Showing papers in "The Condor in 1986"

Culture and the evolutionary process

Abstract: How do biological, psychological, sociological, and cultural factors combine to change societies over the long run? Boyd and Richerson explore how genetic and cultural factors interact, under the influence of evolutionary forces, to produce the diversity we see in human cultures. Using methods developed by population biologists, they propose a theory of cultural evolution that is an original and fair-minded alternative to the sociobiology debate.

The Florida scrub jay : demography of a cooperative-breeding bird

Abstract: Florida Scrub Jays are an excellent example of a cooperative-breeding species, in which adult birds often help raise offspring not their own. For more than a decade Glen E. Woolfenden and John W. Fitzpatrick studied a marked population of these birds in an attempt to establish a demographic base for understanding the phenomenon of "helping at the nest." By studying both population biology and behavior, the authors found that habitat restraints, rather than kin selection, are the main source of the behavior of Florida Scrub Jays: the goal of increasing the number of close relatives other than descendants in future generations is of relatively minor importance in their cooperative-breeding behavior. The Florida Scrub Jay lives only in the Florida oak scrub. All acceptable habitat is constantly filled with breeders. Each year about half of the pairs are assisted by one to several nonbreeding helpers. This book provides extensive data on fecundity, survivorship, relatedness, and dispersal to establish the demographic milieu and to address questions arising out of observed helping behavior--whom, how, when, and why the helpers help.

Seabird interactions with dolphins and tuna in the eastern tropical pacific

Abstract: Bird flocks associated with dolphins in the eastern tropical Pacific are described from observations obtained during eight cruises that took place from January to March of 1976, 1977, 1979, and 1980. In the northern tropical waters between latitudes 5"N and 30"N, 43% to 53% of bird flocks co-occurred with dolphins. In equatorial and southern subtropical waters between latitudes SON to 12"s and in the central Pacific less than 8% of the flocks were associated with dolphins. In northern tropical waters about 70% of dolphin schools associated with flocks were composed of spotted or spotted plus spinner dolphins; conversely, 59% of spotted dolphin and 96% of spotted plus spinner dolphin schools co-occurred with bird flocks. Most large schools of these dolphins were associated with birds, and thenumber and diversity of bird species increased with dolphin school size. The average species composition of birds in dolphin-associated flocks of northern tropical waters was: boobies 4 I.%, Wedge-tailed Shearwaters (Puffinus pacificus) 3 1.4%, jaegers 12.8%, Sooty Terns (Sterna firscata) 6%, frigatebirds 3.6%, and others 4.5%. Positive statistical associations were found among these bird species, which are explained by common attraction to food made available by feeding yellowfin tuna. In the southern latitudes and in the central Pacific, flocks were dominated by Sooty Terns, and few flocks were associated with dolphins. These flocks appeared to be associated with skipjack rather than yellowfin tuna.

Scavenging Efficiency of Turkey Vultures in Tropical Forest

Abstract: L'efficacite depend du temps mis par l'oiseau pour detecter les carcasses en milieu couvert

Site Fidelity and Habitat Quality as Determinants of Settlement Pattern in Male Painted Buntings

Abstract: The spatial distribution of high and low quality Painted Bunting (Passerina ciris) territories on St. Catherines Island, Georgia, was determined through an examination of the distribution of food resources and polygynous pairings in 1976 and 1977. Based on the distribution of high and low quality territories, we predicted the pattern of territory settlement by males at the start of the breeding season. As predicted, males settled significantly earlier on high quality than on low quality territories in 1978 and 1979. However, not all males that initially acquired high quality territories were able to maintain them long enough to breed on them. Most of these males, which were subsequently displaced by returning site-faithful males, were settling for the first time on the study area, although some were returning males that had held low quality territories the previous year. New breeders and some returners initially settled in a pattern consistent with predictions based on territory quality; most returning males settled on the basis of site fidelity. Thus, the final settlement pattern was the result of an interaction between preference for areas of high quality and the return and site faithfulness of previous territory holders. The implications of this pattern of territory acquisition for the evolution of delayed maturation in males are discussed.

