bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relationships among Territory Size, Habitat, Song, and Nesting Success of Northern Cardinals
Authors: Conner Richard N. , Anderson Mary E. , Dickson James G. 
Published: October 2019

Abstract
We collected data from 30 territories of Northern Cardinals (Cardinalis cardinalis) during 3 breeding seasons (1979-1981) in eastern Texas. Territory size was positively correlated with tree height and negatively correlated with the density of foliage at ground level and at 3 m above the ground, and with the density of shrubs. Nesting success was positively correlated with presence of patchy understory foliage and arthropod biomass in territories. Cardinals with low song complexity and shorter songs held better-quality territories and had better nesting success than cardinals with more complex songs. We suspect that young males may use long, complex songs to establish a territory initially, and in subsequent years put less time and effort into song and more into care and defense of young.
Brood Parasitism in a Host Generalist, the Shiny Cowbird: I. The Quality of Different Species as Hosts
Authors: Mason Paul 
Published: October 2019

Abstract
The Shiny Cowbird (Molothrus bonariensis) of South America, Panama, and the West Indies is an obligate brood parasite known to have used 176 species of birds as hosts. This study documents wide variability in the quality of real and potential hosts in terms of response to eggs, nestling diet, and nest survivorship. The eggs of the parasite are either spotted or immaculate in eastern Argentina and neighboring parts of Uruguay and Brazil. Most species accept both morphs of cowbird eggs, two reject both morphs, and one (Chalk-browed Mockinbird, Mimus saturninus) rejects immaculate eggs but accepts spotted ones. No species, via its rejection behavior, protects the Shiny Cowbird from competition with a potential competitor, the sympatric Screaming Cowbird (M. rufoaxillaris). Cross-fostering experiments and natural-history observations indicate that nestling cowbirds require a diet composed of animal protein. Because most passerines provide their nestlings with such food, host selection is little restricted by diet. Species-specific nest survivorship, adjusted to appropriate values of Shiny Cowbird life-history variables, varied by over an order of magnitude. Shiny Cowbirds peck host eggs. This density-dependent source of mortality lowers the survivorship of nests of preferred hosts and creates natural selection for greater generalization. Host quality is sensitive to the natural-history attributes of each host species and to the behavior of cowbirds at nests.
Influence of Resource Abundance on Use of Tree-Fall Gaps by Birds in an Isolated Woodlot
Authors: Blake John G. , Hoppes William G. 
Published: October 2019

Abstract
The occurrence of birds in forest understory and tree-fall gaps during spring and fall migration periods was determined in an isolated woodlot. We used mist-net captures to test the hypothesis that birds are attracted to gaps because of higher resource levels. We captured 1,010 birds (74 species) in spring and 458 (44 species) in fall. Total captures and captures per net were higher (P < 0.001) in gaps during spring and fall. Mean number of species per net was higher in gaps (P < 0.001) during both seasons, but total species in gaps (69 spring, 43 fall) was not significantly higher than in forest understory (60 spring, 28 fall). Of 44 species represented by adequate sample sizes (n > 5) in spring, 9 were significantly (P < 0.05) more common in gaps and 2 were more common in forest understory. Nine of 17 species were captured more often (P < 0.05) in gaps during fall. During spring, flycatchers, ground insectivores, foliage insectivores, and granivore-omnivores were captured more frequently (P < 0.05) in gaps. Flycatchers showed no difference in fall, but other trophic groups, including frugivores, were captured more frequently (P < 0.05) in gaps than in forest understory sites. Bark foragers showed no statistical preference for gaps or forest understory in spring or fall. Total species per net and total captures per net correlated positively (P < 0.05) with density of foliage in the lower canopy and negatively with density of upper canopy foliage in both spring and fall. Total species and captures correlated positively (P < 0.05) with insect abundance in spring and with fruit abundance in fall. Foliage insectivores correlated positively with low canopy foliage and insect abundance in both spring and fall. Captures of frugivores correlated with fruit abundance in fall. These data support the hypothesis that birds are attracted to tree-fall gaps because of higher resource abundance and provide further evidence of the importance of habitat heterogeneity to the structure and composition of bird communities.
Egg Formation in Cassin's Auklet
Authors: Astheimer Lee B. 
Published: October 2019

