of Gentoo and Chinstrap penguin forag-

Body Size and Condition, Timing of Breeding, and Aspects of Egg Production in Eastern Kingbirds

Abstract: -Variation in timing of breeding in Eastern Kingbirds (Tyrannus tyrannus) was correlated only weakly with external morphological characters, but was correlated positively and significantly with estimates of body size based on measurements of skeletons and muscle weights. Small females apparently held a reproductive advantage in being able to mobilize resources for reproduction before large females. Egg weight was independent of all measures of female size, but was directly and significantly (P = 0.03) correlated with standard flight muscle weight, a relative index of body condition. Egg size was thus a function more of female body condition than size. On average, shell, yolk, and albumen comprised 5.6%, 21.9%, and 72.5%, respectively, of fresh egg weight. Dry albumen and dry shell increased proportionately with fresh egg weight, but dry yolk did not. Total protein, lipid, and energy of fresh eggs all increased proportionately with weight. Comparison of egg composition and standard flight muscle weight of laying females indicated moderate positive, although nonsignificant, correlations between body condition and measures of egg quality, especially lipid content. Based on postegg-laying body composition and nutrient requirements for the production of one egg, it appeared that most females probably could have laid an additional egg almost solely from body reserves. Clutch size thus appears to be independent of body condition. Received 20 June 1985, accepted 16 December 1985. RECENT studies on the evolution of reproductive patterns in birds have emphasized the proximate controls of reproduction, and the bases for phenotypic variation in reproductive traits (Ankney and MacInnes 1978, Drent and Daan 1980, Petrie 1983, Jarvinen and Vaisanen 1984, Murphy et al. 1984). Because intrapopulation variation in timing of breeding is often considerable, and because of the direct influence of size on energy metabolism (Lasiewski and Dawson 1967, Walsberg 1983), various authors have proposed a dependence of breeding date on body size. Small females presumably can divert a greater portion of daily food intake to reproduction, and are predicted to become reproductively active before large females (Wiley 1974, Downhower 1976). Numerous studies (see Davies and Lundberg 1985) support claims that timing of breeding is often energy limited in birds (Perrins 1970, Yom-Tov and Hilborn 1981). Early breeding is advantageous because 1 Present address: Department of Life Sciences, Indiana State University, Terre Haute, Indiana 47809 USA. it increases the probability of survival of fledged young (Campbell in Lack 1966; Nelson 1966; Perrins 1966, 1970, 1980; Nisbet and Drury 1972; Garnett 1981; Cooke et al. 1984; Newton and Marquiss 1984; Arcese and Smith 1985), raises the potential for rearing multiple broods or laying replacement clutches (Price 1984), and affects clutch size itself in species exhibiting a seasonal drop in clutch size. Examination of the relationship between body size and breeding date thus offers one means of testing for an energetic limit to the start of breeding. Eastern Kingbirds (Tyrannus tyrannus) annually raise a single brood of 3 or 4 young (Murphy 1983a). In all years clutch size declines seasonally, yet each season initial clutches of different females are laid as much as 5, but usually 4, weeks apart. Egg weight also exhibits wide variability. I have proposed that intrapopulation variation in kingbird egg weight reflects size differences among females and that kingbirds delay breeding to avoid weather-induced food shortages early in the breeding season (Murphy 1983a). Other observations, however, are consistent with the hypothesis that egg production is constrained by insufficient 465 The Auk 103: 465-476. July 1986 This content downloaded from 207.46.13.169 on Sat, 01 Oct 2016 06:24:13 UTC All use subject to http://about.jstor.org/terms 466 MICHAEL T. MURPHY [Auk, Vol. 103 resources. These include periods of up to 2 weeks between completion of nest construction and egg-laying, occasional suspension of laying during clutch production (Murphy 1983a), and a direct correlation between egg size and air temperature during the period of egg formation (Murphy 1985). In the present investigation I test the hypotheses that timing of breeding is energy limited in Eastern Kingbirds, and that egg size variation stems from size differences among females. I also examine the potential for an energy or nutrient limit to clutch size. Tests were made using information on body size and composition of female kingbirds with known reproductive histories, and through examination of egg composition and energy content.

