Showing papers in "The Auk in 1992"

Proximate basis of variation in carotenoid pigmentation in male house finches

Abstract: In the wild, male House Finches (Carpodacus mexicanus) vary in plumage color from pale yellow to bright red. I investigated the proximate basis of this variation in plumage brightness, as well as the basis for variation in the extent of ventral carotenoid pigmentation. Regardless of their age or coloration in the wild, captive males converged on a similar appearance after completing prebasic molt on a standardized diet, with significantly less variance in coloration than is found among wild males. Captive males that were fed a diet deficient in carotenoid pigments grew pale yellow feathers; males fed a diet supplemented with -carotene grew pale orange feathers; and males fed a diet supplemented with can- thaxanthin grew bright red feathers. Stored carotenoids did not appear to be an important source of feather pigments. Red males captured from the wild just prior to fall molt and fed a carotenoid-deficient diet did not grow more colorful feathers than males that had been held in captivity on a carotenoid-deficient diet for six to nine months prior to fall molt. In a wild House Finch population in southeastern Michigan, the mean plumage coloration of yearling males was significantly drabber than the mean coloration of older males, although both groups displayed approximately the same range of coloration. Wild males tended to become brighter between their first and second springs, but thereafter, males tended to display a similar plumage coloration between years. The extent of ventral carotenoid pigmentation (color-patch size) also was partly dependent on carotenoid intake. Captive males whose diet was supplemented with canthaxanthin produced significantly larger patches after captive molt than before captive molt, and canthaxanthin-supplemented males also expressed sig- nificantly larger patches than males in the carotenoid-deficient or -carotene-supplemented groups. Among wild males, there was a significant positive correlation between patch size and plumage brightness. Received 17 September 1990, accepted 24 July 1991.

Is density an indicator of breeding success

Abstract: -A new method of measuring reproductive success was used to test Van Horne's (1983) contention that reliance on population density as a measure of habitat quality can produce misleading results. None of the three emberizine sparrows in this study showed a clear correlation between high territory density and high reproductive success. Grasshopper Sparrows (Ammodramus savannarum) were most successful in medium-density plots, and did poorly when territory density was low. Savannah Sparrows (Passerculus sandwichensis) were significantly more successful at low density, and were least successful at high density. Vesper Sparrows (Pooecetes gramineus) were the only species whose reproductive success was unaffected by territory density and, thus, for which density would have been a reasonable measure of habitat quality. These results lend support to Van Horne's thesis that the singular use of density may be a poor indicator of habitat quality and that additional factors should be considered. Received 5 March 1991, accepted 10 February 1992. POPULATION DENSITY frequently is used as an indicator of a habitat's quality, because a greater number of individuals within a given area is generally thought to reflect larger amounts of the necessary resources to sustain a species (Van Horne 1983). By extension, it often is assumed that concentration of resources allowing a high population density also will be reflected in greater reproductive success, or other indices of fitness. Because density is easier to measure than fitness, Flood et al. (1977) and others who model habitat relationships have used density to make inferences about habitat quality, although not necessarily with a high degree of predictive success (Lancia et al. 1982, Bart et al. 1984, Maurer 1986). Van Horne (1983) questioned the singular reliance on density as an indicator of habitat quality and suggested that inferences about which habitats support individuals with the highest fitness often may be false. She suggested that, from a populationviability and management perspective, it is preferable to define habitat quality as a product of density and reproductive success. To test the hypothesis that density is a reasonable index of nesting habitat quality for three grassland sparrows, we examined the relationship between 3Present address: Conservation Department, Massachusetts Audubon Society, Lincoln, Massachusetts 01773, USA. 4Present address: Department of Natural Resources, Field of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York 14853, USA. breeding densities and reproductive success for each species. METHODS The study site was located on a sandplain grassland in Kennebunk, York County, Maine (43024'N, 70?59'W). We studied three emberizine sparrows: Vesper Sparrow (Pooecetes gramineus); Savannah Sparrow (Passerculus sandwichensis); Grasshopper Sparrow (Ammodramus savannarum). Vickery et al. (1992) provided additional information on site and methods. The site was managed for commercial blueberry production with one-half of the area mowed and burned on a biennial rotation. This management created profound year-to-year changes in the vegetation structure with a concomitant influence on habitat quality. These habitat manipulations allowed us to measure the avian response to these year-to-year changes in each plot. To examine the relationship between territory density and reproductive success, territories were "spot mapped" (International Bird Census Committee 1970) using eight replicate censuses on eight plots (8-24 ha) for three years (1984-1986). For each species, plots were assigned to a class depending on territory density: low, '2.5 territories per 10 ha; medium, >2.5 to <3.5 territories per 10 ha; high, 23.5 territories per 10 ha. There were at least four plots for each density category. The reproductive-index rank (Vickery et al. 1992) for each territory was assigned to the appropriate density category. We then used the KruskalWallis test (Conover 1980:229) to determine if there were differences in the reproductive-index rankings within each density classification. We measured percent cover for nine vegetation features for high-success and low-success Grasshopper, Savannah and Vesper sparrows, and also measured the same parameters on the unoccupied habitat in each plot. To evaluate whether Savannah Sparrows

Mitochondrial DNA Phylogeographic Differentiation among Avian Populations and the Evolutionary Significance of Subspecies

Abstract: ABsTRAcr.-Phylogeographic population structures revealed by restriction analyses of mitochondrial (mt) DNA were assessed within each of six avian species with continentwide distributions in North America. The magnitude and geographic pattern of mtDNA variation differed considerably among species. The Downy Woodpecker (Picoides pubescens) and Mourning Dove (Zenaida macroura) exhibited little mtDNA polymorphism and a shallow phylogeographic structure. The Brown-headed Cowbird (Molothrus ater) and Song Sparrow (Melospiza melodia) showed somewhat higher nucleotide diversity, but no evidence of long-standing population separations. For each of these four species, evolutionary effective sizes of female populations estimated from mtDNA were substantially smaller than population sizes at the present time, suggesting historical demographic constraints on the numbers of females through which mtDNA lineages successfully have been transmitted. In contrast, the Rufous-sided Towhee (Pipilo erythrophthalmus) and Common Yellowthroat (Geothlypis trichas) showed relatively deep mtDNA separations (mean nucleotide sequence divergence p = 0.008 and p = 0.012, respectively) between populations in Washington versus those in the central and eastern states. In the case of the Rufous-sided Towhee, the mtDNA clades may correspond to morphological and behavioral differences distinguishing the western "Spotted Towhee," which was formerly recognized as a distinct species. Overall, however, most of the taxonomic subspecies currently recognized within the six assayed species were genetically very close, and showed no obvious mtDNA differences. These results raise questions concerning the population-genetic and evolutionary significance of current subspecies designations in ornithology. Received 5 June 1991, accepted 23 February 1992.

