bluuebunny/crossref_metadata_2025_split huggingface dataset:
Weights, Breeding, and Survival in European Sparrowhawks
Authors: Newton I. , Marquiss M. , Village A. 
Published: October 2019

Abstract
No significant diurnal variation in mean weight was detected in trapped European Sparrowhawks (Accipiter nisus). Weights of males fluctuated rather little through the year, but were highest in March and lowest in August. During the breeding cycle, males lost weight slightly in the prelay/early laying periods, when they were feeding females in preparation for egg production, and in the late nestling/postfledging periods, when they were feeding large young. Weights of females fluctuated greatly during the year: they were highest in May at the time of egg laying and lowest in August at the end of breeding. Females increased in weight by 40-50 g (15%) in the 10-20 days before laying; lost about 20 g over the laying period, on average; maintained high weight through much of incubation; and lost weight during the nestling period. The main functions of the extra body reserve are probably to buffer the female against temporary food shortages during incubation and to enable her to feed the chicks preferentially in the nestling period. Females that did not lay eggs remained low in weight throughout the early part of the breeding season and were then significantly lighter than breeders. Moreover, females that laid large clutches were heavier throughout the prelaying and laying periods than were females that laid small clutches, and females that subsequently hatched their eggs started incubation at a significantly greater weight than did those that deserted their eggs. We suggest that clutch size and breeding success are dependent on the female being able to maintain high weight during the periods she is dependent on the male for food and, hence, on the hunting success of the male.
First-year birds of both sexes weighed less than adults throughout the year and were especially light during their first 2 months of independent life. This was probably a period of high mortality, especially in males, in which a clear relationship emerged between weight and survival prospects.
Changes in Song Dialect Distributions and Microgeographic Variation in Song of White-Crowned Sparrows (Zonotrichia leucophrys nuttalli)
Authors: Trainer Jill M. 
Published: October 2019

Abstract
Multivariate analysis and analysis for spatial autocorrelation of 21 frequency and time characteristics of the songs of White-crowned Sparrows (Zonotrichia leucophrys nuttalli) showed that within a dialect area the songs of neighboring males were no more similar to one another than to the songs of non-neighbors. This result refutes one prediction of the hypothesis that song dialects are maintained because males copy the songs of neighbors to gain an advantage in territorial defense or mate attraction. Historical events were important in producing changes over 10 yr in dialect distributions in an area of secondary contact between two dialects. The dialect distributions changed as the sparrow population invaded a new area where the vegetation had been modified, and the sparrows disappeared from a drought-affected area. The basic structure of the dialects did not change in 18 yr, and the fine structure, measured by 21 variables, did not differ between the 2 yr sampled. In 10 yr the two dialects did not blend to form an intermediate dialect.
Competition for Nesting Space among Peruvian Guano Birds
Authors: Duffy David Cameron 
Published: October 2019

Abstract
In the mid-1940's, Peruvian managers greatly increased the nesting space available to the three principal surface-nesting species of the Peruvian Coastal Current: the Guanay Cormorant (Phalacrocorax bougainvillii), the Peruvian Booby (Sula variegata), and the Peruvian Brown Pelican (Pelecanus occidentalis thagus). The combined populations of these three species increased from 8 to 20 million birds. The annual rate of increase of the population rose from 8 to 18%. The three species appear to have evolved in the face of a shortage of nesting space. They have not diverged in their respective breeding seasons. Each species has habitat preferences for nesting, but the overlap is great. The booby and cormorant compete through a "scramble" to occupy space before it is settled by the other species. Neither can displace the other from nest sites. The pelican is dominant over the other two in aggressive interactions and frequently usurps their nests. Pelicans are apparently confined to nesting in level areas, whereas the other two species can nest on a greater range of gradients.
Despite the facts that nesting space is limited and that its scarcity has a demonstrated effect upon the combined populations, interspecific competition for nesting space was difficult to document. Interspecific aggressive interactions were few and involved only a small percentage of the three populations. The individuals most affected by competition, those denied nesting space, were displaced from the area of competition and were thus less accessible for study.
Growth of the Wedge-Tailed Shearwater in the Hawaiian Islands
Authors: Pettit Ted N. , Byrd G. Vernon , Whittow G. Causey , Seki Michael P. 
Published: October 2019