Evolution of hole-nesting in birds: on balancing selection pressures

Abstract: RESUMEN.-Una re-examinaci6n de los dos especimenes conocidos de Philydor hylobius, ambos provenientes del Cerro de la Neblina en el sur de Venezuela, indic6 que estos pertenecen a Automolus roraimae. El tipo de P. hylobius correponde a un adulto de A. roraimae con predominancia de pigmentacion rojiza (eritrismo), y el otro especimen es un juvenil tipico. Por lo tanto, Philydor hylobius Wetmore and Phelps es un sin6nimo junior de Automolus roraimae Hellmayr.

Flight Cost of a Small Passerine Measured Using Doubly Labeled Water: Implications for Energetics Studies

Abstract: -The metabolic cost of rest and activity (cm3 CO2 g-1 h-') was measured for the European Robin (Erithacus rubecula, 18.6 g) at temperatures (Ta, C) from -15 to +30?C. Regressions expressing these costs are: night resting (MrN) = 4.23 0.0733Ta, day resting (MrD) = 5.10 0.0807T., hopping (MhOP) = 8.60 0.1256Ta. Daily energy expenditure (DEE) for robins held in an outdoor aviary was 64.8 kJ/day (SD = 9.2, n = 6), determined using the doubly labeled water technique. This was positively related to time spent in flight (tflY, h) such that DEE = 50.9 + 23.4ti,y. Flight cost for robins was estimated as 25.6 kJ/h (SD = 5.0, n = 6). This flight cost is about twice that predicted by various allometric equations. Robin flights in the aviary were short (3 m) and brief (0.78 s), indicating a mean flight speed (3.85 m/s) that was lower than the theoretical minimum power velocity (5.86 m/s). The European Robin has a relatively high wing loading (0.263 g/cm2) and aspect ratio (7.33). In a small bird with flapping flight these characteristics imply a high cost, particularly at low flight speeds. The high cost of flight was offset by its short duration. During 30-min observation periods, an average of 100.2 s was spent in flight, implying a sustained energy demand of only 3.04 kJ/h (2.7 x basal metabolic rate). The exceptionally high flight cost reported here (23 x basal metabolic rate) may be typical of short, brief aerial forays. Other doubly labeled water studies reveal a positive correlation between the time spent in flight and DEE, indicating its dominant impact on energy turnover in some free-living birds. Received 17 April 1985, accepted 19

Proximate and Ultimate Causation of Egg Size and the “Third-chick Disadvantage” in the Western Gull

Abstract: This is the publisher's version, also available electronically from http://www.jstor.org/stable/4087093?seq=1#page_scan_tab_contents.

Predation as a selective force on foraging herons effects of plumage color and flocking

Abstract: (Buteogallus anthracinus) and crocodiles (Crocodylus acutus) were observed preying on adult herons in Panama. Solitary herons were at greater risk than flocked foragers. White (immature) Little Blue Herons (Egretta caerulea) were attacked more frequently by hawks than were the blue adults of their species. Dark herons gave more alarms than white herons. Although flock size decreased in years of heavy predation and after attacks, mixed-flock composition remained the same. When flocks re-formed after hawk attacks, their members showed decreased foraging rates and increased interindividual distances. After repeated attacks, herons foraged in poorer habitats, under unfavorable climatic conditions, and under thermoregulatory stress. These results suggest that predation could be a potent force in maintaining color dimorphism in ardeids. Received 26 December 1984, accepted 7 January 1986.