Polymerase-Chain-Reaction (PCR) Analysis of Microsatellites: A New Approach to Studies of Genetic Relationships in Birds

Abstract: ABSTRAcr.-Genomic DNA libraries of the Barn Swallow (Hirundo rustica) and the Pied Flycatcher (Ficedula hypoleuca) were screened for the presence of dinucleotide microsatellite repeats. Two thymine-guanine repeats, "(TG),," and two thymine-cytosine repeats, "(TC)n," were isolated and sequenced from the two species, respectively. Polymerase-chain-reaction (PCR) analysis of 25 unrelated Barn Swallows and 10 unrelated Pied Flycatchers revealed 3 to 15 alleles per locus and heterozygosities in the range of 0.46 to 0.89. Mendelian inheritance was confirmed for all four loci in 10 Pied Flycatcher and 2 Barn Swallow families comprising a total of 240 meioses. The occurrence of nonparental alleles in offspring from two Barn Swallow families was consistent with extrapair fertilization as revealed by a parallel DNAfingerprinting analysis. A DNA amount approximately corresponding to 0.01 ;Il blood was used for PCR analysis. DNA was also prepared from feathers and approximately 1% of a preparation from a single remex or rectrix was sufficient for PCR amplification. One of the primer pairs from the Barn Swallow also amplified a polymorphic locus in the House Martin (Delichon urbica) and in the Bank Swallow (R. riparia). Received 3 October 1991, accepted 16 June 1992.

Test of the Ecological Basis of Cooperative Breeding in Red-Cockaded Woodpeckers

Abstract: -In many cooperatively breeding birds, the primary reason that helpers remain on the natal territory rather than disperse to breed independently may be to gain an advantage in competing for high-quality habitat. We hypothesized that cavities excavated in living pines, because they require much time to construct, are the critical determinant of habitat quality that has led to cooperative breeding in Red-cockaded Woodpeckers (Picoides borealis). These woodpeckers rarely colonize sites that lack existing cavities. To test our hypothesis we drilled cavities in 20 unoccupied sites. Eighteen were occupied subsequently, but none of 20 control sites were used. The manipulation added 12 new social units (breeding pairs or unpaired territorial males) to the population. New groups mostly comprised previous helpers and dispersing first-year birds. These results support our contention that variation in habitat quality dependent on the presence or absence of cavities is the ecological basis of group formation in Red-cockaded Woodpeckers. Cavity construction may be used to increase the number of groups in a population, and to prevent territory abandonment when bird-constructed cavities are lost. Received 3 October 1990, accepted 24 June 1991. COOPERATIVE breeding refers to a social system found in birds and mammals in which some reproductively mature individuals (helpers) assist others in raising young (Brown 1978, 1987, Emlen and Vehrencamp 1983, Emlen 1992). Understanding the evolution of cooperative breeding involves two interrelated but distinct issues (Emlen 1982a, b, 1992, Brown 1985, 1987, Ligon and Stacey 1989): (1) determining what leads individuals to remain with their natal groups or form groups rather than disperse to breed independently; and (2) determining why such individuals engage in helping behavior such as feeding young. Altruism evolved through kin selection is an accepted explanation of helping behavior (issue 2; Emlen and Wrege 1988,1989). In contrast, remaining in the natal group (issue 1) and thereby delaying reproduction and altering dispersal behavior generally is viewed as producing direct benefits to the individual under certain conditions (Emlen 1982a, Woolfenden and Fitzpatrick 1984, Brown 1985, 1987, Stacey and Ligon 1987). Emlen (1982a) outlined two conditions under which remaining with the natal group may result in greater lifetime reproductive success than early dispersal and breeding. One condition involves a harsh, unpredictable environment. In I Present address: RD1, Box 27, Spring Mills, Pennsylvania 16875, USA. poor years, inexperienced birds reproduce poorly, so that living with the natal group is favored over independent reproduction. This hypothesis may apply to species that inhabit the dry regions of Africa and Australia (Reyer 1980, Emlen 1981, 1982a, Clarke 1984). The second, perhaps more common condition has traditionally been termed habitat saturation, because it is thought to result from a shortage of vacancies in breeding habitat (Selander 1964, Brown 1969, Stacey 1979, Emlen 1982a). An apparent lack of unoccupied territories has been noted in many cooperative breeders (e.g. Selander 1964, Ridpath 1972, Woolfenden 1975, Ligon and Ligon 1978, Walters and Walters 1980, Zack and Ligon 1985, Koford et al. 1986), but not all (Rabenold 1985). In species to which the habitat-saturation hypothesis has been applied, helpers remain on their natal territory and compete for breeding vacancies on and in the immediate vicinity of the natal territory (stay-andforay, abbreviated SAF), rather than dispersing after fledging to wander in search of a breeding vacancy (depart-and-search, DAS; Brown 1987). Those practicing SAF appear to have an advantage in competing for positions in their vicinity over those practicing DAS (Zack and Rabenold 1989), perhaps because they can monitor the availability of those positions much more effectively. The demographic conditions under which SAF may be selected over DAS have been mod-

Use of a New Reproductive Index to Evaluate Relationship Between Habitat Quality and Breeding Success

Abstract: -A new method of measuring reproductive success is proposed that uses a composite of breeding-behavior observations (for behaviors that reflect different stages in the reproductive cycle) as an index of fitness. This reproductive index does not rely on discovery of nests, but is comprehensive in that it includes information on all monitored territories. The reproductive index was applied to three co-occurring grassland emberizine sparrows, two of which required special care because of their regional rarity. Ranks derived from this reproductive index were used to distinguish territories of birds of known high success (i.e. those that fledged young in at least one brood) from territories of birds with known low success (unpaired males), and were compared with findings for "spot-mapped" territories. Principal-components analyses of habitat measurements for these territory types revealed a similar pattern for all three species: spot-mapped territories overlapped broadly with nonterritory (unoccupied) plots, whereas high-success territories formed a discrete, isolated cluster within the spot-map matrix. Univariate analyses revealed that high-success territories were described by 15 vegetation features that differed (P < 0.01) from nonterritory values, whereas in spot-mapped territories only 8 vegetation measures differed and in lowsuccess territories only 2 differed. The ability to distinguish high-success territories allowed us to identify a greater number of habitat features that were correlated with reproductive success. If we had relied on the spot-mapping method, we would have been unable to identify many of these important habitat features. Yet, the ability to make such discriminations is likely to be critical in the management of threatened species. Received 5 March 1991, accepted 7 April 1992. THE DIFFICULTY of being able to gather detailed reproductive information about a bird 3Present address: Conservation Department, Massachusetts Audubon Society, Lincoln, Massachusetts 01773, USA. 4 Present address: Department of Natural Resources, Field of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York 14853, USA. population or community in a time-efficient manner has frequently limited avian-community research (e.g. Wiens 1973). Techniques for quantifying avian reproductive activity usually fall into two general categories. The simplest method, territory mapping, allows the researcher to define the location of individual male territories for a species or group of co-occurring species (Kendeigh 1944, International Bird Cen-

