Showing papers in "The Condor in 1985"

Reproduction of ferruginous hawks exposed to controlled disturbance

Abstract: -The Ferruginous Hawk (Buteo regalis) is a conspicuous grassland bird that is sensitive to human disturbance. In 1978 and 1979, we studied 62 nesting pairs and recorded their behavior and nesting success. At 24 of these nests, we daily created disturbances designed to simulate those associated with land development on western rangelands. The other nests were not disturbed. Treated nests and control nests differed significantly (P < 0.05) in the number that successfully fledged young. Thirty-three percent of the disturbed nests were deserted by the adults, although our presence in the vicinity of the nest was brief. Those disturbed nests that were successful fledged significantly fewer young (P < 0.05) than undisturbed nests. Based on our cumulative data, adults did not flush 60% of the time if our activities were more than 120 m from the nest and 90% of the time if they were more than 250 m from it. Accordingly, for intermittent and brief human disturbance during years when prey are abundant and Ferruginous Hawks are in good physiological condition, we suggest that a minimum buffer zone of 0.25 km around the nest is sufficient to prevent nest desertion by at least 90% of the population. Buffer zone should be expanded in years when prey are scarce, i.e., when the hawks appear to be less tolerant of disturbance. The Ferruginous Hawk (Buteo regalis) is seriously affected in some areas by land development and, consequently some populations of the species are apparently small and may be declining. Reflecting this trend, the species has been on the Audubon Blue List since the list was established in 1971 (Tate and Tate 1982). A minimum number of breeding pairs was recently estimated at 2,810-3,590 over the entire range (M. Call, unpubl., U.S. Bureau of Land Management, Denver, CO, 1980). Ferruginous Hawks are particularly sensitive to human activity (Olendorff and Stoddard 1974, Fyfe and Olendorff 1976, Woffinden and Murphy 1977) and are prone to desert their nests if disturbed during incubation. Nonetheless, the species can respond well to management (White 1974, Porter and White 1976, Murphy 1978) so that it may be possible to adjust human activities to minimize ecological disturbance to it. Kennedy (1980) suggested such an approach in her assessment of conflicts concerning raptors and land use. It is becoming increasingly difficult to maintain critical wildlife habitat as the multiple-use demands on land intensify. The amount of disturbance that sensitive species will tolerate must be measured so that land management plans can be devised that are compatible with the species' needs. Our objectives were to determine how Ferruginous Hawks respond to disturbances, the levels of disturbances they will tolerate, and the size of buffer zones neede by disturbed pairs to maintain a level of nesti g success and productivity similar to those of undisturbed pairs. To accomplish this, we considered the natural tolerance thresholds of the species, the relationship of tolerance to prey availability, and the nesting history of the po ulation as related to disturbance. Most previous buffer zone recommendations from management agencies and the scientific community have been based primarily on best guess or anecdotal knowledge. Estimates of the sensitivity of Ferruginous Hawks, or raptors in general, to human disturbance were mainly obtained from observations made during studies of their breeding ecology. A significant exception is the Bald Eagle (Haliaeetus le cocephalus) for which considerable data were collected to aid development of sound management policies (cf. Grier 1969, Gerrard and Gerrard 1975, Mathison et al. 1977). Stalmaster and Newman (1978) examined the effects of some controlled disturbances on nonnesting Bald Eagles, but few other attempts hav been made to identify, quantify, and control variables that cause nest desertion. METHODS AND STUDY AREA We conducted our study throughout the Raft River Valley (42?N, 1130W), Cassia County, sou h-central Idaho (Fig. 1). The northern boundary of the valley opens onto the Snake

Reliability of singing bird surveys: effects of song phenology during the breeding season

Abstract: Essais de determination de la densite de population de Troglodytes aedon dans l'Ohio central par denombrement des chants: cette methode n'est nullement precise pour obtenir la densite relative