Dynamics of nest parasitism in wood ducks

Abstract: Intraspecific brood parasitism is widespread among waterfowl (Weller 1959, Yom-Tov 1980, Andersson 1984). Often referred to as \"dump nesting,\" the phenomenon is particularly prevalent in Wood Ducks (Aix sponsa). In this species more than 50% of the nests may be parasitized, and clutches of 20-40 eggs, far exceeding a female's normal 11-15-egg capacity, are commonly observed (e.g. Grice and Rogers 1965, Morse and Wight 1969, Hansen 1971, Clawson et al. 1979). Although it is clear that supernormal clutches are produced by multiple females, the number of individuals contributing to each nest is unknown. We studied a population of Wood Ducks in southeast Missouri during the spring of 1985 to determine (1) the rate of egg deposition, (2) the minimum number of females laying in each clutch, and (3) behaviors associated with nest searching and laying. The study was conducted on a reservoir (\"Pool 1\") located in the Duck Creek Wildlife Management Area in Stoddard and Bollinger counties, Missouri. Pool ! was created in 1954 when a 718-ha tract of lowland

Brood parasitism in a host generalist, the shiny cowbird: i. the quality of different species as hosts

Abstract: ASSTRACT.--The Shiny Cowbird (Molothrus bonariensis) of South America, Panama, and the West Indies is an obligate brood parasite known to have used 176 species of birds as hosts. This study documents wide variability in the quality of real and potential hosts in terms of response to eggs, nestling diet, and nest survivorship. The eggs of the parasite are either spotted or immaculate in eastern Argentina and neighboring parts of Uruguay and Brazil. Most species accept both morphs of cowbird eggs, two reject both morphs, and one (Chalkbrowed Mockingbird, Mimus saturninus) rejects immaculate eggs but accepts spotted ones. No species, via its rejection behavior, protects the Shiny Cowbird from competition with a potential competitor, the sympatric Screaming Cowbird (M. rufoaxillaris). Cross-fostering experiments and natural-history observations indicate that nestling cowbirds require a diet composed of animal protein. Because most passerines provide their nestlings with such food, host selection is little restricted by diet. Species-specific nest survivorship, adjusted to appropriate values of Shiny Cowbird life-history variables, varied by over an order of magnitude. Shiny Cowbirds peck host eggs. This density-dependent source of mortality lowers the survivorship of nests of preferred hosts and creates natural selection for greater generalization. Host quality is sensitive to the natural-history attributes of each host species and to the behavior of cowbirds at nests. Received 4 June 1984, accepted 26 June 1985. VARIATION in resource quality can have great ecological and evolutionary consequences. Obligate brood parasites never build nests but leave the care of their eggs and young to other species, their hosts. The parental behavior of hosts is a critical and quantifiable resource to brood parasites. The first task in understanding the use of resources is to ascertain the quality of each alternative. I surveyed the quality of various passerine species as hosts of the Shiny Cowbird (Molothrus bonariensis) in Buenos Aires Province, Argentina. Host quality is tractable to analysis because selection is spatially and temporally focused at nests. Dimensions of host quality examined include response to parasitic eggs, nestling diet, and characteristic survivorship of each species' nests. This is the only systematic attempt to characterize the quality of an array of species for any brood parasite. The Shiny Cowbird is widely distributed throughout South America (Friedmann 1929). It is an extreme host generalist, known to have

Survival Analysis of Eggs and Chicks of AdÉlie Penguins (Pygoscelis adeliae)

Abstract: -Survival analysis was used to examine the fates of eggs in six colonies of Adelie Penguins (Pygoscelis adeliae) at Cape Bird, Antarctica. Hatching success was 56.2% and fledging success for chicks was 63.3%, giving an overall reproductive success of 35.6%. The major cause of losses of both eggs and chicks was predation by South Polar Skuas (Catharacta maccormicki). The second-most important causes of egg and chick mortality were desertion and starvation, respectively, both of which resulted from inadequate timing of nest relief. Eggs were at risk of predation by skuas throughout the incubation period, while chicks were at risk for the first 30 days after hatching. The likelihood of desertion increased after the eggs had been incubated for 16 days and reached a peak at 22-24 days. Starvation occurred during the guard stage and was most likely to occur when chicks were 6-8 days old. Timing of breeding and clutch size were factors that influenced the survival of eggs through the initial stage of incubation. Nest location had a significant effect on the survival of eggs and chicks, from laying through the end of the guard stage. Eggs laid in 2-egg clutches and in central nests were most likely to produce chicks that fledged. Received 17 April 1985, accepted