Multiple brooding and productivity of a neotropical migrant, the black-throated blue warbler (dendroica caerulescens), in an unfragmented temperate forest

Abstract: We studied a population of Black-throated Blue Warblers (Dendroica caerules- cens) in the White Mountains of central New Hampshire to determine the reproductive performance of this Neotropical migrant species in an unfragmented north-temperate forest. Over a four-year period (1986-1989), female Black-throated Blue Warblers laid an average of 6.6 eggs per season of which 5.2 hatched and 4.3 fledged. This high annual production of young was due to a combination of overall high nesting success (63%), low nest depredation rates (22%), no brood parasitism, and, most importantly, frequent multiple brooding (48%). Over the four years, 35% (range = 14-50%) of the individually-marked females in this pop- ulation successfully fledged two or more broods; one female fledged three successive broods in one season. Multiple brooding accounted for most of the annual variation in numbers of young fledged per female, and its frequency was related to annual differences in food abun- dance and, potentially, to time constraints imposed by the intensity and timing of nest depredation. Multiple brooding was significantly and positively related to age of the male parent, and possibly the female parent. Older males were also more likely to be polygynous, although such matings were infrequent (4-16% of mated males each year). Higher repro- ductive output by older individuals implies that demographic structure of Neotropical mi- grant populations may have important consequences for maintenance of population size. Recruitment of yearling male Black-throated Blue Warblers into the population was positively related to the number of young fledged per female in the preceeding summer. Although not statistically significant, this finding in combination with the above results and other published information suggests that reproductive success and the factors affecting it may be particularly important in influencing the abundance and population dynamics of this Neotropical migrant passerine, and may overide the impact of events occurring in winter or on migration. Received 6 May 1991, accepted 2 December 1991. RECENT evidence suggests that many North American bird populations are declining, es- pecially those that breed in temperate forests and winter in the Neotropics (Robbins et al.

Daily Mass Gains Among Woodland Migrants at an Inland Stopover Site

Abstract: We investigated fat deposition in transient, nocturnal, long-distance migrants at a wooded stopover site that is not near an ecological barrier (e.g. desert, large water body). The changes in body mass of recaptured birds have traditionally been used as a measure of mass gains at stopover sites. This technique ignores the majority of transients, however, possibly hindering the ability to answer species-level questions regarding stopover mass gain. We compare an analysis of recaptures with a technique that considers all captures and their condition by time of day. Eleven woodland-associated migrant species were analyzed, as well as a resident species (Black-capped Chickadee, Parus atricapillus) for comparison. Based on recapture data alone, our study site appears to be primarily a location of mass loss, rather than one of fat deposition. Conversely, the examination of condition by time of day suggests that individuals of several species have net daily gains greatly exceeding those of recaptured individuals. During autumn, however, several species exhibited net daily losses. Although some of these losses may be related to molt, it seems unlikely that molt is the only contributing factor. Differences among species in mass gains at our site suggest that various fat-deposition patterns (and, thus, migration strategies) may occur among migrants that are not approaching ecological barriers. Received 10 December 1991, accepted 11 March 1992.

Short-Term Effects of Hurricane Gilbert on Terrestrial Bird Populations on Jamaica

Abstract: Four months after Hurricane Gilbert we resampled 10 habitats that were sam- pled previously in December 1987 Overall, we found no change in the total number of species nor in the mean number of individual birds detected The mean number of individuals declined in three montane habitats (cloud forest, pine plantation, and coffee plantation), where structural damage to tree trunks and branches was often severe, and trees were still defoliated In the mountains, higher proportions of nectarivores and fruit ! seedeaters declined than insectivores We found increased mean numbers of individuals in two lowland sites (wet limestone forest and mangroves), where structural damage to trees was also severe, but where new foliage was present Mean numbers of individuals did not change in five other lowland habitats, despite varying levels of vegetation damage Populations of several species declined in some habitats and increased in others, a pattern consistent with interhabitat migration Population declines in montane habitats were related to diet, suggesting that Hurricane Gilbert's greatest stress on Jamaica's montane bird populations occurred after its passage rather than during its impact Frequent hurricanes may contribute to some of the commonly observed characteristics of the Caribbean avifauna Received 5 March 1991, accepted 10 July 1991 IN SOME tropical regions, hurricanes occur with sufficient frequency to be important fac- tors in determining the structure and species composition of biotic communities (eg Wads- worth and Englerth 1959, Odum 1970) For bird populations in particular, hurricanes can have both direct and indirect effects (for recent re- view, see J Wiley, unpubl manuscript) Direct hurricane effects include death from exposure to high winds and rain (Kennedy 1970) Indi- rect effects of hurricanes on bird populations include destruction of food supplies (or nesting, roosting, and foraging substrates) by the storm's high winds (Jeggo and Taynton 1980) Further- more, storm-weakened birds may be at greater risk to predation, particularly in the absence of vegetative cover or roosting sites for protection (Engstrom and Evans 1990) Hurricanes can dis- rupt normal migration patterns and, in some instances, change the geographic distributions of species (Thurber 1980) Following hurri- canes, humans may kill weakened birds and accelerate the rate of habitat destruction

Ontogenesis of Intestinal Nutrient Transport in Domestic Chickens (Gallus gallus) and Its Relation to Growth