Abstract
Female Cassin's Auklets (Ptychoramphus aleuticus) were given oral doses of lipophilic and proteophilic dyes during their prelaying period. Yolk ring structure in freshly laid eggs was analyzed to determine the timing of yolk deposition using the dye-stained layer as a date marker within the yolk. Additional information from necropsies of five females killed at specific intervals during the formation of a replacement egg indicated that only a single follicle enlarges in the ovary during a reproductive event and this yolk requires about 8 days to complete rapid yolk deposition (RYD). Once RYD is completed, the egg is not laid for a period of 4.2 ± 1.0 days, an interval termed the lag period (Astheimer et al. 1979). Albumen synthesis appears to begin at, or just before, completion of the yolk and continues until approximately 1 day before oviposition. During this time, however, the yolk remains in the follicle. Replacement eggs are laid 14.5 ± 1.7 days following egg removal or natural loss. Combining the above information with egg composition data, the daily deposition of lipid and protein from the female into the egg was computed. Evidence from the size distribution of small (<5 mm) primordial follicles suggests that the auklet ovary undergoes a cycle of follicular growth and atresia before a single follicle is selected for RYD. Based on these findings, and the correlation between initiation of spring egg laying and decreased sea surface temperatures for Farallon Island auklets, I suggest that the onset of RYD is modulated by environmental conditions.
A Phylogenetic Analysis of Recent Anseriform Genera Using Morphological Characters
Authors: Livezey Bradley C. 
Published: October 2019

Abstract
A phylogenetic analysis of all Recent genera of the Anseriformes using 120 morphological characters supports much of the current consensus regarding intraordinal relationships. I found that (1) Anseranas should be placed in a monotypic family; (2) Dendrocygna, Thalassornis, geese and swans, and Stictonetta are paraphyletic to the rest of the Anatidae; (3) Cereopsis is the sister group to Anser and Branta, and Coscoroba is the sister group to Cygnus and Olor; (4) Plectropterus is the sister group to the Tadorninae (shelducks) and the Anatinae (typical ducks); (5) the shelducks are monophyletic and include Sarkidiornis (provisionally), Malacorhynchus, Hymenolaimus, Merganetta, and Tachyeres; (6) the tribe "Cairinini" ("perching ducks") is an unnatural, polyphyletic assemblage and is rejected; (7) the dabbling ducks (including the smaller "perching ducks") comprise an unresolved, probably paraphyletic group; (8) tribal monophyly of the pochards (including Marmaronetta and Rhodonessa), sea ducks (including the eiders), and stiff-tailed ducks (including Heteronetta) is confirmed; and (9) the retention of Mergellus and resurrection of Nomonyx are recommended based on clarifications of intratribal relationships. Problematic groups, effects of homoplasy, phenetic comparisons, life-history correlates, biogeographic patterns, and fossil species are discussed, and a phylogenetic classification of Recent genera is proposed.
Female Site Fidelity and Polygyny in the Blackpoll Warbler (Dendroica Striata)
Authors: Eliason Bonita C. 
Published: October 2019

Abstract
From 1980 to 1982, 8-30% of male Blackpoll Warblers (Dendroica striata) studied on Kent Island, New Brunswick, were bigamous each year (x̄ = 16.8%). I tested whether differences in the quality of the breeding situation can give rise to polygynous matings. Five territory parameters and two male parameters were used as measures of quality. Male arrival times were correlated with male mating status and the reproductive success of monogamous females. Territories of bigamous males had more large conifers than did those of monogamous males. Territory parameters did not appear to influence female choices.
Strong site attachment by females may lead them to mate bigamously when few males are available early in the season near the females' former nest sites. The reproductive success of secondary females was not different from that of monogamous females. Any costs of mating bigamously may be offset by increased reproductive success associated with early nest initiation and competitive advantages conferred by site dominance.
Site attachment and return patterns can account for the incidence of polygyny in this population, but probably could not give rise to high levels of polygyny or large harems. More information is needed to evaluate the influence of site fidelity on mating decisions of females in other polygynous passerine species.
Economics of Breeding Territoriality in Male Calliope Hummingbirds
Authors: Armstrong Doug P. 
Published: October 2019