Songbird carcasses disappear rapidly from agricultural fields

Abstract: Evaluation de la disparition des carcasses d'oiseaux morts (par des predateurs detritivores) afin de permettre l'etude quantitative de l'effet des pesticides sur la mortalite des oiseaux en zone agricole

Report of the American Ornithologists' Union Committee for the Conservation of the Red-cockaded Woodpecker

Abstract: The American Ornithologists' Union's Committee for the Conservation of the Red-cockaded Woodpecker was formed in late 1983 by Dr. Thomas R. Howell, then president of the A.O.U., at the request of Warren B. King of the United States Section of the International Council for Bird Preservation. The Committee's charge was to review the status of the federally endangered Red-cockaded Woodpecker (Picoides borealis), to evaluate the conservation and management practices impinging on the welfare of this species, and to further the A.O.U.'s interest in providing scientific advice and suggestions to managers of threatened and endangered species of birds.

Male courtship vocalizations as cues for mate choice in the Satin Bowerbird (Ptilonorhynchus violaceus)

Abstract: -Male Satin Bowerbirds (Ptilonorhynchus violaceus) court females at specialized structures called bowers. Courtship includes a complex pattern of vocalizations in which a broad-band, mechanical-sounding song is followed by interspecific mimicry. We studied the effect of male courtship displays on male mating success in Satin Bowerbirds. Data from 2 years of field research showed low between-male differences in mechanical components of courtship song and high variability between males in mimetic singing. Older males sang longer and higher-quality bouts of mimicry than did younger males. In one year, courtship song features were correlated with male mating success. The results suggest that female Satin Bowerbirds use male courtship vocalizations in their mate-choice decisions. We discuss hypotheses about assessment of male age and dominance from courtship vocalizations and suggest that these songs have evolved as a result of selection for male display characteristics that provide females with information about the relative quality of prospective mates. Received 27 June 1985, accepted 20 September 1985. MALE Satin Bowerbirds (Ptilonorhynchus violaceus) build specialized structures called bowers that are used as sites for courting females and for mating (Vellenga 1970, Donaghey 1981, Borgia 1985). Females raise their young unassisted by males, and males do not associate with females after mating. Males decorate their bowers with a variety of natural objects and attempt to steal decorations and destroy the bowers of other males. Much effort has been focused on understanding the role of the bower and its decorations in female mating decisions. Borgia (1985) demonstrated a skewed distribution of matings among male Satin Bowerbirds, differences among males in bower decoration and construction, and a consistent pattern of female preference for males with well-constructed and well-decorated bowers. In addition, male mating success is influenced negatively by bower destruction and decoration-stealing (Borgia 1986a, Borgia and Gore 1986). Male courtship vocalizations are another component of male sexual display that may have important effects on female mating decisions. Male courtship is intense, involving dance movements and postures that are coordinated with the simultaneous production of complex vocalizations. The female crouches within the bower, closely observing the male during the display, and controls the outcome of the courtship either by signaling her willingness to copulate or by flying away. Given the complexity of male display and the attention females pay to displaying males, it is likely that male displays have an important effect on female mating decisions, yet there have been no detailed studies of display in any bowerbird

The influence of moonlight on the behavior of goatsuckers (Caprimulgidae)

Abstract: Etude de l'influence de la lune sur les activites de locomotion, sur les emissions sonores et la nidification de Caprimulgus vociferus

Relationships among territory size, habitat, song and nesting success of northern cardinals