Abstract: ABSTRACr.-We measured intestinal (brush-border) uptake of the sugars glucose and fructose, and of the amino acid proline, each week from one day posthatching to 12 weeks of age in a rapidly growing strain of domestic chicken (Gallus gallus, White Cornish x Rock). Small-intestine mass increased as the 0.74 power of body mass, the same power as resting metabolic rate of the whole bird. Even on a constant diet, nutrient uptake varied with age, according to ontogenetic patterns that differed among nutrients. From the beginning to end of the 12-week period, glucose uptake per milligram of intestinal tissue remained on the average approximately constant, fructose uptake increased in the distal intestine, and proline uptake per milligram declined across all intestinal regions. Uptake capacity integrated over the whole length of the intestine generally increased for all three solutes, mostly as a consequence of increases in intestinal mass. A steep, brief, many-fold increase in glucose uptake appeared in two-week-old chicks, coinciding with increasing thermal independence and the exhaustion of yolk reserves. A similarly steep, brief, many-fold increase in proline uptake at week 6 coincided with the onset of molt and high relative growth rates. Comparisons of integrated nutrient-uptake capacities with estimated nutrient intakes suggest that intestinal nutrient uptake capacity is closely matched to dietary nutrient intake during growth. This supports the hypothesis that the intestine's capacity to assimilate nutrients may pose a proximal constraint on the rate of growth in precocial species. Received 1 November 1990, accepted 6 February 1992.

Water and Energy Limitations on Flight Duration in Small Migrating Birds

Abstract: -We examined the physiological limitations to flight duration in small migrating birds with a computer-simulation model. Given preflight body mass, fat and water contents, and flight-path meteorological data, we calculated water and energy budgets and possible flight time. The model can be applied to birds of any size that migrate by flapping flight. As an example, we simulated the flight of small Palearctic passerines (body mass = 10 g) during their annual migration over the Sahara desert. Sensitivity analysis of model input variables indicated that oxygen extraction and expired air temperature are the most important physiological variables in a bird's water budget and can profoundly influence flight duration. This manifests the importance of: (1) efficient cooling in the nasal passages of flying birds; and (2) the choice of flight altitude (which affects both ambient air temperature and expired air temperature). The model predicted that: (1) Prior to migration, these birds must have stored fat comprising at least 22% of their initial body mass; otherwise, they cannot complete their journey. (2) In relatively fat birds (stored fat > 0.22 body mass), dehydration rather than energy will limit flight duration. (3) Birds should fly at an altitude not exceeding 1,000 m to cross the Sahara successfully. (4) Even in low-flying fat birds, flight duration will be limited by their stringent water budget. The model further predicted that small passerines cannot cross the Sahara in a 30to 40-h nonstop flight, as commonly accepted, but should confine flying to the cooler hours (i.e. nights) and rest during the day in order to avoid elevated rates of water loss due to higher ambient air temperatures. Available data and observations of birds trapped at stopover sites in the Sahara support these predictions. Received 26 February 1991, accepted 13 January 1992. LONG-DISTANCE flight over seas or deserts is perhaps the most risky and physiologically challenging event in the life cycle of migratory birds (Moreau 1961, Wilson 1981). Reports of high attrition among migrants and of exhausted birds found severely dehydrated and/or fat depleted (Serle 1956, Odum et al. 1964, Rogers and Odum 1964, Johnston 1968, Wilson 1981) raised the question: Is water or energy the greater physiological limitation to bird flight duration? Energy, rather than water, is currently considered the major factor limiting bird flight duration because dehydration can be avoided by flying at high altitudes where air temperatures are low (Blem 1976, Torre-Bueno 1978, Skadhauge 1981, Dawson 1982, Biesel and Nachtigall 1987, Biebach 1990). However, this paradigm has not been substatiated with empirical field

Establishing paternity in whooping cranes (Grus americana) by DNA analysis

Abstract: -DNA fingerprinting was used to study paternity and genetic variability within a captive flock of Whooping Cranes (Grus americana). Fingerprint patterns for 42 individuals were obtained by digesting genomic crane DNAs with HaeIII followed by electrophoresis, blotting, and hybridization to the M13 minisatellite probe. Despite finding reduced levels of genetic variation in the Whooping Crane due to a population "bottleneck," these polymorphisms were successfully used to determine paternity in six of seven cases of captive propagation where the maternal-offspring relationship was known, but where the sire was unknown. These determinations of paternity are required for effective genetic management of the crane flock. These results also revealed a number of heterozygous minisatellite loci that will be valuable in future assessments of genetic variability in this endangered species. Received 10 July 1991, accepted 10 February 1992. THE WHOOPING CRANE (Grus americana) is a highly endangered species. Today's 221 surviving individuals are all descendants of a single natural population that nests in Wood Buffalo National Park, Canada, and over-winters at Aransas National Wildlife Refuge near Austwell, Texas. The wild Wood Buffalo population reached a low of 15 birds in 1941 and then slowly increased to 48 in 1967, and to 142 in 1990 (Erickson 1968, Ellis et al. 1991). Besides the 142 cranes making up the Wood BuffaloAransas population, in 1990 there were 66 individuals in captivity and 13 in an experimental transplant-release program in Idaho. Due to its endangered status, the Whooping Crane has been the subject of intense efforts aimed at preservation and recovery of the species. These efforts have included ecological study, habitat management, and reintroduction (U.S. Fish and Wildlife Service 1986, Canadian Wildlife Service 1988). A captive propagation program was initiated at the Patuxent Wildlife Research Center in Laurel, Maryland, in 1965. Relying principally on artificial insemination, this project has produced 50 captive-reared cranes since 1975, and has supplied 73 fertile eggs for transplant release. Whooping Cranes represent a substantial captive investment due to slow sexual maturity and low reproductive capacity (only 60% of eight-year-old captive females have produced eggs, and only five or six eggs are produced per female per year). In order to maximize the production of fertile eggs, adult females often were inseminated with semen from several males. In these cases, the female parent was known, but the sire was not known. The unknown paternities pose a significant impediment to future breedings. In order to avoid the possibility of inbreeding, female offspring could not be mated with any of their possible sires. In addition, it was not possible to distinguish sibling and half-sibling relationships among these offspring. Determining paternal relationships, thus, would benefit those involved in the genetic management of the captive Whooping Crane flock. Although knowledge of paternity has been needed for some time, conventional techniques (such as allozyme analysis) have failed to resolve paternity in most birds, including these cranes. However, the recent development of DNA fingerprinting (or DNA profiling) has made it feasible to perform meaningful paternity testing in avian species. This technique makes use of "minisatellites," which are short tandemly repeated DNA sequences. An interesting feature of minisatellites is that the nu-

Avian forelimb muscles and nonsteady flight: can birds fly without using the muscles in their wings?