Abstract
Several lines of evidence indicate that the territorial behavior of postbreeding North American hummingbirds can be explained in primarily energetic terms. The territoriality of breeding males, however, may be different in that it may play an important role in courtship. The results of this study on breeding male Calliope Hummingbirds (Stellula calliope) indicated that territoriality could not be explained either directly or indirectly in terms of defense of energy resources. Throughout the 2-month breeding season, flower sampling indicated that males could have obtained energy faster by foraging on nearby undefended areas than by foraging on their territories. In June there were no profitable flowers on the territories, and males did all or nearly all of their foraging away from their territories. In May, when territory nectar availability was fairly high, males did not leave, expand, or shift their territories in response to experimental exclosure of all profitable flowers on those territories. I suggest that males may have preferentially selected territory sites with prominent perches near females' nesting areas, and that these considerations outweighed the potential benefits of defending territories on areas with high-quality nectar resources.
Competitive Interactions within and between Species in a Guild of Avian Scavengers
Authors: Wallace Michael P. , Temple Stanley A. 
Published: October 2019

Abstract
We observed Andean Condors (Vultur gryphus), King Vultures (Sarcoramphus papa), Black Vultures (Coragyps atratus), Turkey Vultures (Cathartes aura), and Crested Caracaras (Polyborus plancus) interacting at 217 animal carcasses at two sites in northern Peru. At 53 carcasses for which we knew order of arrival, Turkey Vultures usually arrived first, Black Vultures second, and condors third. On the basis of our observations of 8,066 aggressive encounters between birds, we constructed dominance hierarchies by calculating the proportion of encounters won by an individual of one species, sex, or age during encounters with an individual of another species, sex, or age. Within each species there was a positive relationship between a bird's dominance and its age. In condors, males dominated females of the same age. Interspecific dominance was correlated positively with body mass. There are convergent similarities between the organizations of guilds of Old and New World vultures.
Incubation Behavior of Emperor Geese Compared with Other Geese: Interactions of Predation, Body Size, and Energetics
Authors: Thompson Steven C. , Raveling Dennis G. 
Published: October 2019

Abstract
The incubation constancy of 11 female Emperor Geese (Chen canagica) was monitored electronically and behavior of both sexes was observed during incubation recesses in 1983 and 1984 at Kokechik Bay, Alaska. Average nest attentiveness of female Emperor Geese was 99.5% during 4,800 h of monitored incubation time. Recesses averaged (±SE) 13.3 ± 0.8 min, and modal recess length was 8 min (n = 107). Recess frequency was 0.54/day. This high degree of nest attentiveness exceeded that reported for any goose species. Nest attentiveness did not vary significantly through the incubation period, but increased in the last 3 days, probably in response to embryo noises and pipping. Most recesses (45%) occurred between 1200 and 1800, the warmest portion of the day. There were no significant differences in recess length at different times of day, however, and recess duration and frequency were not related to differences in daily temperature or wind speed. Females fed for only 14% of the time during their infrequent and brief recesses. Most time (43%) during recesses was spent preening and bathing. Males were alert for 49% of the time females were on recess but were present during only 56% of recesses, reflecting their relative lack of attendance during incubation. Behavior of females during recesses when males were absent did not differ significantly from when males were present.
The high incubation constancy, loss of body mass during incubation (20.7%), and relatively large average clutch size (5.2) indicate that Emperor Geese arrive on nesting grounds with an extremely high level of endogenous reserves relative to other geese. Clutch size and incubation behavior also represent trade-offs in energy investment related to body size, egg size, food availability, and feeding needs during incubation. Generally, larger species or subspecies of geese depend more on endogenous reserves than do smaller forms. We believe, however, that this relationship is not satisfactorily explained just by energetic constraints related to body size because Emperor Geese were more attentive to incubation than even larger goose species. Emperor Geese usually can defend their nests from arctic foxes (Alopex lagopus) but, when on incubation recesses, are apparently less efficient in defense against avian predators than sympatric-nesting smaller geese. These smaller species are more vulnerable to foxes but more agile and effective against avian predators. The incubation constancy of geese results from an interaction of predation pressures related to body size and defense capabilities.
Signaling Subordinate and Female Status: Two Hypotheses for the Adaptive Significance of Subadult Plumage in Female Tree Swallows
Authors: Stutchbury Bridget J. , Robertson Raleigh J. 
Published: October 2019