Abstract: -We collected data from 30 territories of Northern Cardinals (Cardinalis cardinalis) during 3 breeding seasons (1979-1981) in eastern Texas. Territory size was positively correlated with tree height and negatively correlated with the density of foliage at ground level and at 3 m above the ground, and with the density of shrubs. Nesting success was positively correlated with presence of patchy understory foliage and arthropod biomass in territories. Cardinals with low song complexity and shorter songs held better-quality territories and had better nesting success than cardinals with more complex songs. We suspect that young males may use long, complex songs to establish a territory initially, and in subsequent years put less time and effort into song and more into care and defense of young. Received 15 January 1985, accepted 7 June 1985. THE functional significance of song in birds is a widely studied phenomenon. In particular, the significance of song repertoires has recently received extensive examination, resulting in many hypotheses. Krebs (1977a) summarized these hypotheses as follows: (1) repertoires enhance individual recognition (Emlen 1971, Brooks and Falls 1975); (2) repertoires are a product of sexual selection (Catchpole 1973, Kroodsma 1977); and (3) repertoires increase success in territorial competition by allowing acquisition of larger (Krebs 1977b) or betterquality (Howard 1974) territories. Large repertoires could permit matched countersinging among males establishing or defending territories (Lemon 1968, Verner 1975) or reduce habituation of listeners (Hartshorne 1956). Krebs (1977a) suggested a new mechanism (the Beau Geste hypothesis) whereby large song repertoires could be used to create the illusion that a particular habitat area was already saturated with numerous territorial males. Holding territory size constant, repertoire size of Northern Mockingbirds (Mimus polyglottos) in central and western Texas was correlated with measurements of territory quality (Howard 1974). Male mockingbirds with larger 3Present address: Math and Science Division, Bee County College, Beeville, Texas 78102 USA. repertoires also had the highest success in excluding other males and attracting females. If males with larger repertoires or some other song characteristic are able to establish and maintain larger or better-quality territories, such males should have a higher nesting success than males with territories of lesser quality. High-quality territories should have a greater availability of food and nest concealment than low-quality territories. Females from an inbred strain of canaries (Serinus canaria) exposed to playbacks of males with large repertoires built nests faster and laid larger clutches than did females exposed to small repertoires (Kroodsma 1976). Female birds may select males on the basis of song quality or select the territory of a male because of the habitat's appearance through mechanisms similar to those by which males may identify habitat quality. If either method was used, pairs in higher-quality habitat (more food and better concealment available) might be expected to produce more eggs or young on the average than pairs in lower-quality territories. Although predation would have a substantial impact on nesting success (Best 1978), vegetation structure or quality may also have an influence on predation and nesting success of birds (Best and Stauffer 1980). Vegetation characteristics around nests were correlated with nesting success of Vesper Sparrows (Pooecetes gramineus) in a 1-yr study in West Virginia 23 The Auk 103: 23-31. January 1986 This content downloaded from 207.46.13.131 on Sat, 15 Oct 2016 04:35:18 UTC All use subject to http://about.jstor.org/terms 24 CONNER, ANDERSON, AND DICKSON [Auk, Vol. 103 TABLE 1. Characteristics of cardinal songs and 100 randomly selected syllables from 30 territories over a 3-yr period in eastern Texas. Variable code Description Mean SD

Parental investment by the Northern Mockingbird: male and female roles in feeding nestlings