The Parasitic Behavior of the Bronzed Cowbird in South Texas

Abstract: Aspects of the breeding ecology of the Bronzed Cowbird (Molothrus aeneus) were studied from early April to mid-July or August 1980 to 1982 at the Santa Ana National Wildlife Refuge in southern Texas. Female Bronzed Cowbirds, similar to Brown-headed (M. ater) and Shiny (M. bonariensis) cowbirds, are generalists in their egg laying. Of five common host species on the refuge, all were equally and usually repeatedly parasitized. Of these, only the Green Jay (Cyanocorax yncas) and Longbilled Thrasher (Toxostoma longirostre) are larger than the cowbirds in body size and are better host choices based on their relative success as fosterers. Experimental parasitism of Couch's Kingbirds (Tyrannus melancholicus), Curve-billed Thrashers (Toxostoma curvirostre), and Great-tailed Grackles (Quiscalus mexicanus) showed that they eject cowbird eggs from the nest. Female Bronzed Cowbirds, like Shiny Cowbirds, pierce both host eggs and previously laid cowbird eggs. Approximately twice as many host eggs were pierced compared to cowbird eggs. In some parasitized nests, more than one cowbird laid eggs and final host clutch size was greatly reduced. The vocal reaction of host species to cowbird intrusion probably provided clues on nest location to nest-searching female cowbirds who were drawn to such stimuli. Like the other four parasitic cowbird species, Bronzed Cowbird nestlings possess no apparent special adaptation for brood parasitism. Their vocal nature, however, appears to give them a competitive edge against less vocal host nestmates.

Genetic Relationships of North American Cardueline Finches

Abstract: Starch gel electrophoresis was used to examine variation at 33 genetic loci in 19 taxa (15 species in 6 genera) of cardueline finches (family Fringillidae). Levels of heterozygosity and genetic distances were comparable to those reported from surveys of other avian taxa. Twentythree loci (70%) were polymorphic within taxa and/or were fixed at alternative alleles among taxa. Rogers’ genetic distances were used to construct phenograms, distance Wagner trees, and F-M trees; these provided hypotheses for the evolutionary relationships of taxa. The genetic data indicate that: (1) Coccothraustes, Pinicola, Leucosticte, Carpodacus, Carduelis, and Loxia are distinctive genera that vary in estimated age (as measured from nearest branch point) from approximately 14 MY (Coccothraustes) to 5 MY (Loxia); (2) species treated by the AOU (1983) as congeners within Carpodacus, Carduelis, and Loxia are correctly classified to genus; (3) the subgenera Acanthis, Astragalinus. Spinus, and Carduelis, within the genus Carduelis, are recognizable; (4) the crossbills (Loxia) are most closely allied to Carduelis among the genera examined; (5) Carpodacus purpureus and C. cassinii are closely related sister species whereas C. mexicanus is very distinct; (6) Loxia curvirostra and L. Zeucoptera re moderately different electrophoretically; (7) in contrast, the redpolls, Carduelisflammea and C. hornemanni exilipes, are similar genetically; (8) most speciation events in North American carduelines range from mid-late Pliocene (4 MY) to mid-Pleistocene (500,000 years) in age; but (9) subspecies diverged in the late Pleistocene. A phylogeny ofcardueline genera derived from these electrophoretic data agrees in major respects with one proposed by Raikow on the basis of hindlimb myology. The sequence of appearance of older taxa is still not resolved with certainty, however, because ofpartially conflicting molecular and morphologic results.

Breeding Biology of the Rhinoceros Auklet in Washington

Abstract: During 1974 through 1983, we investigated the breeding biology of the Rhinoceros Auklet (Cerorhinca monocerata) at three main colony sites on the coast of Washington: Destruction Island (offshore) and Protection and Smith islands (inland islands of the Strait of Juan de Fuca). Average burrow densities were higher offshore, where the auklets nested on shrub-covered slopes; inland auklets nested on grassy slopes and level areas. Egg-laying patterns varied among years and populations, although initiation dates on all islands were similar. The incubation periods averaged 45 days and ranged from 39 to 52 days. Chicks were brooded, on average, for 3.9 days (range zero to 9 days). On Protection Island, early-hatched young grew more rapidly than chicks hatched at a later date. Chicks on offshore islands were fed a variety of fish, whereas those on inland islands were fed primarily two species. The inland chicks were fed heavier fish loads, reached heavier peak body weights, and were heavier when they fledged than were offshore chicks. Breeding success was higher on the inland colony sites.