The Timing and Energetic Consequences of Egg Formation in The Adélie Penguin

Abstract: -To study the timing of egg formation in the Adelie Penguin (Pygoscelis adeliue), we gave 150 females an oral dose of Sudan black dye before they laid their eggs. This lipophilic dye is incorporated into yolk synthesized on the day of dosing and deposited on the developing ovum as a blue layer. First, second, and third fresh eggs laid by dosed birds were collected. Analysis of the timing of egg formation revealed that rapid yolk deposition (RYD) on the first ovum began 10-l 2 days prior to cessation of feeding. Second and third yolks were initiated sequentially at 3-day intervals. The total time necessary for RYD was 14-17 days, and was followed by a 5to 7-day lag period between yolk completion and laying. In total, 19-24 days were required to produce each egg. Within clutches, second and third eggs were smaller than the first egg, owing to reduced albumen content, while yolk mass remained relatively constant. We determined the daily energy, protein, and lipid input into a clutch and estimated that the use of a female’s body reserves during a 12-day fast requires 307 g of muscle tissue. Of this, approximately 123 g of muscle (40%) are required to produce the 24 g of protein contained in egg components deposited during the fast. Both the long lag period and the 3-day interval between laying eggs may be adaptive in reducing the daily protein demand for egg production. The cost of egg production in wild birds has been the subject of considerable attention (see Ring 1973, Ricklefs 1974, and Murton and Westwood 1977, for reviews), but the importance of nutrient requirements for egg formation in such species has remained elusive and poorly understood. Egg formation in domestic hens, selected for rapid egg formation and prolonged productivity, cannot represent the avian model for this function, particularly when considering the temporal and energetic constraints attendant on most wild species. Our recent research (Grau ‘1984; Astheimer, in press) indicates that the process of egg formation is not evolutionarily static; there appear to be many species-specific variations which involve modifications both in the timing of formative events and in the rates of material deposition, either within the follicle or in the oviduct. Such differences would naturally affect any energy assessment of the daily production cost of a clutch. We chose to investigate the timing of egg formation in the AdClie Penguin (Pygoscelis adekze) to clarify the dynamics of egg production in a seabird that lays a two-egg clutch. We had previously concentrated on Cassin’s Auklet (Ptychoramphus aleuticus), which provided a simple model for egg formation of a single-egg clutch (Astheimer et al. 1980). An attempt to study this problem in eggs of the Fiordland Crested Penguin (Eudyptes pachyrhynchus) was limited to collection of single eggs of this species’ two-egg clutch owing to permit restrictions (Grau 1982). A preliminary study showed AdClie Penguins to be tractable experimental subjects (Grau and Wilson 1980) and, moreover, their highly synchronized reproductive timetable was delineated by distinct breeding events that could be related to the timing of egg formation. AdClie Penguins nest colonially on exposed islands and peninsulas in antarctic waters. Spring arrival often requires that the penguins cross many kilometers of sea ice on foot. After a brief prelaying period, during which courtship and nest construction occur, the female normally lays a twoegg clutch with a 3-day interval between eggs. Following clutch completion, she departs the rookery, ending her twoto three-week fast. Our purposes here were to (1) determine the timing of egg formation, (2) relate timing to the sequence of breeding events before laying, (3) compare differences within clutches in timing and egg composition, and finally, (4) estimate the daily and total nutrient costs of egg production for a female Adelie Penguin.

Song Dialects of White-Crowned Sparrows: Historical Processes Inferred from Patterns of Geographic Variation

Abstract: -We described geographic variation in the syllabic structure of the song of White-crowned Sparrows (Zonotrichia leucophrys nuttalli) resident in coastal California. We identified six large and relatively homogeneous populations that differed discretely at one locus in the song, the complex syllable, and have called these "dialect" populations. Two "superdialects" were also identified on the basis of two other loci in the song, the introduction and the ending. Using another part of the song, the simple syllable locus, we also identified large-scale geographic clusters of similarity that were moderately concordant with dialect variation. From the patterns of geographic variation shown by the four song loci, we hypothesize that our study area was colonized by two ancestral populations. The existing song populations are therefore interpreted to be in secondary contact. Relatively narrow zones of "overlap" at dialect borders are identified and their widths estimated. Application of cline theory to the data suggests that 100-200 years have elapsed since secondary contact. One can approach the study of local geographic variation in cultural patterns, such as avian song dialects, in the same way that an evolutionary biologist approaches the study of geographic variation in morphological characters or gene frequencies (Cavalli-Sforza and Feldman 1981). An important difference is that, in many bird species, variation in song results from learning, not from genetic transmission. Recent surveys indicate that cultural inheritance of song is the rule for most oscine birds-nearly half of the world's avian species (Kroodsma and Baylis 1982). In this report, we apply a conceptual framework from evolutionary biology to interpret the spatial distributions of song variants in a population of birds. This application is appropriate because we hypothesize that in songbirds, as in humans, culturally transmitted traits affect the course of genetic evolution (Wyles et al. 1983). For long-term research on the biological significance of song variation, it is important to obtain a comprehensive description of the microgeographic variation in song among a series of contiguous populations. Such information provides a basis for understanding existing patterns of genetic differentiation of the populations, behavioral responses of both sexes to field and laboratory experimental manipulations (such as playback of male song of different dialects), and patterns of dispersal within and between dialects (Baker 1975; Baker and Mewaldt 1978; Payne et al. 1981; Petrinovich and Patterson 1981, 1982; Baker et al. 1982; Baker 1983; Tomback et al. 1983). Moreover, one may be able to suggest explanations of how song populations are related to one another in an historical sense (Baptista 1975). We as ume that populations with similar vocal patterns are more closely related than those with different vocal patterns, and that vocalizations can therefore be used to recontruct patterns of colonization (Baptista 1975, Mundinger 1975, Baptista 1977, Baptista and King 1980). Observations of zones of intergradation and hybridization, geographic variation, and clines have provided important information for interpreting evolutionary processes (Mayr 1963, Endler 1977), and our appr ach to interpreting song variation derives from this tradition. By analyzing song variation within and among the dialects of White-crowned Sparrows (Zonotrichia leucophrys nuttalli) occupying the Point Reyes Nat onal Seashore, we have developed a hypothetical model of how the dialects were derived. Because these populations occupy natural habitat in relatively undisturbed conditions within the pr tected boundaries of a National Seashore, our description of the geography of song may be of value in understanding the dynamics of song variation, both in the immediate d distant future. Evaluation of changes in the trait should provide an informative windo for observing the process of cultural evolution i avian communication (Jenkins 1978; Slater and Ince 1979; Ince et al. 1980; Mundinger 1980, 1982; Payne et al. 1981).