Abstract: --Analysis of 3,293 feeding trips to nestling Northern Mockingbirds (Mimus polyglottos) in the first 11 days of nestling life showed that males and females fed young at similar rates. Young were fed a mixed diet of animal prey and fruits, and males and females fed similar volumes of animal prey and of fruits. Females displayed a monotonic increase in feeding rate during nestling life but did not significantly increase load size. Males significantly increased both feeding rate and load size with age of nestlings, and their feeding rate peaked in the mid-nestling period, when young grow most rapidly. Males and females fed broods of two and three young at similar rates. There was a biased breeding-adult sex ratio in this population, with males outnumbering females. The unbalanced sex ratio may allow females to demand a high level of male parental care in feeding nestlings and in other behaviors included in parental investment. Received 19 April 1985, accepted 10 September 1985. PARENTAL investment (PI) is defined as "any investment by the parent in an individual offspring that increases the offspring's chances of surviving (and hence reproductive success) at the cost of the parent's ability to invest in other offspring" (Trivers 1972). When offspring are typically aggregated in clutches, some components of PI (e.g. nest defense) may be viewed as a compromise among clutches separated in time and space rather than among individual offspring (Wittenberger 1981: 362-363). Parental care (PC) is the nongametic subset of PI comprising those behaviors involved in raising young to independence. In many monogamous bird species, both males and females invest substantial amounts of time and energy in offspring, particularly in feeding nestlings and fledglings. In many monogamous passetines, males and females make roughly equal numbers of food deliveries to nestlings (Kendeigh 1952, Lack 1968, Emlen and Oring 1977, Oring 1982, Greenberg and Gradwohl 1983). However, the schedule of feeding nestlings and the amounts fed by the sexes seldom have been quantified rigorously. We studied parental feeding of altricial nestlings by Northern Mockingbirds (Mirnus polyglottos). Parental feeding of nestlings is a major time and energy investment in offspring (Ricklefs 1974, Skutch 1976, Breitwisch et al. 1984). Therefore, selection should favor male and female distribution of investment in feeding 152 nestlings in proportions that maximize genetic contributions to succeeding generations (Fisher 1958). We attempted to assess the relative contributions by males and females to feeding nestlings; to establish if the patterns of feeding by males and females were similar, both daily and throughout the nestling period; to find if the quality of food brought to nestlings by males and females was similar; and to see if there was a relationship between brood size and relative investment by males and females in feeding nestlings. In light of the limited theory related to these questions, we submit our empirical findings and interpretation as a partial basis for future development of theory regarding apportionment of parental investments by males and females. STUDY AREA AND METHODS This study was conducted on individually colorbanded Northern Mockingbirds inhabiting the main campus of the University of Miami, Dade Co., Florida (Merritt 1985). We observed parental provisioning of nestlings during 25 12-h periods (0600-1800) for a total of 300 h of observations. Data were gathered on 12 broods of 9 pairs of birds from 5 April to 9 July 1981 (23 of 25 periods between 1 May and 9 July). Four broods were observed for one day each, 4 broods for two days, 3 broods for three days, and 1 brood for four days. Broods sampled on two or more days were observed on nonconsecutive days, with one exception (see Breitwisch et al. 1984). We observed 1 brood when the young were six days old (= day 6), The Auk 103: 152-159. January 1986 January 1986] Mockingbird Parental Investment 153 3 broods at days 10 and 11, and 2 broods for each of the nine remaining days (days 1-5, 7-9, 12). Mockingbirds in southern Florida fledge at about 12 days of age. Brood sizes ranged from 1 to 4 (œ = 2.4, SD = 0.79, n = 12). Feeding trips to the nest were recorded to the nearest second with digital watches. Using binoculars, we identified food items to major type (e.g. fruit, insect, spider, lizard), with finer levels of resolution whenever possible (e.g. species of fruit or order of insect). We estimated lengths of animal prey ( 8 cm; size classes with lower limit closed and upper limit open). We estimated relative volumes of foods on an arithmetic scale of 1-5; volume per centimeter was estimated for animal prey. Volumes of all individual fruits were between 1 and 5, inclusive, although parents frequently brought more than one fruit in a single delivery. Volumes of all animal prey - 1 cm in length were calculated as (volume per centimeter) x (length in centimeters). Daily mean load sizes (• volume/trip) ranged from 2.51 to 6.85 for animal prey and 3.11 to 6.50 for fruit trips. We calculated total volume of animals and fruits fed per nest each day and divided these values by (12 x brood size) to yield mean food volume.nestling•. h-•. Unknown foods were distributed between fruit and animal categories based on the proportions of known items fed by each parent. We assigned to unknown foods the mean relative volumes of animals and fruits fed by each parental sex to nestlings at that age.