Variation in the composition of the eggs and chicks of american coots

Abstract: I evaluated the composition of 97 fresh eggs and 43 one-day-old chicks of the American Coot (Fulica americana) to determine if the constituents of eggs or chicks show allometry. Heavier eggs contained proportionately less albumen but proportionately more yolk, and consequently had a higher energy density than lighter eggs. Albumen weight varied more among than within clutches, presumably due to variation in the qualities of coot territories during nesting. Within clutches, the lipid content of eggs declined with laying sequence, but albumen weights remained constant. Moreover, newly hatched chicks contained proportionately more lean dry material if they hatched from large eggs than if they hatched from small ones. These patterns of variation appear to increase the disparities in size of these asynchronously hatching young, and thus result in differential survival probabilities among siblings.

Energetics of growth in nestling savannah sparrows: a comparison of doubly labeled water and laboratory estimates

Abstract: The energy expenditure of free-living nestlings has previously been estimated by any of several methods, each of which contains assumptions that may result in errors of uncertain magnitude. We evaluated the energy budget of nestling Savannah Sparrows (Passerculus sandwichensis) by analyzing their oxygen consumption and their accumulation of energy in tissues during growth. These results were compared with those obtained by means of the doubly labeled water (DLW) technique. From data on oxygen consumption of individual nestlings in metabolism chambers at 35*C, we calculated that a neonate metabolized 110.4 kJ of energy during the eight days that it occupied a nest. Applying standard conversion factors, we determined that a nestling accumulated 20.0 and 61.6 kJ of energy in lipid and non-lipid dry matter, respectively, for a total production (P) of 81.6 kJ. Direct evaluation of the energy in tissues by means of bomb calorimetry indicated that nestlings actually accumulated 75.2 kJ of energy, a value 7.8% lower than we previously obtained by converting lipid and non-lipid dry matter to energy with accepted conversion factors. From our analysis using data obtained in the laboratory, total metabolized energy (TME) equaled 185.8 kJ. Field metabolism, as estimated by DLW, summed to 171.5 kJ for the 8-day nestling period whereas estimates from oxygen consumption in the laboratory amounted to 110.4 kJ, a 35.6% difference. This disparity may have resulted from an increased energy expenditure for thermoregulation and activity during the latter stages of the nestling period, components which are not measured in laboratory experiments. Total metabolized energy (TME) as estimated by DLW (246.7 kJ) differed from laboratory estimates (182.9 kJ) by about 25%. Production (P) to TME ratios for Savannah Sparrows on a daily basis were nearly as high as those for altricial embryos (Agapornis) with values declining from a maxima of 0.4-0.5 to 0.1 near the end of the nestling period.

Determinants of Guild Structure in Forest Bird Communities: An Intercontinental Comparison

Abstract: We examined the patterns of food resource utilization (guild structure) of 41 species of birds that breed in eucalypt forests and woodlands in south temperate Australia, and compared them to the results of a similar study in a north temperate, broad-leaved forest in North America (Holmes et al. 1979). Both studies used the same field methods and analytical techniques. The Australian community was more complex as inferred from the greater number of guilds (9 vs. 4) and from the results of principal components and factor analyses of the foraging data. These multivariate methods showed that guilds at the Australian site were separated first by differences in foraging height and bird weight, and second by foraging methods and food substrates. Use of specific foraging substrates (e.g., exfoliating bark) and food resources (e.g., nectar and other carbohydrates) were important at finer scales of separation. The results support the hypothesis that vegetation structure and food availability, which vary with plant species and vertical strata, produce particular sets of foraging opportunities for birds. These in turn influence which species can obtain food successfully, and thus can be considered primary determinants of guild structure. This comparison of food utilization patterns of birds in contrasting habitats provides insight into the factors determining bird community organization.

Growth and Development of Canada Goose Goslings

Abstract: Under natural conditions goslings of Cackling Canada Geese (Branta canadensis minima) grew more rapidly (k = 0.074, Gompertz equation) than ducks but at a rate similar to other arctic nesting geese. Lipid levels in 2-day-old goslings were sufficient to meet energy requirements for less than one additional day. The liver, legs, and components of the gastrointestinal tract in Cackling Geese were relatively larger at hatching than in altricial birds. These tissues completed growth about three weeks before fledging as compared to one week in similar sized altricial birds. Early growth of digestive organs is probably related to the herbaceous diet of geese. Comparison of growth patterns of gallinaceous birds with those of geese superficially supports Ricklefs’ hypothesis that proportion of mature tissue at hatching regulates growth rates. Examination of growth within the Anatidae, however, suggests that temporal patterns in food quality and availability may have been important influences in the evolution of growth patterns in these species.