Avian Use of a Desert Riparian Island and Its Adjacent Scrub Habitat

Abstract: -A riparian bird community in central Arizona contributed from 23 to 33% of the birds along the adjacent desert washes, and from 7 to 15% of the birds in the adjacent desert upland. Conversely, the desert bird community contributed only from 1 to 1.5% of the birds in the riparian island. Bird density ranged from 336 to 446 birds/40 ha in the riparian core and edge in 1981 and 1982. Bird density in the adjacent desert decreased with distance from the edge of the riparian island to a low of 10 1 birds/40 ha in 198 1, to 137 birds/40 ha in 1982, in the segment 600 to 1,000 m from the riparian edge. Riparian woodlands in the southwestern United States are extremely important to bird populations (Carothers et al. 1974, Stamp 1978, Ohmart and Anderson 1982. These woodlands are often considered isolated habitat islands, yet adjacent areas may be important in determining riparian bird population densities and composition (Stevens et al. 1977, Shurcliff 1980, Szaro 1980). Neighboring areas can include many different vegetation types, each with its own complement of breeding birds that are potentially capable of competitively restricting riparian birds (Carothers et al. 1974). Differences in availability of food and nest sites in adjacent habitats may further affect riparian bird density and species richness, even in the same riparian type (Goldberg et al. 1979). Conversely, riparian birds may influence bird population densities and species composition in the environs (Conine et al. 1978, Hehnke and Stone 1978, Wegner and Merriam 1979). We sought to determine the extent to which the bird communities of a riparian island and the surrounding desert scrub influence each other. We examined several questions concerning the interaction between the two communities: (1) which bird species, if any, are found exclusively in either habitat? (2) what is the contribution, in terms of densities and species richness, of the bird populations in either habitat to each other? (3) how far do riparian or desert birds venture into other habitats? and (4) are there any differences in summer versus permanent resident use of the habitats? Answers to these questions will advance our understanding of the role that riparian habitat islands play in determining bird community structure in the arid southwestern United States. STUDY AREA We conducted our study on the Tonto National Forest on Queen Creek, about 3.7 km upstream from the mouth of Whitlow Canyon and about 16 km west of Superior, Arizona. The area consists of a 15-ha stand of Goodding willow (Salix gooddingii) and salt cedar (Tamarix pentandra), surrounded by Sonoran Desert scrub (Szaro and DeBano 1985). The riparian stand is rectangular, approximately 350 m by 450 m. A border of vegetation approximately 35 m wide along the edge of the stand is composed of salt cedar, seep willow (Baccharis glutinosa), and velvet mesquite (Prosopis julzjlora). Two washes extend northward, perpendicular to the long edge of the stand. Their vegetation primarily consists of catclaw (Acacia greggii), velvet mesquite, desert hackberry (Celtis pallida), creosote bush (Larrea tridentata), seep willow, and foothill palo Verde (Cercidium microphyllum). On the upland benches, which extend from the riparian area parallel to the washes, the vegetation is foothill palo Verde, saguaro cactus (Cereus giganteus), jumping cholla (Opuntiafulgida), jojoba (Simmondsia chinensis), Engelmann prickly pear (0. phaeacantha), creosote bush, teddy bear cholla (0. bigelovii), and ocotillo (Foquiera splendens). For a more complete description of the vegetation, see Szaro and DeBano (198 5).