Comparative reproductive success of Yellow-shafted, Red-shafted, and hybrid flickers across a hybrid zone

Abstract: -Alternative hypotheses of hybrid zones make specific predictions about reproductive components of fitness in the hybrids. The dynamic-equilibrium and reinforcement hypotheses are premised on reduced hybrid fitness, which should be apparent as reduced clutch or brood size or as increased embryonic mortality. The hybrid-superiority and introgression hypotheses predict normal clutch and brood size and embryonic mortality. Reproductive success was measured at four study sites on a transect across the hybrid zone between the Yellow(Colaptes auratus auratus) and Red-shafted (C. a. cafer) subspecies of the Northern Flicker. Two additional clutch size samples representing pure Yellowand Redshafted flickers were obtained from museum egg collections. Mean clutch size did not differ significantly among the six samples. Factorial ANOVAs showed that early clutches and broods are larger than late clutches and broods, but no significant difference was detected between hybrid and parental study sites. Analyses of the effect of phenotype (yellow-shafted, red-shafted, hybrid) also suggest that neither clutch size nor brood size is affected, with the exception that hybrid males sired significantly smaller broods. Finally, there were no significant effects of type of cross (red-shafted male x hybrid female, etc.) on the ratio broodsize / clutch-size. The only evidence for reduced hybrid fitness was in the test where males with hybrid phenotypes appear to have sired small broods. This may indicate that abnormal behavior of hybrid males affects female fecundity, but it is also plausible that this marginally significant result is a type I statistical error. The overall lack of evidence for reduced hybrid fitness is inconsistent with either the dynamic-equilibrium or reinforcement models. Of the two remaining alternatives, the bounded hybrid-superiority model appears the more likely explanation of the Northern Flicker hybrid zone because earlier work (Moore and Buchanan 1985) showed that the hybrid zone is not becoming broader, as predicted by the introgression model. Received 20 February 1985, accepted 2 July 1985. HYBRID zones often occur between avian populations that have diverged to near the species level but retain contiguous distributions as a result of either secondary contact or parapatric divergence (Short 1969, Moore 1977, Rising 1983a). Typically, hybridization is rampant in the zone but the zone itself is very narrow and seems to act as a barrier separating markedly divergent plumage patterns or song types, or both. Furthermore, the biogeography of most avian hybrid zones suggests that they arose in antiquity, probably as a result of Pleistocene glaciation, and therefore seem to be evolutionarily stable configurations (Short 1970, Moore 1977; but see Barrowclough 1980). Three theories have been proposed to explain the existence of stable hybrid zones. Moore (1977) suggested that hybrid zones represent secondary contacts between taxa that had diverged in isolation but not to the extent that hybridization would disrupt distinctly coadapted gene complexes resulting in hybrid breakdown or hybrid unfitness. He further suggested that the secondary contact was established as distinct ecological communities expanded from refugia to form a "suture zone" in the sense of Remington (1968) and that the genes of the divergent characters are either adapted in their respective communities or closely linked to genes that are. The hybrid zone persists, then, because it occurs in an ecotone in which neither parental taxon is particularly well adapted. This was termed the hybrid-superiority model, although bounded hybrid superiority is more apt because it implies that hybrid superiority is restricted geographically. Barton (1979) and Barton and Hewitt (1981) 42 The Auk 103: 42-51. January 1986 This content downloaded from 157.55.39.28 on Thu, 15 Dec 2016 04:53:04 UTC All use subject to http://about.jstor.org/terms January 1986] Reproduction in Hybrid Flickers 43 developed an alternative hypothesis that explains stable hybrid zones by balancing opposing forces. The essential feature of the BartonHewitt dynamic-equilibrium model is hybrid unfitness, which prevents the hybrid zone from becoming broader through introgressive hybridization; less-fit hybrids form a narrower hybrid zone. Barton (1979) showed that hybrid unfitness itself can fix the width of the hybrid zone and further showed that variations in population density could prevent the hybrid zone from "flowing" geographically. The third alternative is that the hybrid zone appears stable only to a short-lived observer but actually is growing broader through introgressive hybridization or becoming more restricted as premating reproductive isolation is reinforced