Blood Constituents and Their Relation to Diet in Urban and Rural House Sparrows

Abstract: To determine whether habitat-related differences in diets of House Sparrows (Passer domesticus) were reflected in their blood, we measured hematocrits and plasma concentrations of cholesterol, albumin, uric acid, and blood urea nitrogen (BUN) of sparrows from urban and rural habitats in Centre County, Pennsylvania, during the breeding season. We also determined the protein and fat content of food samples recovered from sacrificed birds. Significantly elevated plasma cholesterol and BUN levels in House Sparrows from the urban area reflected the higher fat and protein content of the urban diet. Albumin and uric acid levels were also higher in urban than in rural birds, but not significantly so. Blood values were further influenced by age, sex, and date of collection. The analysis of blood may be useful in assessing the quality of diets eaten by wild birds.

Lack of Effects from Sampling Blood from Small Birds

Abstract: In Peru, we thank E. Ortiz for his assistance in the field, PESCA PERU for its hospitality, and W. Brown, C. Hays, M. Plenge, B. Torres, and P. Yengle for logistic and moral support. In Galapagos, we thank the personnel and scientists of Beagle IV, National Park Service, and Darwin Station for assistance. We owe special thanks to H. Hoogstraal who identified the ticks, provided essential references, and generally fostered our interest and knowledge. We thank The International Council for Bird Preservation, National Science Foundation (DEB77-16077), Organization of American States, Smithsonian Institution, World Wildlife Fund, and Princeton University for financial support. The FitzPatrick Institute supported data analysis and the preparation of the paper. This is contribution number 374 of the Charles Darwin Foundation.

Composition of blue-winged teal eggs in relation to egg size, clutch size, and the timing of laying

Abstract: Blue-winged Teal (Anas discors) eggs from 172 nests were analyzed to determine how organic composition was affected by clutch size, laying sequence, nest attempt, laying date, and egg size. On average, eggs weighed 28.1 g and were 46% yolk and 44% albumen. Eggs contained 3.6 g lipid and 3.2 g protein almost equally distributed between yolk and albumen. Yolk increased a disproportionate amount and the proportion of albumen tended to decrease with increased egg mass. Consequently, large eggs contained proportionately more lipid than small eggs. Shell decreased in proportion with increasing egg mass. For most egg traits 60 to 80% of the variation occurred between clutches rather than within clutches. Teal eggs did not vary in composition in relation to clutch size, laying sequence, nest attempt, or the timing of laying on either a seasonal or yearly basis. Eggs in renests weighed 0.8 g less than eggs from the first clutch of the same females; however, this disparity was not reflected in differences in lipid or lean dry mass for the collected eggs of known renesters.

Sunrise, skylight polarization, and the early morning orientation of night-migrating warblers

Abstract: Field observations reveal that night-migrating passerines sometimes fly during early morning hours. Functional consideration of daytime flights have overshadowed proximate questions regarding the sensory basis of daytime orientation. I conducted a series of early morning cage-orientation experiments in spring with four species of migrating warblers (Parulinae) on the north coast of the Gulf of Mexico. Whereas birds were poorly oriented on overcast mornings, the headings for three species were oriented in a seasonally appropriate direction when individuals were tested on clear mornings with the horizon glow from the rising sun visible. Moreover, the direction of activity was influenced in a predictable way by manipulating the pattern of skylight polarization. Skylight at sunrise appears to function as a source of directional information for morning flights of migrating warblers. This interpretation is consistent with field observations of the orientation behavior of free-flying migrants, and reinforces speculation that solar-related information is involved in the orientation of ongoing migratory flight, or redetermined orientation following nighttime displacements. In any case, the responsiveness of several species in a cage situation may allow controlled experiments on the question of course correction and redetermined

A Field Test of the Variable Circular-Plot Censusing Method in a Sierran Subalpine Forest Habitat