Reproduction in zebra finches: hormone levels and effect of dehydration

Abstract: -Zebra Finches (Poephila guttata) of arid Australia can breed continuously under favorable conditions. During droughts, however, breeding ceases but is said to begin again immediately after rain. We found that testis size in breeding birds did not change during, or between, reproductive cycles. Luteinizing hormone (irLH) levels in plasma, however, were significantly higher in males during early incubation (1.25 ng/ml), and in females during courtship (0.89 ng/ ml), than during other parts of the reproductive cycle. Plasma levels of the sex steroids were highest (1.06 ng/ml for androgen in males, 0.32 ng/ml for estrogens in females) at the same time that irLH levels were highest. Wild-caught Zebra Finches had, at capture, testes similar in size to those of aviary-breeding Zebra Finches, but after three weeks of dehydration (1 ml water/bird/week), testis size was significantly smaller and hematocrit was significantly higher: 54% vs. 50% for birds given unlimited access to water. When dehydrated birds were given unlimited access to water, testes grew significantly. Access to green grass or exposure to high relative humidity (85%) augmented the effects of the water on testis size. Spermatogenic activity in some dehydrated birds was high despite small gonad size; however, interstitial tissue was poorly developed, and plasma levels of sex steroids and irLH were low. We suggest that Zebra Finches normally maintain gonadal tissue in a functioning state unless severely dehydrated. Relief from dehydration is a necessary, but not sufficient, condition for the full expression of reproduction. For species that do not live in temporally uniform environments, the timing of reproduction can be a critical element in reproductive success. In many temperate zone birds, reproductive activity begins during the spring, when increasing daylength provides a dependable cue that indicates the approach of conditions favorable for reproduction (see reviews in Lofts and Murton 1968, Farner 1970, Farner and Lewis 1971, Wingfield and Farner 1980). Compared to daylength, other environmental cues that may play a role in controlling the timing of reproduction have received little attention (Moreau 1950, Marshall and Disney 1957, Marshall 1970, Immelmann 1971, Wingfield 1980, Earle 1981, Storey and Nicholls 1982). In some habitats, daylength may not be a reliable cue for reproduction because the onset of other favorable conditions is independent of the changes in daylength. Desert birds, for example, may encounter suitable conditions for reproduction only for brief periods after rainfall, and in such species rapid initiation of reproduction in response to rainfall, regardless of daylength or season, may maximize reproductive success. Such breeding in response to rain apparently occurs in the Zebra Finch (Poephila guttata, syn: Taeniopygia guttata castanotis) native to the arid interior of Australia. The reproductive state of Zebra Finches is not influenced by daylength (Marshall and Serventy 1958, Oksche et al. 1963, Sossinka 1975). In the mesic parts of their range, or in areas receiving agricultural irrigation, Zebra Finches breed year-round, except in the coldest winter months, with peaks in nesting attempts occurring in spring and in autumn (Frith and Tilt 1959, Kikkawa 1980). In arid central Australia, however, the species breeds following the irregular rains, regardless of the time of year (Immelmann 1965). Davies (1977), in a two-year study of Zebra Finches in Western Australia, found birds breeding in every month except March, April, and August, and suggested that both rainfall and temperature were important in the initiation of breeding. Immelmann (1963, 1965) reported that Zebra Finches copulated within a few hours of the beginning of the first rain following several months of drought, and began nesting and egglaying within one week. Zebra Finches are capable of producing many offspring under favorable conditions because (1) both members of the pair participate in nest building (Immelmann 1963), (2) a pair will nest repeatedly as long as conditions remain favorable (Ser-

Foraging and Habitat Relationships of Insect-Gleaning Birds in a Sierra Nevada Mixed-Conifer Forest

Abstract: -Foraging habits and relative abundances of 12 birds comprising the insect-gleaning guild in a Sierran mixed-conifer forest were studied during two breeding seasons to determine: (1) foraging habitat preferences, (2) the extent to which species differ in their use of various components of the foraging niche, (3) patterns of relative abundance vs. niche breadth, and (4) differences between resident and migrant species. Comparisons of proportional availability and bird use of foliage height classes and tree species showed that tree species and, to a lesser extent, heights were used selectively by the guild. Incense-cedar (Calocedrus decurrens) was consistently avoided by all species; other tree species were generally used in a complementary manner by different birds. Of four measured components of foraging niche, the use of foraging site (consisting of air or tree part) showed the greatest difference between species, followed by tree species, foraging techniques, and foraging height. We found no correlation between niche breadth and species abundance for all guild members; however, a significant positive correlation existed for the five resident species. Resident and migrant species groups showed few fundamental differences in foraging patterns, except that migrants tended to use a greater proportion of deciduous foliage than residents. Our results suggest that to provide for this guild, land managers should maintain natural levels of tree species diversity in the mixed-conifer forest type. Many studies have shown that syntopic insectivorous birds differ in their methods of foraging. In forested habitats, birds tend to use different foraging techniques, foraging sites, tree species, and heights. The relative importance of these foraging niche components in distinguishing species has received less attention. Differences in importance of niche components reported in previous studies may reflect either real differences that exist in different habitats and geographic areas (Balda 1969), or incomplete analysis of all potentially relevant factors (Holmes and Robinson 1981). In particular, the importance of differential plant species use has not been fully appreciated (Holmes and Robinson 1981). Additional information is needed before sound generalizations can be made regarding patterns of differentiation among insect-gleaning birds. In managed forests, plant species composition and vegetation structure may be altered by logging, other silvicultural activities, and disruption of natural fire regimes (Kilgore 1971, Franzreb and Ohmart 1978, Szaro and Balda 1979). Identification of habitat preferences of forest birds can suggest recommendations to mitigate impacts of manipulation. The mixed-conifer forest of the Sierra Nevada, California, supports a large number of arboreal insectivorous birds (Verner and Boss 1980). We studied foraging substrate preferences, foraging behaviors and relative abundances of the 12 most common members of an insect-gleaning guild. We sought to: (1) compare the guild's use of tree species and vertical foliage layers with the availabilities of these habitat components; (2) describe and compare foraging sites and techniques used by each species; (3) evaluate the relative importances of foraging heights, tree species use, foraging sites, and foraging techniques in differentiating species ecologically; (4) determine if resident and migrant species differed in their foraging and abundance patterns; and (5) suggest management recommendations to mitigate the effects of habitat manipulation on members of the insect-gleaning guild.