Abstract: AlsTRACT.--Intensity patterns of electromyographic (EMG) signals from selected muscles of the wing were studied during different modes of flight in trained Rock doves (Columba livia). Shoulder muscles exhibited a stereotypic pattern producing maximal EMG intensity during the deceleration phases of the upstroke and the downstroke, whereas the muscles of the brachium and antebrachium acted primarily as joint stabilizers during level flapping flight. During nonsteady flight (e.g. takeoff, landing, vertical ascending flight), the distal forelimb muscles exhibited maximal EMG intensity; their primary function appears to be associated with changing the camber and planform of the wing during rapid oscillation. During steady flight, an automatic linkage system consisting of forelimb skeletal elements and ligamentous attachments is thought to permit proper excursion of the wing as a result of forces generated solely by proximal muscles of the wing. To test this hypothesis, the medianoulnaris and radialis nerves were cut in five animals, thus eliminating the contribution of the forearm muscles, and flight tests were performed. Even though forearm muscles were incapable of contracting, the birds were capable of sustained level flapping flight. They were unable to take off independently or perform controlled landings. Received 3 October 1991, accepted 29 March 1992. DESPITE THE large number of bird species, the wide range of wing shapes (Savile 1957), and variation in flight styles or wing-beat gaits (Ray- net 1988), natural selection has acted to retain the basic musculoskeletal design of the avian forelimb. Few data exist on the functional re- lationship between a species' flying capabilities and its forelimb musculoskeletal architecture. Previous studies of the musculoskeletal system document structural variation, but few studies (see Brown 1948, Fisher 1946, Sy 1936) address the functional aspects of forelimb components. Compared with terrestrial locomotion, flying is metabolically efficient per unit distance trav- elled, but energetically expensive per unit time (Tucker 1968, Schmidt-Nielsen 1984); this is due to the muscular demands associated with gen- erating lift using a rapidly oscillating append- age. Consequently, the musculoskeletal appa- ratus of the avian forelimb should be subject to considerable selective pressures. One way to minimize the moment of inertia of a rapidly moving appendage is to distribute the mass closer to the pivot (Hildebrand 1988). This phe- nomenon is evident among birds as the bulk of the wing's mass is positioned proximally. In

Effects of parental age on hatching asynchrony, egg size and third-chick disadvantage in western gulls

Abstract: We examined the relationships among parental age, hatching asynchrony, egg size, and the "third-chick disadvantage" of Western Gulls (Larus occidentalis) on Southeast Farallon Island, California, during the 1984-1990 breeding seasons. Third chicks showed lower survival than first or second chicks for all parental age classes combined. Fledging success of first- and second-hatched chicks was related to parental age in a parabolic fashion, whereas fledging success of the third chick increased sigmoidally with increasing age; the probability of fledging of first-, second-, and third-hatched chicks converged for birds greater than 15 years old, negating the third-chick disadvantage for the oldest parents. Egg volume increased with increasing age for females 4 to 13 years old, and levelled off or declined slightly thereafter. For older females, the size disadvantage of third-laid eggs was relatively less than for younger females. Egg volume did not affect fledging success when parental age and year were considered in a multiple logistic (binomial) regression analysis. Hatching asynchrony decreased slightly with increasing parental age. Fledging success of third-hatched chicks decreased significantly with increasing hatching asynchrony. The greater hatching synchrony in broods of older parents may increase the competitive ability of third chicks. The third-chick disadvantage, often viewed as an adaptive response to variable food supplies, may be a nonadaptive effect of resource availability governed, in part, by the foraging

Physiology of Prolonged Fasting in Greater Snow Geese (Chen caerulescens atlantica)

Abstract: -Greater Snow Geese (Chen caerulescens atlantica) may face periods of complete food deprivation during incubation in the High Arctic. We studied the ability of these birds to withstand a prolonged fast. We measured rate of mass loss, patterns of carbohydrate, lipid and protein utilization, and changes in resting metabolic rate in 11 captive geese subjected to complete food deprivation. Geese lost 44% of their initial body mass during fasting periods that ranged from 19 to 42 days (mean 34 days). The rate of mass loss reflected the three phases commonly associated with the changing rates of lipid and protein catabolism in homeotherms. Phase I (11 days) was characterized by a decreasing rate of body-mass loss and a rapid increase in plasma f-hydroxybutyrate level, indicating body-lipid mobilization. During phase II (22 days), the rate of body-mass loss stabilized at a low level. Plasma concentration of 3-hydroxybutyrate peaked in the first half of phase II and then decreased. Plasma uric-acid level, an index of protein catabolism, increased during the second half. Resting metabolic rate of fasting geese was reduced by 38% below the pre-fast value, more than predicted from body-mass decrease alone. Phase III (3 to 4 days) was characterized by an increase in the daily rate of mass loss. Plasma concentration of uric acid increased markedly, while I-hydroxybutyrate values remained low and stable. Glycemia and total plasma protein level also started to fall. Greater Snow Geese did not tolerate fasting as long as larger birds, like penguins, probably because they were less efficient in sparing their protein reserves during phase II. Greater Snow Geese endurance of fasting may be limited by their use of flight, which ultimately limits their capacity to carry the large fat reserves required for prolonged fasting. Received 30 April 1991, accepted 13 January 1992. IN WILD BIRDS, fluctuations in food availability may impose fasting for more or less predictable periods of time. Energy requirements of small passerines allow them to tolerate fasting in winter for only 10 to 37 h before dying (Kendeigh 1945, Ketterson and King 1977), but large birds of prey may be deprived of food for 11 to 13 days and remain in good health (Hatch 1970, Garcia-Rodriguez et al. 1987). Even in the presence of food, some species may fast because feeding conflicts with other important activities. Red Jungle Fowl (Gallus gallus; Mrosovsky and Sherry 1980), most penguins and petrels (Croxall 1982, Cherel et al. 1988b), and many Arcticand temperate-nesting anatids (Korschgen 1977, Krapu 1981, Mainguy and Thomas 1985, Thompson and Raveling 1987, Ankney and Afton 1988, Parker and Holm 1980) greatly reduce their food consumption during egg laying and incubation. In these birds, only one parent incubates and it is not fed by its mate. Fasting endurance may have an adaptive value and be a key determinant of reproductive success in species facing a negative energy balance during nesting. The reproductive success of nesting geese depends largely on the quality of nest attendance by females during incubation (Murphy and Boag 1989). To reduce risks of predation and intraspecific nest parasitism, females stay on the eggs and feed little from laying to hatching (Ryder 1970, Ankney and MacInnes 1978, Raveling 1979, Aldrich and Raveling 1983, Prop et al. 1984, Mainguy and Thomas 1985, Thompson and Raveling 1987). Males do not incubate, but assume most of the territorial defense and also reduce their food intake (Inglis 1977, Stroud 1982). They lose weight, though to a much lesser extent than females (Ryder 1975, Ankney 1977, Owen and Wells 1979). In Lesser Snow Geese (Chen caerulescens caerulescens), females feed very little after completing laying. Without sufficient energy reserves to endure a long fast, some females do not complete incubation and may even die before its termination (Harvey 1971, Ankney and MacInnes 1978). Greater Snow Geese (Chen caerulescens atlantica) presumably also become anorexic during their 24-day incubation period (Lemieux 1959), although their nesting behavior is largely unknown. Despite the obvious importance of fasting in