Abstract: The density and distribution of territories were determined for 21 species in a 48-ha Sierran subalpine forest study plot by an intensive program of spot-mapping and nest monitoring. About 10% of the total breeding individuals were color-banded and about 75% of the nests of all species were found. Variable circular-plot (VCP) censuses were simultaneously conducted in the same study plot. The VCP method, with minimum effort (48 stations), could describe community parameters reasonably well and could distinguish common from rare species, but could not correctly determine the relative abundances of the common species, could not correctly describe the distribution of territories within the study plot, and produced errors in density estimates for the common species that ranged from 57% to + 65%. When the effort was increased threefold (144 stations), the accuracy of the method was improved so that it produced more or less acceptable relative abundances for even the common species and was marginally capable of describing the distribution of territories for 37% of the species, particularly for those species whose distributions were markedly non-uniform, but it still produced errors in density estimates for the common species that ranged from -67% to +96%. Interestingly, VCP total count often performed nearly as well as the calculated VCP density in determining relative abundances. The accuracy of the VCP method may be expected to be poor for species with low population densities, large territory sizes, high mobilities, and ventriloqual vocalizations, and for habitats that are dense and highly three-dimensional.

Sooty Shearwaters off California: Distribution, Abundance and Habitat Use

Abstract: Sooty Shearwaters (Puffinus griseus) migrate to waters of the North Pacific Ocean each spring after nesting on colonies in the South Pacific. Their numbers and habitat affinities off California were investigated during 60 aerial and 24 ship surveys in 1975 to 1978 and 1980 to 1983. Population densities computed monthly indicated arrival throughout California waters in late March and departure of most birds from southern California one to two months earlier than in waters to the north. Peak densities exceeded 10 birds km-2 over the shelf and upper continental slope off central California for two to six months each year but reached these levels on only a few occasions in northern and southern California. Densities in all areas generally were highest in late spring and reached secondary peaks in midto late summer after variable declines from the spring peak. Populations are estimated to total 2.2 to 4.2 million birds in May, June, or July, depending on year and method of calculation. Population turnover may be rapid; total numbers of birds migrating through the area may be much higher than the "instantaneous" population. Shearwaters concentrated in relatively shallow, cool waters, especially where strong thermal gradients marked the edges of upwellings.

The Relationship of Energetics of Falconiform Birds to Body Mass and Climate

Abstract: I measured body temperature and resting metabolic rate as a function of ambient temperature in eleven species of falconiforms. Body temperatures range from 37.1?C to 41.3?C and are independent of body size and climate. Resting metabolic rates correlate with variations in body size and climate. Falconiforms from hot habitats have lower resting metabolic rates than those from temperate habitats. The relationship between the mass-specific metabolic rate (mW g-') and mass (g) for birds in this order may be expressed as IHm = 34.62W-o'36. The relationship between the minimal thermal conductance (mW (g*C)-') and mass (g) for falconiforms may be expressed as C = 2.96W-0.45

Nesting Losses and Nest Site Preferences in House Wrens

Abstract: This study examined nest sites selection by a cavity nesting species, the House Wren (Troglodytes aedon), at two sites in Ontario, Canada. Descriptive information suggests that predation is the most important factor reducing House Wren reproductive success. Nests built in sparse vegetation suffered less predation than those in dense vegetation. Descriptive and experimental data demonstrated that House Wrens exhibit strong preference for nesting boxes in sparse vegetation, presumably because here they are more successful. We suggest that the greater success of House Wrens in sparse vegetation results from their more effective nest defense against other conspecifics that may attack wren nests. We predict that the ability of males to defend suitable nest sites influences their mating success.

The singing behavior of female northern cardinals

Abstract: Observations were made and playback experiments were performed in central Kentucky in an attempt to determine the function(s) of singing by female Northern Cardinals (Cardinalis cardinalis). Singing by female cardinals was uncommon and was noted primarily during the period after males had established territories and before nesting had begun (early March to mid-May). When singing, females were generally joined by singing mates. Experiments revealed that females rarely sang in response to playback of male or female songs. Such evidence suggests that singing by female Northern Cardinals is important in pair bonding and, perhaps, in reproductive synchronization.