Prospecting for nest sites by cavity-nesting ducks of the genus Bucephala

Abstract: We studied the pattern of post-laying visitation of nest sites by non-nesting females in three species of cavity-nesting ducks, the Common and Barrow's goldeneyes (Bucephala clangula and B. islandica) and the Bufflehead (B. albeola). Nests were visited from mid-June to mid-July when most nesting females either had hatched their clutches or were finishing incubation. Females often visited more than one nest site and each nest site could be visited by several birds. Observations of marked individuals and body measurements of trapped birds show that most visiting females were either yearlings or failed breeders. These females always visited nest sites in intraor inter-specific groups, and exhibited typical vocalizations and flight patterns. We propose that these females were "prospecting" for nest sites in preparation for the next breeding season. We could not find any detrimental effects of prospecting on incubating females. We also discuss the evolutionary significance of prospecting behavior and its relationship to delayed maturity and nest-site availability for both cavityand groundnesting North American ducks. Selection of an appropriate nest site has an important influence on breeding success in waterfowl. In ground-nesting ducks, nest success and predation rates on nests have been related to both the location and the type of cover near the nest (Schrank 1972, Lokemoen et al. 1984). In cavity-nesting ducks, competition for nest sites can be intense (e.g., Jones and Leopold 1967), and nest-site location has been shown to influence reproductive success in the Common Goldeneye (Bucephala clangula; Dow and Fredga 1983). Although much quantitative information is available on nest-site characteristics for many species of ducks (e.g., Bengston 1972, Lokemoen et al. 1984), little is known about the behavioral mechanisms used in nestsite selection. Most ducks search for nest sites immediately before nesting (Bengston 1972, Bellrose 1976, Palmer 1976). In the genus Bucephala, however, females have been reported to search for nest sites at the end of the summer, presumably in preparation for the next breeding season (Grenquist 1963, Bengston 1966, M. Jackson in Bellrose 1976, Cramp and Simmons 1977). This behavior has often been called "nest prospecting," to distinguish it from the more usual form of nest searching at the beginning of the breeding season. The unusual timing of nest searching in Bucephala is interesting for three reasons. First, all three species of Bucephala nest in tree cavities, and nest sites are often limited (Erskine 1972, Savard 1982). It is possible that nest searching in advance of the next breeding season has evolved in response to the scarcity of suitable nest sites. Second, despite the above reports of "end of the season" nest searching in Bucephala, few data are available. We know of only one detailed study of nest searching in a hole-nesting duck (Patterson and Makepeace 1979, Patterson 1982, for the Common Shelduck, Tadorna tadorna). Third, Grenquist (1963) suggested that nest searching by female goldeneyes at the end of the breeding season might cause nest desertion by incubating females. This potential cost to incubating females has received little attention in previous studies. The objectives of our study were, therefore: (1) to quantify and compare the late season nest visitation patterns of three species of cavity-nesting ducks, the Common and Barrow's goldeneyes (Bucephala islandica) and the Bufflehead (B. albeola), (2) to consider the hypothesis that females were "prospecting" for nest sites for the following year, and (3) to examine potential costs of this activity to both incubating and visiting females.

A Comparison of Transects and Point Counts in Oak-Pine Woodlands of California

Abstract: Comparaison des resultats de la methode des quadrats et de la methode de denombrement ponctuel pour la determination de la richesse specifique et de la densite de population des oiseaux dans ces terres boisees

Habitat Association Patterns of Forest and Steppe Birds of Northern Patagonia, Argentina

Abstract: I censused birds across a moisture gradient in northern Patagonia, Argentina, in the vicinity of Bariloche. Over a 60-km distance, the 12 sites ranged from grassland at lower elevations to upland climax Nothofagus forests of the eastern Andes. Here, I correlated bird abundance and diversities with various vegetation measures. Using all sites, bird diversities and abundances were positively correlated with various foliage measures. When grasslands were excluded, however, an inverse relationship was found: birds were more diverse and abundant in the lower stature shrub communities than in complex forests. Multiple regression analyses of this apparently paradoxical situation indicated that certain species of plants probably had important effects on community structure.