by selection against hybrids (Wilson 1965, Remington 1968). Whether introgression or reinforcement is expected would depend on whether hybrid phenotypes are at least as fit as the parental phenotypes or less fit, respectively. The three alternatives provide radically different explanations of hybrid zones, each with its own implications for speciation theory. Furthermore, the alternatives appear to be testable, as the dynamic-equilibrium and reinforcement models predict some measure of hybrid breakdown, whereas the hybrid-superiority and introgression models do not. More precisely, according to the dynamic-equilibrium and reinforcement models, one would expect increases in infertility and development aberrations in hybrid phenotypes. The pairs of alternatives can be tested further by studying the historical stability of the hybrid zone. The idea that hybridization between distinctly coadapted gene pools results in hybrid breakdown is an old idea in evolutionary biology that is of particular importance to speciation theory. Collectively, the assorted maladies that are expected to result are termed postmating reproductive isolating mechanisms. Although hybrid breakdown could manifest at any stage in the life cycle, the maladies most often mentioned affect the early development or fertility of hybrid phenotypes. Thus, where natural hybridization has disrupted coadapted gene complexes, one would expect higher frequencies of developmental anomalies and reduced fertility. In birds this should appear as reduced brood and clutch sizes, respectively. We report clutchand brood-size data for four populations of the Northern Flicker (Colaptes auratus) along a transect across the hybrid zone between the Yellowand Red-shafted flickers (C. a. auratus and C. a. cafer) in western Nebraska and eastern Wyoming. The two central locales support hybrid populations, whereas the distal locales represent parental populations (see Fig. 1). Our purpose is to determine whether hybridization between these wellmarked subspecies has disrupted coadapted gene complexes and whether hybrid breakdown is essential to understanding this hybrid zone. Data pertaining to historical stability were reported earlier (Moore and Buchanan 1985). The structure of the hybrid zone has been reported by Short (1965) and Moore and Buchanan (1985). To summarize briefly, the Yellow-shafted Flicker is broadly distributed in diverse woodland types across eastern North America, whereas the Red-shafted Flicker is the western North American counterpart. The hybrid zone occurs on the western Great Plains, primarily in riparian woodlands (cottonwood, peach-leaved willow, and green ash) but also in the coniferous forests of the Black Hills, the Pine Ridge region of Nebraska and South Dakota, and in the Cypress Hills of Saskatchewan. The hybrid zone may be continuous in the solidly forested montane regions of Alberta, British Columbia, and southern Alaska (Short 1965, Moore pers. obs.). The two subspecies exhibit contrasting conditions for 6 (5 in females) plumage characters; e.g. red-shafted males have a red malar stripe, whereas that of the yellowshafted is black. Hybrids exhibit intermediate variations. These characters are easily scored, even with binoculars. Mating is random with regard to the plumage characters (Short 1965, Bock 1971, Moore and Buchanan 1985). The hybrid zone varies in width and is asymmetrical, with introgression evident farther west of center than east (see Fig. 1). Population densities are uniformly high along the study transect (Moore and Buchanan 1985). MATERIALS AND METHODS Active nests were located throughout May and June in 1981-1984 at four study sites on a transect across the hybrid zone (Fig. 1). The study sites are: Sutherland (James Haugland farm on the south bank of the South Platte River between the river and interstate highway I-80, 1.75 km south-southeast of Southerland, Lincoln Co., Nebraska, R33W, T14N, secs. 32, 33); Bridgeport (Blanchard-Lindgren ranch on the This content downloaded from 157.55.39.28 on Thu, 15 Dec 2016 04:53:04 UTC All use subject to http://about.jstor.org/terms 44 MOORE AND KOENIG [Auk, Vol. 103 CONTOUR MAP OF FLICKER HYBRID ZONE

The Social System of the Texas Green Jay

Abstract: -Accessory birds were absent at the nests of Green Jays (Cyanocorax yncas). However, young stayed in the family flock for one year. After the young from the following year fledged, the 1-yr-old young were forced from their natal territory by the breeding male. These young either dispersed into adjacent habitat or became floaters within their former territories until, possibly, a breeding position opened up in a family flock. The yearlings provided a significant amount of territorial defense, which freed the breeders of much of the energetic costs inflicted on them by the stringent territoriality required in south Texas