DNA-DNA Hybridization Evidence of Phylogenetic Relationships among Major Lineages of Parus

Abstract: DNA-DNA hybrids were formed among 2 outgroups and 12 taxa of titmice and chickadees to estimate the genealogical relationships of the main Parus lineages. A complete matrix of reciprocal comparisons among seven parids and the Verdin (Auriparus flaviceps) indicated that the Blue Tit (P. caeruleus) and Great Tit (P. major) together form the sister group of the rest of the genus, and that the Bridled Titmouse (P. wollweberi) is more closely related to North American titmice than to the Old World crested tits. The DNA-hybridization data complement information from allozyme and mtDNA studies of closely related parids and provide historical insight into patterns of tit behavior.

Predation on the eggs and nestlings of Florida Scrub Jays

Abstract: ABsTRAcr.-We investigated nest predation in a population of Florida Scrub Jays (Aphelocoma c. coerulescens) at Archbold Biological Station, Lake Placid, Florida. Frequency of nest visits by investigators did not influence predation rates. Nest predation increased as the breeding season progressed and occurred most often during daylight hours. When seasonal effects were held constant, nestlings were depredated more often than eggs, and young nestlings were depredated more often than old nestlings. Several lines of evidence indicated that, for Florida Scrub Jays, diurnal snakes and birds were the most important nest predators, while nocturnal mammals were relatively less important. Late in the breeding season, pairs with helpers experienced less nest predation than pairs without helpers. This effect was primarily the result of reduced predation on nestlings. Received 17 June 1991, accepted 13 January 1992.

Living off the wax of the land: bayberries and yellow-rumped warblers

Abstract: Yellow-rumped Warblers (Dendroica coronata) and Tree Swallows (Tachycineta bicolor) are among a small group of birds in temperate North America that regularly eat waxy fruits. During the autumn, winter, and spring, these species feed extensively on fruits of the bayberry (Myrica spp.). Covering the pulp of these fruits is a solid, waxy material consisting primarily of saturated long-chain fatty acids. For most animals, saturated fatty acids are poorly assimilated ( 80%) of bayberry wax when fed berries recoated with radioactive wax tracers. Efficient fatty-acid assimilation extends to berries coated with cetyl palmitate, a common marine, saturated wax ester (> 90%). The fatty-alcohol moiety of the marine wax was assimilated with a much lower efficiency (<50%). A beeswax coating of the berries is assimilated with an efficiency of approximately 50%. Similar assimilation efficiencies of each wax are recorded for Tree Swallows feeding on recoated bayberries. Yellow Warblers (D. petechia) rejected recoated bayberries and exhibited little (<5%) lipid assimilation of radiolabeled lipids. Yellow-rumped Warblers possess several gastrointestinal traits that permit efficient saturated-fat assimilation. Among these are an apparent retrograde reflux of intestinal contents to the gizzard, elevated gall-bladder and intestinal bile-salt concentration, and a slow gastrointestinal transit of dietary lipids. These gastrointestinal traits permit efficient assimilation of saturated fatty acids on bayberry fruits and may allow these small passerines to maintain more northerly wintering ranges than closely related species. Received 24 May 1991, accepted 5 November 1991.

Frequency Variation in Songs of Black-Capped Chickadees (Parus Atricapillus)

Abstract: -Recordings of dawn singing by male Black-capped Chickadees (Parus atricapillus) show that each individual sings its fee-bee song at a wide range of frequencies. Males tend to repeat songs at a given frequency but on average after every 41 ? SE of 8.8 songs a male shifts the frequency of its song by a statistically significant amount (?80 Hz). During any given morning, males may appear to shift among a limited set of discrete frequencies, but over longer time periods intermediate frequencies also are sung. These results suggest that chickadees can vary the frequency of their song more or less continuously over the species' frequency range. When songs of one of three widely spaced frequencies (recorded in previous years) were played back, males replied with songs that had approximately the same frequency as the playback song. Thus, frequency shifting appears, at least in part, to be a form of song matching. These results add to a growing body of evidence that some species with single-song repertoires have evolved effective matching strategies through manipulation of the frequency of their song. Received 14 June 1991, accepted 20 January 1992. THE MAJORITY of songbirds possess multisong repertoires, in which song types can be easily distinguished from each other on the basis of several frequency and temporal features. There has been considerable effort to understand the interand intrasexual selective pressures favoring the evolution of multisong repertoires (e.g. Kroodsma and Miller 1982, Searcy and Andersson 1986). In contrast, the conditions that predispose species to maintain single-song repertoires have received comparatively little attention. By single-song repertoires, we mean those in which songs may vary in a graded fashion (e.g. longer or shorter), but cannot be divided into groups by discontinuities in any single parameter or combination of parameters. Species with single-song repertoires may show little variation in song structure because of some advantage to stereotypy, for example, because low variation within and between males in a given area aids the recognition of dialects (e.g. Baker and Cunningham 1985). Alternatively, relatively subtle variations in song structure may serve functions that, in a repertoire species, would be served by abrupt changes in song type. For example, variation in the frequency of the songs of Kentucky Warblers (Opornis formosus; Morton and Young 1986) and Harris' Sparrows (Zonotrichia querula; Shackleton et al. 1991) allow males to match the frequency of each other's songs as a signal in territorial contests. In species with song types, this function is served by males matching each oth-

Bill color, reproduction and condition effects in wild and domesticated Zebra Finches