Abstract
Growth studies of a tropical seabird, the Wedge-tailed Shearwater (Puffinus pacificus), were conducted over 3 yr at three locations in Hawaii. Basic growth patterns of body dimensions are described. The range of asymptotes and maximal recorded weights suggests that feeding and the availability of food may influence growth from year to year and in different colonies within the same year.
The Hindlimb Musculature of the White-Fronted Amazon (Amazona albifrons, Psittaciformes)
Authors: Berman Susan L. 
Published: October 2019

Abstract
The hindlimb musculature of six specimens of Amazona albifrons was dissected in order to (1) provide a detailed myological description, (2) provide a preliminary study and basis for a systematic analysis of the Psittaciformes, and (3) point out any myological peculiarities that might be associated with their unusually manipulative feet. Notable features include a peculiar positioning of M. extensor brevis digiti IV, a previously undescribed muscle to digit III, a peculiar arrangement of the short extensors of the hallux, and a branch of M. extensor digitorum longus to the hallux. These features are believed to be associated either with the zygodactyl digit configuration or the requirement of finer control over the individual digits.
Flight Energetics of Free-Living Sooty Terns
Authors: Flint Elizabeth N. , Nagy Kenneth A. 
Published: October 2019

Abstract
The CO2 production of free-ranging Sooty Terns (Sterna fuscata) was measured using doubly labeled water (HTO-18). Metabolic rate during flight was determined to be 4.8 times standard metabolic rate (SMR). This value is much lower than estimates of flight metabolism predicted from previously published equations. Observations of these birds at sea indicate that flapping flight predominated at the windspeeds (0-5 m/s) that prevailed during our measurement periods, so factors other than gliding must account for the comparatively low flight metabolism we measured. Sooty Tern flight metabolism is similar to that of some other birds, such as swallows and swifts, that also have high aspect ratios and low wing loadings.
Food Passage and Intestinal Nutrient Absorption in Hummingbirds
Authors: Karasov William H. , Phan Duong , Diamond Jared M. , Carpenter F. Lynn 
Published: October 2019

Abstract
We studied adaptations of digestive physiology that permit Rufous (Selasphorus rufus) and Anna's hummingbirds (Calypte anna) to absorb sugar-water meals rapidly and efficiently. As measured with soluble markers, transit times (<15 min) and mean retention times (ca. 48 min) of meals in the hummingbird digestive tract are brief compared with values for most other vertebrates. Glucose is extracted with an efficiency of 97%. We describe a new method, employing double isotope dilution, for measuring crop-emptying kinetics. Based on this method, the crop empties half of a meal in ca. 4 min and all of the meal in 15-20 min. Rufous and Anna's hummingbirds may be energy maximizers limited by crop emptying times, rather than foraging-time minimizers. This would explain why hummingbirds spend a majority of each hour sitting rather than feeding.
The intestine's passive permeability to glucose is the lowest of any vertebrate studied to date. This may be an adaptation to prevent solute loss from the blood in the face of high fluid transit rates through the intestine. Active transport accounts for essentially all intestinal glucose absorption. Compared with intestines of other vertebrates, the glucose absorption sites of hummingbird intestines have normal binding constants but are present at extremely high densities. Comparisons of hummingbirds, chickens, and shrikes suggest that intestinal absorption rates for amino acids are independent of trophic habits in birds as in other vertebrate classes, but that sugar absorption decreases in the sequence herbivore > omnivore > carnivore.
The Relationship Between Body Mass and Survival of Wintering Canvasbacks
Authors: Haramis G. M. , Nichols J. D. , Pollock K. H. , Hines J. E. 
Published: October 2019