Shiny Cowbird Parasitism in Two Avian Communities in Puerto Rico

Abstract: Molothrus bonariensis parasite 42% des nids d'especes residentes (rapaces exclus) a Porto Rico. Les consequences en sont: diminution du succes reproducteur et de la productivite de l'hote

Song Repertoire Size and Male Quality in Song Sparrows

Abstract: Il n'a pas ete trouve de relation entre l'importance du repertoire et les divers parametres de qualite du mâle chez Melospiza melodia

Preferred Nest Spacing of an Obligate Cavity-Nesting Bird, the Tree Swallow

Abstract: In order to determine the preferred dispersion of a population of breeding Tree Swallows (Tachycineta bicolor) in Ontario, we set up an abundant supply of nest boxes with a variety of distances between them. The 72 boxes were arranged in 12 equidistantly spaced spirals. Within a spiral, the distance between boxes was much smaller than between spirals. Over five breeding seasons, we observed the order and positions in which swallows settled in the spirals. Pairs of swallows usually settled in empty spirals before settling in spirals occupied by conspecifics, but they did not avoid nesting in spirals occupied by Eastern Bluebirds (Siulia sialis). Swallows did not show any spacing preferences when their nearest neighbors were in different spirals, and were therefore more than 36 m away. Within spirals, however, swallows nested as far as possible from each other when their nests were less than 14 days apart. Swallow nests in the same spiral also tended to be spaced out temporally. We conclude that, over the range of distances within a spiral, Tree Swallows prefer to space their nests as far from conspecifics as possible. The observed spacing pattern probably arises from territorial behavior that is directed toward defense of a nest site from intruders. Breeding birds disperse their nests in a variety of patterns ranging from the tightly clumped distribution of colonial species to the uniform distribution of territorial species (Lack 1968). The spatial distribution of resources such as food, nest sites, and nest materials; the intraspecific competition for these resources and for mates; and predation pressure are some of the factors determining the breeding dispersion of individuals (Crook 1965, Lack 1968, Hoogland and Sherman 1976). In this paper, we report on an experimental approach to determine the preferred nesting dispersion of a cavity-nesting species, the Tree Swallow (Tachycineta bicolor). Swallows (Hirundinidae) show varying degrees of gregariousness during the breeding season. Dispersion may depend upon a particular species’ nesting requirements. Some species build their own nests, while others use existing crevices in trees, rocks, and walls, or old burrows excavated by other animals. Those species that build their own nests have some choice in the nature of their association with conspecifics, and intraspecific interactions are probably the most important determinants of their dispersion patterns (e.g., Hoogland and Sherman 1976, Snapp 1976). For example, Cave Swallows (Hirundo @vu) and Cliff Swallows (H. pyrrhonota), which build globular nests of mud pellets, breed in dense colonies, as do Bank Swallows (Riparia riparia; Bent 1942) and White-backed Swallows (Cheramoeca leucosternum), which excavate their own burrows in sand banks (Serventy and Whittell 1976). On the other hand, another burrower, the Banded Sand Martin (Riparia cincta), nests solitarily (McLachlan and Liversidge 1965) and another mud-nest builder, the Barn Swallow (Hit-undo rustica), nests solitarily or in loose colonies (Snapp 1976). Those species that must nest in existing holes and cavities have distributions that are determined primarily by the availability of suitable nest sites (von Haartman 1957, Holroyd 1975). The Tree Swallow, Purple Martin (Progne subis ), and Northern Rough-winged Swallow (Stelgidopteryx serripennis) are examples of obligate cavity-nesting swallows. Cavity-nesting species show considerable intraspecific variation in their nesting behavior, and may nest either solitarily or colonially, depending on the distribution of nest sites (Bent 1942). Since spacing patterns are so diverse in cavitynesters, it is of interest to determine which, if any, nesting dispersion pattern is actually preferred. Nest spacing preferences of cavity-nesting species can be determined by providing many nest sites with different distances between them. Once the preferred spacing is known, one can begin to look for the behavioral mechanisms by which the spacing pattern is achieved, and for any effects of the spacing pattern on fitness.

Song Repertoires and Song Sharing by American Redstarts

Abstract: We studied the extent to which male American Redstarts (Setophaga ruticilla) share songs in their repertoires. Examining samples of songs from three locations in New Brunswick, Canada, we found significant heterogeneity in the frequencies of the different songs across the locations. The extent to which neighbors shared songs related to increasing repertoire size (mean 4.4 songs/adult male). In the relatively larger sample at St. Andrews, neighboring adult males shared significantly more song types (P < 0.05) than did adult males chosen at random. However, this result applied only to individuals with intermediate-sized repertoires (four songs). Subadult males at St. Andrews shared as much with neighboring adult males as did adult males among themselves. In the small, island population at Back Bay, adult males shared noticeably more songs than at St. Andrews. We attribute the difference in degree of song sharing to demographic aspects, including patterns of settlement, interacting with tendencies to copy songs. Therefore, any so-called "dialects" in songs of American Redstarts seem more as "epiphenomena" resulting from competiton between males rather than as indications of local adaptations of males. The geographic distribution of similar patterns of sound used in bird song is often considered to reflect one or a number of selective pressures. These include preference for males adapted to local environments and identified by particular song patterns (Baker 1975, Baker et al. 1981); the competitive interactions of males for gaining advantage either through mimicry of superiors (Payne 1981, 1982) or by improving their competitive status in direct aggressive encounters between males (Hinde 1958, Lemon 1968); and the effects of selection on acoustic features of the song by environmental factors (Richards 1981). Alternatively, distributions of bird songs may reflect only the effects of chance with no direct selection involved (Slater et al. 1980). Patterns of song similarity are known to vary considerably across species (Mundinger 1983), consequently a single functional basis for the distribution of bird songs need not apply. In this study, we examined the distribution of songs of American Redstarts (Setophaga ruticilla) resident in coastal New Brunswick. Although islands are common along the coast of New Brunswick, there appear to be no major boundaries to dispersal for this migratory species. Relative to other warblers (Parulidae), this species has moderate-sized repertoires averaging somewhat over four songs per male. We investigated: (1) whether song types were shared to a significant degree among three close sites; and (2) whether sharing was significantly greater between immediate neighbors on contiguous territories than between non-neighbors. In order to make these comparisons, we first established a classification of the songs and considered the problem of repertoire size on the extent of song sharing. Having made these comparisons, we then examine the results in light of the hypotheses cited above. Although this study in itself is not sufficient for the elimination of any of the hypotheses, nonetheless the results point to the use of the songs in competition between males (see Discussion). METHODS AND MATERIALS