Abstract: Bill-color variability has the identical range and similar distributions in free- living Australian Zebra Finches (Taeniopygia guttata) and their wild-type domesticated de- scendants. Individual differences in bill color exist among adults of both sexes, both in nature and captivity. In laboratory birds, bill color changed over the course of the five-week breeding cycle, with lowest bill-color scores expressed at the end of the cycle. Longer-term patterns included a gradual decline of bill color over the course of multiple clutch attempts, followed by a rapid increase when resources for breeding were withdrawn. Among laboratory males, survivorship was clearly independent of bill color. Among females, bill color changed more rapidly in birds that subsequently died than in those that survived a two-year breeding experiment. High rates of reproduction were significantly associated with decline of male bill score, but not female bill score. The bill-color scores of laboratory males maintained on supplemented and basic seed diets for eight weeks did not diverge. Crowding of laboratory birds was associated with decreased bill color. For birds in nature, bill color tended to decline over the breeding season. Bill color of captive wild birds became more red over a six-week period when birds were fed ad libitum on the laboratory diet. Data for both laboratory and wild birds indicate that reproduction is associated with a decline of bill color in both sexes. Results of diet experiments were inconclusive, but helped to establish that the range of bill colors displayed by domesticated birds is similar to that encountered in nature. Our results, when considered in light of previous findings, suggest the possibility that bill color has different costs and benefits for the sexes and that genetic and/or physiological constraints prevent optimal phenotypic expression of bill color in Zebra Finches. Received 4 June 1990, accepted 21 July 1991.

Reproductive Implications of Egg-Size Variation in the Black Brant

Abstract: -We analyzed variation in egg size of Black Brant (Branta bernicla nigricans) in relation to clutch size, laying date, female age, year, and position in the laying sequence. A total of 3,478 eggs was measured over three years. Egg size increased with clutch size and female age, and decreased with laying date, year, and position in the laying sequence. We did not detect a negative phenotypic correlation between clutch size and egg size. However, overlap in total clutch volumes for clutches of different sizes indicated trade offs occurred among individuals with comparable investments in their clutches. Received 1 October 1991, accepted 30 March 1992. THE COMBINATION of clutch size and egg size determines the total energetic investment in clutch formation by a laying female. Egg size may affect female fitness through its effects on initial size, early growth and survivorship of hatchlings (Cole 1979, Ankney 1980, Thomas and Brown 1988, Sedinger and Flint 1991), whereas clutch size is related to fitness via its effect on the potential number of offspring produced (Lessells 1986). Arctic-nesting geese rely heavily on stored lipid and protein reserves for egg production and incubation (Ankney and MacInnes 1978, Raveling 1979, Ankney 1984). Thus, nutrients available for a clutch are limited and at least partially predetermined when geese arrive on the breeding grounds. This limitation on reproductive investment, combined with the fitness advantages of both large clutches and large eggs, creates the potential for both ultimate and proximate trade offs between clutch size and

Effects of food abundance and male parental care on reproductive success and monogamy in tree swallows

Abstract: We examined the roles of food abundance and male parental care in the main- tenance of monogamy in Tree Swallows (Tachycineta bicolor). Mated, male Tree Swallows were removed from territories to simulate the lack of male parental care that would be incurred by secondary females. Removals took place in lakeshore and roadside habitats in central Alberta, Canada. Insect sampling over three breeding seasons indicated that the lakeshore had greater biomass of insects than the roadside during egg laying, but there was no difference during the nestling period. Both our male removal experiment and natural cases of polygyny suggested that loss of male parental care had little effect on reproductive success or survival of females or their offspring. Unaided females increased their per-capita nest-visit rate in two of three years, so the rate of visitation per nestling did not differ significantly between unaided females and both the male and female at control nests. Control females at the lakeshore produced more fledglings than control females at the roadside. This difference in productivity was due to earlier laying and larger clutches at the lakeshore than at the roadside and not to differences in brood reduction or insect abundance during the nestling period. In both habitats, male parental care was relatively unimportant to female reproductive success and, therefore, within a given habitat secondary females did not incur a reproductive cost. All natural cases of polygyny occurred at the lakeshore. We suggest that polygyny occurred at the lakeshore, and not at the roadside, because food abundance was greater during laying at the lakeshore, and this allowed secondary females to lay more eggs and produce more fledglings than females mated to monogamous males at the roadside. Received 11 March 1991, accepted 10 February 1992.

Roles of egg mass and incubation pattern in establishment of hatching hierarchies in the blackbird (Turdus merula)

Abstract: ABSTRAC'r.--In many species of altricial birds, eggs hatch asynchronously and the last nestling to hatch may starve to death or be killed by its older and larger siblings. Lack (1947) suggested that hatching asynchrony was adaptive because it facilitated the reduction of brood size if food was scarce after hatching, but there are many other hypotheses to explain hatching asynchrony. All adaptive hypotheses rely on the assumption that adults can control the degree of hatching asynchrony of their broods through their incubation behavior; starting incubation before laying is complete should produce asynchronous hatching. Parents potentially could enhance size hierarchies by laying a smaller egg as the last of the clutch, or reduce size hierarchies by laying a large last egg, so it has been suggested that intraclutch variation in egg mass could be adaptive by modifying hatching hierarchies. In this paper on the Blackbird (Turdus merula), I test the assumption that incubating females can control the hatching asynchrony of their broods, and assess the relative importance of hatching asynchrony and egg mass in the establishment of hatching hierarchies. Within clutches, the first egg tended to be the lightest and the penultimate egg the heaviest, but the last-laid egg was similar to the mean for the clutch. Incubation often started before the last egg was laid and, generally, eggs hatched in the order in which they were laid. Females started incubation earlier with respect to the last-laid egg as clutch size increased and the breeding season progressed, causing an increase in hatching asynchrony with clutch size and, in one year, laying date. Incubation apparently increased gradually through the laying sequence, rather than starting abruptly with the laying of a specific egg. Hatching asynchrony explained up to 77% of the variation in mass among siblings, while egg mass never accounted for more than 9%. Thus, hatching hierarchies primarily reflect hatching asynchrony, not egg mass. There was no effect of egg mass on the incubation period, so that egg mass did not influence hatching asynchrony. I conclude that in the Blackbird, females control the hatching asynchrony of their broods, and hatching asynchrony is far more important than egg mass in establishing hatching size hierarchies. Overall, variation in hatching asynchrony in the Blackbird is consistent with Lack's hypothesis of adaptive brood reduction, but cannot disprove other adaptive hypotheses. Received 11 March 1991, accepted 4 February 1992.