Abstract
Mass and recapture histories of 6,000 Canvasbacks (Aythya valisineria) banded in upper Chesapeake Bay were used to test two hypotheses: (1) early-winter body mass is associated with the probability of surviving the winter, and (2) early-winter body mass is associated with annual survival probability. Data were analyzed by a binary regression method that treated mass as a continuous variable and estimated parameters to describe a general relationship between body mass and survival probability. Results for adult males, which provided our largest data sets, presented strong evidence that birds with high relative early-winter masses had both greater overwinter and annual survival probabilities. Results of overwinter analyses necessarily are qualified by the alternative explanation of mass-dependent emigration, i.e. the possibility that lighter birds move south in response to cold weather and leave only heavy birds for recapture. Such a phenomenon remains to be documented. Results concerning annual survival probabilities are not vulnerable to this alternative explanation because of the strong fidelity of Canvasbacks at the banding site. Because of small sample size, data were inadequate to permit mass/survival inferences for adult females. Sample sizes were adequate for young Canvasbacks, but the results were less consistent than for adult males. Although early-winter body mass was associated positively with overwinter as well as annual survival for young Canvasbacks in some years, we suspect that the lack of established wintering patterns among these birds may underlie the less consistent result.
The Diet of American Robins: An Analysis of U.S. Biological Survey Records
Authors: Wheelwright Nathaniel T. 
Published: October 2019

Abstract
I present a quantitative description of the diet of American Robins (Turdus migratorius) and consider how food habits (particularly the proportion of fruit eaten and the diversity of individual meals) are influenced by season, habitat, sex, and time of day. The study is based on an analysis of records of stomach contents compiled by the U.S. Biological Survey and the U.S. Fish and Wildlife Service. Across their entire range, robins ate fruits representing over 50 genera and invertebrates representing over 100 families. Diets were diverse even within local regions, and there was no obvious single feeding niche. The major food classes, consumed in every combination, were soft-bodied invertebrates, hard-bodied invertebrates, and fruits. The same taxa (especially fruits of the family Rosaceae and invertebrates of the orders Coleoptera and Lepidoptera) predominated in robins' diets, irrespective of habitat or geographical location, which presumably reflects both selective foraging and the availability of these widespread taxa.
The proportion of fruit (by volume) in the diet was much higher in the fall and winter (median values >90%) than in the spring (<10%); summer values were intermediate. The transition from a diet dominated by invertebrates to a diet dominated by fruits occurred over a 1-2-month period. The number of distinct food items in stomachs, a measure of the species diversity of individual meals, was positively correlated with the fraction of invertebrates in the diet. Thus, at the time of year when robins were dependent on fruits for food, the diversity of their meals was also lowest. The degree of fullness of the stomach showed few consistent trends with season or habitat.
Despite different sex roles and nutritional requirements, male and female robins did not differ in the proportion of fruit in the diet in any month or in any region. Nor did their stomachs contain different numbers of distinct food items, different amounts of food, or a different range or distribution of prey taxa. Habitat was an important variable explaining dietary differences.
The Biological Survey records have unavoidable shortcomings, most notably problems of sampling biases and the inability to correct for differential digestion of food items. Nonetheless, they are a valuable and underused data base for testing hypotheses, generating new questions of ecological interest, and describing in detail the diets of North American bird species.
Effects of Nestling Diet on Growth and Adult Size of Zebra Finches (Poephila guttata)
Authors: Boag Peter T. 
Published: October 2019

Abstract
Manipulation of the diet of Zebra Finch (Poephila guttata) nestlings in the laboratory showed that a low-quality diet reduced growth rates of nine external morphological characters, while a high-quality diet increased growth rates. The growth of plumage characters was least affected by diet, while growth rates of tarsus and mass were most affected. The treatments also produced differences in the adult size of experimental birds, differences not evident in either their parents or their own offspring. Diet quality had the strongest impact on adult mass and tarsus length, while plumage and beak measurements were less affected. Analysis using principal components and character ratios showed that the shape of experimental birds was affected by the experimental diets, but to a minor extent compared with changes in overall size. Significant shape changes involved ratios between fast- and slow-growing characters. The ratios of characters that grow at similar, slow rates (e.g. beak shape) were not affected by the diets. Environmental sources of morphological variation should not be neglected in studies of phenotypic variation in birds.
Experiments on the Control of Deceptive Signals of Status in White-Crowned Sparrows
Authors: Fugle Gary N. , Rothstein Stephen I. 
Published: October 2019