Abstract
Delayed plumage maturation in males is relatively common among North American passerines, but the Tree Swallow (Tachycineta bicolor) is one of few species in which 1-yr-old females have a distinct subadult plumage. Although they are reproductively mature, most subadult females do not breed in their first year because of intense intrasexual competition for nesting sites. Early in the season, subadult female floaters explore for recently vacated nest sites. The subadult plumage of young females could be adaptive by communicating their low threat to residents, thereby decreasing the cost of this exploration.
To determine whether resident aggression depends on intruder color, we observed live intrusions and conducted model presentations. When the resident female was out of sight or did not respond to intruders, resident males were significantly less aggressive toward subadult females than toward adult intruders in both the nest-building/egg-laying and incubation stages. Early in the season, resident females were equally aggressive toward subadult female and adult intruders. When presented simultaneously with adult and subadult female models, resident males were always more aggressive toward the adult model, whereas females were aggressive toward either model.
We propose two hypotheses for the adaptive significance of subadult plumage in female Tree Swallows: subordinance signaling and sex signaling. Our results suggest that subadult females may reduce resident aggression by signaling their female status to resident males, rather than by signaling their subordinate status to resident females.
The Function of Delayed Plumage Maturation in Male Black-Headed Grosbeaks
Authors: Hill Geoffrey E. 
Published: October 2019

Abstract
I used data from two breeding populations of Black-headed Grosbeaks (Pheucticus melanocephalus) in central New Mexico to test alternative hypotheses regarding the function of delayed plumage maturation in male passerines. Yearling male grosbeaks displayed a wide range of subadult plumage types, but most individuals were intermediate in appearance between adult males and females. Subadult male grosbeaks arrived on the study sites about 2 weeks after adult males, with no tendency for individuals with brighter or duller plumage to arrive first. Only a few of the most brightly plumaged subadult males defended territories and attracted females; most were nonterritorial floaters. All territories of subadult males were positioned outside clusters of adult male territories with few total neighbors. When I removed adult males from their territories, the territories remained empty. These results are not consistent with predictions of the female-mimicry hypothesis, but they are in accord with those of the cryptic hypothesis.
Male Parental Care and Extrapair Copulations in the Indigo Bunting
Authors: Westneat David F. 
Published: October 2019

Abstract
Levels of parental care by male Indigo Buntings (Passerina cyanea) were predicted to be lower and the tendency to pursue extrapair matings greater when (1) the opportunity of additional matings (extrapair copulations) was high, (2) the male was cuckolded, and (3) the clutch or brood size was small. Observations of male care revealed that approximately 10% of all males fed nestlings at least once, whereas more than 30% fed fledglings. Males in their first breeding season were never seen feeding young. Males made more trips off their territories when females were fertilizable on nearby territories, but other measures of parental care (feeding young and time spent within 10 m of nest) were not affected. Cuckolded males (known through genetic analyses of parents and offspring) tended to feed young less often, but forayed off their territories significantly less than apparently uncuckolded males. Finally, males with small clutches or broods gave slightly, but not significantly, less care than males with large clutches or broods. These results suggest that the relationship between mating effort and parental effort is complicated by the presence of extrapair copulations as a type of mating effort, and that factors not included in current theory on parental care might influence a male's parental care.
The Beached-bird Assemblage of a Highly Saline Lake and Its Relevance for Reconstructing Paleoenvironments
Authors: Jehl Joseph R. 
Published: October 2019