Influence of high density and parental age on the habitat selection and reproduction of black-billed magpies

Abstract: On observe, sur deux ans, dans le nord de l'Utah les habitats preferentiels pour la reproduction d'une population dense de Pica pica hudsonia. Cet oiseau a un systeme territorial maleable en relation avec la densite de population et une forte densite ne limite pas par elle-meme leur productivite

Reproduction and survival of seabirds in Oregon during the 1982-1983 El Niño

Abstract: Etude portant sur Uria aalge, Phalacrocorax penicillatus, Phalacrocorax pelagicus et Cepphus columba

Vegetation and soils of burrowing owl nest sites in Conata Basin, South Dakota

Abstract: On caracterise la vegetation et les sols des Terriers abandonnes de Cynomys ludovicianus et utilises pour nidifier par Athene cunicularia et on les compare avec ceux des terriers non occupes par l'oiseau

Leucism in Eared Grebes in Western North America

Abstract: Leucism is the complete loss of a particular pigment, or all pigments, in feathers but not in soft-parts. It may be as slight as a single white feather or as pervasive as an all-white bird with normal eyes, bill, and legs (Buckley 1982). The condition has been documented, usually as a curiosity and under the term "albinism," in hundreds of species. Its incidence is said to differ greatly among species (e.g., Sage 1963, Gross 1965), but the data for that conclusion are unconvincing because a high percentage of reports pertain to species that associate with, or are hunted by, man. As a result, observational bias is potentially strong. For only a few species (e.g., storm-petrels; Baptista 1966) has it been possible to consider the phenomenon more broadly and to investigate the frequency of leucism in natural populations of birds. The subject is interesting because leucism, like any variable condition, may provide indirect evidence of underlying genetic variability. Furthermore, if its frequency can be measured, this may allow some inferences to be drawn about the strength of selection against abnormally-colored individuals. In this paper, I present data on leucism compiled incidental to other research during a four-year (1981-1984) study of Eared Grebe (Podiceps nigricollis) biology at Mono Lake, California. Other aspects of this research have been presented elsewhere (Mahoney and Jehl 1985; Storer and Jehl, in press).

Nest-Site Selection by Sage Sparrows

Abstract: --In 1980, 1981, and 1982, we studied nest-site selection by Sage Sparrows (Amphispiza belli) in a sagebrush community in Idaho to provide a thorough description of nest-site characteristics and preferences. Sage Sparrows nested in areas where sagebrush coverage was sparse but shrubs were clumped. All nests were situated in big sagebrush (Artemisia tridentata) plants; large, living shrubs were strongly preferred. Nest placement relative to the ground and shrub perimeter seemed quite specific. Sage Sparrows avoided positioning nests on the southwest side of shrubs. The Sage Sparrow (Amphispiza belh) is a common species breeding throughout much of the Great Basin region of the western U.S. (Wiens and Rotenberry 1981). Some investigators have considered Sage Sparrows to be sagebrush (Artemisia spp.) obligates (Braun et al. 1976), although Hill (1980) and Green (1981) recorded them nesting in low densities in fields with little or no sagebrush. Rich (1980) and Reynolds (1981) reported limited information on Sage Sparrow nest placement, but some questions were not addressed: Do Sage Sparrows show preferences in the nest sites they choose as well as in the manner in which they position their nests within the nesting substrate? Are habitat characteristics in the immediate vicinities of nests important in Sage Sparrow nestsite selection? Our objective was to comprehensively measure nest-site selection by Sage Sparrows occupying a sagebrush community in order to provide a more complete description of nest-site characteristics of this species and to identify nest-site preferences. Because Sage Sparrows are closely associated with sagebrush habitat and because sagebrush rangeland often is altered (Braun et al. 1976), thorough documentation of Sage Sparrow nesting habitat requirements is needed. STUDY AREA AND METHODS

Winter mortality in common barn-owls and its effect on population density and reproduction