Hematocrits and Erythrocyte Numbers for Cooper's and Sharp-Shinned Hawks

Abstract: Hematocrits and RBC counts have been used to evaluate the "health" of the oxygen transport system in raptors. Few values ofhematocrit and erythrocyte (RBC) numbers have been reported for North American accipiters. Values for Northern Goshawks (Accipiter gentilis) and Cooper's Hawks (A. cooperii) were reported by Elliott et al. (1974) and by Hunter and Powers (1980). Our objective was to provide a larger database of hematocrit values and RBC counts for healthy wild accipiters. The scant information on hematocrit and RBC counts of raptors is mostly from captive, relatively inactive birds at low altitudes. In contrast, the migrating accipiters in this study had been actively flying, probably for several hours each day at relatively high altitudes, prior to being captured. Indirect evidence suggest that healthy, migrating raptors may have significantly different hematocrits and RBC counts than healthy captives. For example, it is well known that living at high altitudes stimulates increased production of RBCs. Secondly, acute dehydration can increase the RBC count without a concomitant increase of red-cell mass; Hart and Berger (1972) speculated from experimental investigations of three avian species (non-raptors) that dehydration occurs in migrating birds.

Survival and reproduction of dispersing blue grouse

Abstract: Dispersal in a declining population of Blue Grouse (Dendragapus obscurus) was studied over four years on Hardwicke Island, British Columbia, Canada, by radio-tracking 66 individuals and reobserving or recapturing 126 banded individuals. On a 464-ha main study area, numbers of territorial males decreased from 152 to 94, breeding females from 276 to 113, and young grouse alive in late summer from 847 to 224 during the period of study. Despite this, dispersal distances did not vary between years and bore no clear relationship with adult densities in spring or density of juveniles in the previous fall. Rates of survival and reproduction for longdispersers (grouse moving greater than the median dispersal distance) and short dispersers (grouse moving less than the median dispersal distance) were similar. Similar results were noted for grouse that left the study area (dispersers) and those that remained on the study area (non-dispersers). Overall, there was little evidence that dispersers fared poorly or that dispersal was greatly influenced by population density.

The Effect of Photoperiod and Temperature on Testicular Growth in Captive Black-Billed Magpies

Abstract: The gradual increase in daylength each winter and spring in the Northern Hemisphere has been established as the primary proximate stimulus for reproduction in numerous north-temperate bird species. Photoperiodic induction of the secretion of gonadotrophins in advance of the breeding season, which in turn causes increased gonadal hormone secretion and gametogenesis, ensures that a bird will be physiologically and behaviorally prepared for reproduction when food and weather conditions become favorable (see reviews by Mutton and Westwood 1977, Famer and Gwinner 1980, Wingfield and Farner 1980). Variation in the timing of breeding can often be correlated with annual variation in the vernal increase in ambient temperature (e.g., Lack 1950, Goodacre and Lack 1959, Slagsvold 1976, Wingfield et al. 1983). The delayed breeding commonly observed in years with periods of cold spring weather may be the result of a decreased rate of accumulation of the nutrients and energy necessary for egg formation by females, owing to increased thermoregulatory demands and scarcer food during cold weather (Perrins 1970, O’Conner 1978, Dhondt and Eyckerman 1979). The delay may also be a result of a modifying effect of temperature on the neuro-endocrine control system of either or both males and females. Modification of photoperiodic responses by temperature presumably could synchronize the annual reproductive effort with environmental conditions that maximize the probability of success. This modifying effect has been most thoroughly studied in Gambel’s White-crowned Sparrows (Zonotrichia leucophrys gambeliz). Famer and Mewaldt (1952) Famer and Wilson (1957), and Lewis and Famer (1973) demonstrated that low temperatures exert a slight inhibitory effect on testicular development in this subspecies when birds were maintained on LD 15:9 or LD 18:6. Additionally, plasma levels of luteinizing hormone, testosterone, and dihydrotestosterone did not change significantly when birds maintained at LD 20:4 and 23°C were exposed to 5°C for four days (Wingfield et al. 1982). The slight effect that temperature has on testicular growth in a relatively long-range migrant such as Z. 1. gambelii is not surprising. Modification of testicular development by temperature would not appear to be adaptive for a migratory species, because temperatures encountered at the wintering ground and during migration (during the initial stages of testicular growth) are of little value as