Abstract
The beached-bird deposits of saline (80-90%) Mono Lake, California, are dominated by Eared Grebes (Podiceps nigricollis) and California Gulls (Larus californicus), which together comprise 95% of the specimens. Nevertheless, the diversity of waterbirds in these deposits is high (31 species), because mortality is high among migratory species that are poorly adapted to saline environments. The composition of the Mono Lake assemblage differs markedly from local Pleistocene faunas that accumulated in fresh or slightly saline habitats.
Site Fidelity and Survival Differences between Two Groups of New World Red Knots (Calidris canutus)
Authors: Harrington Brian A. , Hagan John M. , Leddy Linda E. 
Published: October 2019

Abstract
During the boreal winter, New World Red Knots (Calidris canutus rufa) principally occupy two areas widely separated in latitude. The larger group of approximately 100,000 birds is distributed along the Patagonian Atlantic coast, the smaller group of about 10,000 along Florida's Gulf coast. Resightings of banded individuals showed no interchange between these groups. The annual survival rate of knots marked in Florida is twice that of marked knots that winter in Patagonia. During northward migration Florida knots were sighted significantly less often at a major New Jersey stopover site than knots marked in Argentina. Whether this segregation is maintained during the breeding season is unknown. Wing and culmen lengths did not differ between the groups. The higher survival of individuals from the smaller Florida group, which presumably migrates a much shorter distance than the Argentina birds, runs counter to current evolutionary theories on the benefits of migration.
Forelimb Joint Mobility and the Evolution of Wing-Propelled Diving in Birds
Authors: Raikow Robert J. , Bicanovsky Lesley , Bledsoe Anthony H. 
Published: October 2019

Abstract
We measured wing joint mobility in penguins, alcids, diving-petrels, and non-diving fliers. Great reduction in mobility of the intrinsic wing joints was found in penguins, but not in alcids or diving-petrels. This reduction is correlated with simplification of the intrinsic wing musculature. In contrast, alcids and diving-petrels, which use their wings in both air and water, retain the full functional capacities for flight. Movement through the air probably requires a capability for subtle and varied motions, forces, and shape changes that preclude stiffening and simplification of the wing. Hence, the conversion of an aerial wing to a flipper, as in penguins, must be possible only after the evolutionary loss of flight.
An Early Condor-Like Vulture from North America
Authors: Emslie Steven D. 
Published: October 2019

Abstract
A new genus and species of condor-like vulture (Ciconiiformes: Vulturidae) is described from the middle Miocene (Barstovian) of North America and is the earliest condor now known in the New World. The fossil record at present indicates that the Vulturidae originated in the Old World, but diversified in the New World. Large body size in vultures developed in North America at least 4 million years (Ma) earlier than thought previously, and the condors probably evolved in North America. Condors were most diverse in the late Pleistocene but are now near extinction.
Reproductive Success of Hand-Reared vs. Parent-Reared Cockatiels (Nymphicus hollandicus)
Authors: Myers S. A. , Millam J. R. , Roudybush T. E. , Grau C. R. 
Published: October 2019

Abstract
We studied the influence of early rearing experience on the reproductive success of Cockatiels (Nymphicus hollandicus) by force-pairing somatically mature birds that had been either hand-reared (H) or parent-reared (P) from hatch to 6 weeks of age. Pairs of H-males and H-females, H-males and P-females, P-males and P-females, or P-males and H-females were encouraged to breed by providing nest-boxes and exposing pairs to a sexually stimulatory environment. Hand-rearing produced gender-specific effects that greatly affected reproductive success. Pairs containing H-females were more likely to lay eggs and laid more eggs than pairs with P-females but often laid them on the cage floor rather than in nest-boxes, reducing hatching success. Pairs containing H-males were less likely than pairs with P-males to produce fertile eggs, inspect nest-boxes, or lay eggs in nest-boxes. Fledging occurred only in pairs containing P-males. Early rearing experience is important for males to learn characteristics of the opposite sex, and for males and females to learn characteristics of nest-sites.