Structure of Turning in Airborne Rock Dove (Columba livia) Flocks

Abstract: -We describe a nonstereo, three-dimensional photographic technique to study the turning movements of flocks of semidomestic Rock Doves (Columba livia). The method permits sequential examination of an individual's position and flight path. The birds in flocks we studied with this technique did not maintain fixed positions. Birds continually repositioned themselves during a turn. Such repositioning of individuals may be more significant in the predator-evasion function of cluster flocks than for aerodynamics. Received 8 February 1991, accepted 13 January 1992. THE WHEELING and turning maneuvers of birds flying in coordinated cluster flocks are commonly observed phenomena (Heppner 1974). The advantages incurred by birds within an organized flock structure may include aid in location and efficient exploitation of food (Murton 1968, Krebs 1973), detection of predators (Powell 1974, Siegfried and Underhill 1975, Kenward 1978), and use of neighbors as a physical screen from danger (Pulliam 1973, Treis-

Reproductive Patterns and Social Organization of the Communal Guira Cuckoo (Guira Guira) in Central Brazil

Abstract: ABsTRACr.-The communal breeding system of the Guira Cuckoo (Guira guira) was studied near Brasilia, Brazil. Guiras occurred in groups of 2 to 13 adults (mode of 6) in the 86 nests observed. Communal clutch size was correlated with group size, an indirect indication that more birds contribute to the clutch in larger groups. Clutch size varied from 4 to 20 eggs, but usually fewer eggs were incubated than were laid, since egg tossing by the adults was common. The temporal patterns of egg laying and egg loss, while generally similar to those of other crotophagines, differed in some ways. Egg losses occur at any time after laying starts. Losses may occur after several eggs have accumulated in the nest, may affect only part of the clutch, and may happen close to, or during, the hatching of chicks. Only 26% of eggs developed into fledglings; high mortality rates for eggs and chicks are due to several causes. An individual may pay a price for group membership through a lowered short-term reproductive success; however, long-term data are needed to clarify individual lifetime benefits associated with communal breeding in this species. Received 18 June 1991, accepted 20 February 1992.

Age-Related Effects of Testosterone, Plumage, and Experience on Aggression and Social Dominance in Juvenile Male Satin Bowerbirds (Ptilonorhynchus violaceus)

Abstract: ASSTRACT.--We investigated the relationship between age and dominance in the Satin Bowerbird (Ptilonorhynchus violaceus) to understand why young males delay maturation. Testosterone implants were used to experimentally advance the expression ofadult characteristics in juvenile-plumaged males. Testosterone implants increased both aggression a d dominance among juvenile-plumaged males. In the year following implantation, treated males molted into full adult plumage and maintained their dominance over controls at feeding sites even though their implants were probably empty. Despite the changes in circulating androgens, aggression, and plumage brought on by the testosterone treatment of juvenile-plumaged males, age-related ifferences remained in aggression and social dominance between the treated and untreated birds. These age effects are consistent with the hypothesis that male experience inmale aggressive encounters plays an important role in determining dominance relationships and, ultimately, affects the development of male adult-plumaged characters. Received 12 September 1990, accepted 13 January 1992.

Pair Composition and Reproductive Success across a Hybrid Zone of Carrion Crows and Hooded Crows

Abstract: AI•sTP,•CT.--The Carrion Crow (Corvus corone corone) and the Hooded Crow (C. corone cornix) have parapatric ranges in Europe with narrow areas of hybridization. Reproductive biology of populations of Carrion and Hooded crows and hybrids is described for four areas in northern Italy. Nonrandom mating was observed in a hybrid zone. Homogamic pairs were observed more frequently than expected by chance. Data on clutch size and reproductive success were analyzed for Carrion Crows and Hooded Crows in allopatry, and for parental and hybrid phenotypes in a hybrid zone. Clutch size did not vary across the hybrid zone. Pairs with Hooded Crow females in the hybrid zone produced significantly more chicks than those with hybrid females. The number of chicks recorded from Carrion Crow females was higher than for hybrid females, but not significantly. Significant variation was observed for the effect of the male's phenotype on reproductive success due to the comparatively high reproductive success of Carrion Crows in the area of allopatry. No significant difference in the reproductive success was observed in the hybrid zone between pairs containing only parental phenotypes and pairs containing at least one hybrid. Carrion Crows in allopatry produced more fledglings than Carrion Crows in the hybrid zone, whereas Hooded Crows in allopatry had a reproductive success very similar to that of Hooded Crows in the hybrid zone. Our results do not support the dynamic-equilibrium model but are compatible with the bounded-hybrid-superiority model. The hybrid zone studied coincides with an "ecotone" between the alpine valleys and the intensively cultivated plain. We conclude that the maintenance of parapatric distributions of the two morphs is due mainly to ecological factors. The hybrid zone could be considered the narrow belt in which environmental features are such that hybrids are not less fit than parental individuals, its narrowness being caused by the steepness of the environmental gradient crossing it. The nonrandom mating observed could result from heterogeneous phenotype dispersion which, in turn, reflects differential habitat selection in the hybrid zone. Received 22 April 1991, accepted 10 January 1992.

Copulation patterns and sperm competition in the polygynandrous Smith's longspur

Abstract: ABSTRACr.-In a color-marked population of Smith's Longspurs (Calcarius pictus) near Churchill, Manitoba, I recorded the timing and frequency of copulatory and mate-guarding behavior in relation to breeding season and time of day. Longspurs formed mating associations best described as female-defense polygynandry. Females copulated with two (rarely three) males (designated alpha, beta and gamma according to mating order), and each male with one to three females for an estimated average of 365 (range 214-629) copulations per clutch. This is one of the highest copulation rates reported in birds. More than 99% of all copulations were preceded by female solicitation but only about one-third of all solicitations were followed by mounting. Copulations began three to five days before clutch initiation and ceased just before or shortly after the penultimate egg was laid. Female copulations with alpha males peaked at clutch initiation at a rate of 5.3 copulations per hour. The copulation rate of beta and gamma males peaked two days after laying was initiated at 2.6 copulations per hour. All copulations probably occurred within the female's fertilization period and, thus, potentially could have resulted in fertilization of eggs. Copulations were most frequent during morning and late evening; they were rare during the afternoon. This diurnal pattern also corresponds to the period when inseminations were most likely to fertilize eggs. During the copulation period, males guarded their mates by closely following females and chasing away intruding males. Guarding and chasing by alpha males were most intense just before the first egg was laid, while guarding by beta and gamma males peaked on the day the third egg was laid. As with copulations, mate guarding and chasing were most intense in the morning and evening. The occurrence of multiple mating by females and the lack of territorial behavior in males suggests that frequent copulations in this species evolved as an adaptation to sperm competition. Received 24 April 1991, accepted 13 January 1992.