Abstract: Etude menee dans le nord des l'Utah. Une assez importante mortalite hivernale s'observe dans cette region pour Tyto alba. La cause apparente de mort est le jeune alimentaire. On observe egalement un declin de la taille de couvee et du succes reproducteur

Mate retention in Caspian Terns

Abstract: Observation de colonies des Sterna caspia au nord-est du lac Michigan: des facteurs autres que le succes reproducteur anterieur influencent le choix du partenaire et la fidelite vis-a-vis de lui

Adaptations of Migratory Shorebirds to Highly Saline and Alkaline Lakes: Wilson’s Phalarope and American Avocet

Abstract: Wilson’s Phalaropes (Phalaropus tricolor) and American Avocets (Recurvirostra americana) occur in large numbers at hypersaline and alkaline lakes. Comparing birds from three lakes of different salinity and alkalinity in the Great Basin of western North America, we found no evidence of salt-loading: blood hematocrit, pH, osmolality, and sodium concentration were not elevated; stomach osmolality and sodium concentration were only slightly higher than the body fluids of the birds’ hypo-osmotic prey (brine shrimp and brine flies); salt glands were not enlarged and averaged a relatively low percentage of body weight (0.02%). Through a combination of behavioral and anatomical adaptations, phalaropes and avocets evidently are able to rid their prey of most adherent lake water and thereby largely avoid the problems of salt-loading and the ingestion of harmful ions. Both species occupy hypersaline habitats for long periods and probably derive most of their water needs from the body fluids of their prey. Their use of fresh water is sporadic and may not be required for osmoregulatory balance. Alkaline and hypersaline lakes, despite being harsh physical environments, are prime habitats for a few species of resident (e.g., flamingos) and a somewhat larger number of migratory waterbirds. Mono Lake, California, a large hypersaline (2’ 12 x the concentration of sea water) and alkaline (pH x 10) lake at the eastern base of the Sierra Nevada, attracts large numbers of a few of these species each year. Approximately 45,000 California Gulls (Larus californicus) nest there; in summer and in fall, tens of thousands of Wilson’s (Phalaropus tricolor) and Red-necked (P. lobatus) phalaropes stop over on their southward migration (Jehl 198 l), and hundreds of thousands of Eared Grebes (Podiceps nigricollis) stage there (Storer and Jehl 1985). American Avocets (Recurvirostra americana) are also common at hypersaline lakes, although at Mono Lake only a few pairs breed and flocks of several hundred occur in autumn. Hypersaline lakes are attractive to these birds because they typically lack fish, which allows the few invertebrates that can occupy them to attain great abundances. These, in turn, serve as food for the birds. At Mono Lake, brine shrimp (Artemia sp.) and brine flies (Ephydru hians) become super-abundant at some seasons. Birds feeding on these invertebrates, either by pecking them from the surface of the water or by catching them while driving, might be expected to ingest large amounts of lake water and thereby incur deleterious salt loads. Yet, our previous studies of California Gulls (Mahoney and Jehl 1985a) and Eared Grebes (Mahoney and Jehl 1985b) at Mono Lake, where salinities have varied from 72 to 90 ppt (2,160-2,700 mOsm/kg) in 1982-l 984, have shown that this is not the case. These species seem to have no special anatomical or physiological adaptations for dealing with high salt loads. Instead, they largely avoid osmoregulatory problems behaviorally, by ridding their food of adherent lake water before swallowing it. Gulls and grebes differ markedly in their use of fresh water. Gulls visit freshwater streams to drink and bathe several times each day, whereas grebes, although they may remain continuously at Mono Lake for as long as six months (Jehl, unpubl. data), never visit fresh water. Wilson’s Phalaropes and American Avocets (Fig. 1) have intermediate patterns of water use; both visit fresh water regularly, though probably not daily. If phalaropes and avocets ingest large quantities of Mono Lake water and its attendant osmotic and ionic load, they could be expected to show changes in blood chemistry, hydration state, and salt gland size. In order to determine how great a salt load these birds incur while feeding at the lake, we made the following measurements: blood pH and hematocrit; serum osmolality, sodium, and potassium; composition and osmolality of stomach contents, prey body fluids, and lake water; body water content; and salt gland weights. We then compared these values from Mono Lake birds to those

Experiments on Olfactory Detection of Food Caches by Black-Billed Magpies

Abstract: Etude experimentale Pica pica pour redecouvrir des cachettes alimentaires utilise des reperes multiples qui peuvent inclure la memoire et des reperes olfactifs et visuels. Les reperes olfactifs lui sont particulierement utiles pour trouver les aliments caches par des conspecifiques

Territoriality and interspecific aggression in Steamer-ducks

Abstract: indicates that Burrowing Owls modify prairie dog burrows used as nest sites. Presumably, sandy soil would facilitate enlarging burrow passageways. Coulombe (1971) stated that in California burrow diameters averaged 20 cm, and suggested that owls may modify burrows that have been abandoned by rodents. In addition, sandy soils drain rapidly, which would reduce nest flooding during frequent spring and summer rainstorms.