Abstract
We showed previously that crown plumage brightness signals relative dominance ability in White-crowned Sparrows (Zonotrichia leucophrys gambelii). We now test the social-control hypothesis for the evolutionary stability of status signaling against invasion by individuals with brighter crowns than justified by their intrinsic dominance ability. "Cheating" immature females, with crowns painted to resemble bright adult males, and "control" immature females, with crowns painted a typical immature appearance or left unpainted, were released into two separate wild sparrow flocks and into two different captive groups that contained birds of all age and sex classes. In the field experiments, cheaters were more successful than controls in dominance interactions with other immatures; both groups were equally unsuccessful against adults. In the captivity experiments, cheaters generally dominated controls and were more successful than they in interactions with immature males and adult females but not with adult males. Cheaters did not receive more aggression from dominant individuals than did controls in any experiment, and in two experiments they received significantly less aggression. Thus, we found no socially mediated costs for sparrows with deceptive signals. Instead, we showed that immature females that cheat can benefit. The stability of the White-crowned Sparrow signaling system remains unexplained. We discuss the potential influence of predators on individual plumage differences and offer additional hypotheses for the control of deceptive signals.
Yearly and Situational Changes in the Estimate of Repertoire Size in Northern Mockingbirds (Mimus polyglottos)
Authors: Derrickson Kim C. 
Published: October 2019

Abstract
The singing behavior of 4 male Northern Mockingbirds (Mimus polyglottos) was studied during 1980 and 1981. Over 10,000 song bouts (repetition of a particular song type) were analyzed spectrographically. Between 102 and 412 distinct song types were identified for each male in a given year. Many of these song types (25.8-57.4%) occurred only once in this sample of singing behavior. Repertoire size was estimated by fitting an exponential curve to a cumulative plot of distinct song types as a function of consecutive bouts sampled. The resulting asymptote was the estimate of repertoire size. Sequences of at least 50 consecutive bouts were used in estimating repertoire size. The technique of using consecutive bouts was required because of the high proportion of rare song types. Several estimates were made for each male and resulted in mean repertoire size estimates of 100-200 song types for the four males. Long sequences (125-150 bouts) of consecutive bouts are preferred to estimate repertoire size accurately. In addition, the social situation in which the singing behavior occurred can alter significantly the estimate of repertoire size. For example, estimates produced from singing during patrolling or countersinging were smaller than estimates generated from singing while associating with a female.
The repertoire size estimate increased between 1980 and 1981 for 3 of 4 males. The one male not showing an increase spent much time patrolling and interacting with neighboring males before dying early in 1981. These results are consistent with the impression that repertoire size increases with age.
Intersexual Differences in Food Consumption by Hand-Reared Great-Tailed Grackle (Quiscalus mexicanus) Nestlings
Authors: Teather Kevin L. 
Published: October 2019

Abstract
I monitored food consumption by hand-reared Great-tailed Grackle (Quiscalus mexicanus) nestlings to test the hypothesis that males and females consume similar amounts of food but males direct more of their energy into characters that result in greater mass increase. Growth patterns of hand-reared nestlings reflected those of naturally reared nestlings: males were heavier and had longer tarsi, and females had longer 9th primaries on days 6-12 post-hatching. Males, on average, consumed 15.8% more food than females throughout this period; the amount of food consumed per unit mass increase was similar for both sexes. The results suggest there may be substantial cost differences to parents in rearing offspring of different sex. The nestling sex ratio for this and other sexually size-dimorphic species is generally close to one, and Fisher's (1930) theory that differential investment in sons and daughters should result in a skewed sex ratio at the end of parental care is not supported.
Linearity of Geographic Range and Its Possible Effect on the Population Structure of Andean Birds
Authors: Graves Gary R. 
Published: October 2019

Abstract
Geographic ranges of widespread Andean forest bird species are linear, averaging over 300 times longer than they are wide. Among congeneric species, geographic variation in plumage was negatively correlated to the width (W) of their elevational distributions, presumably because narrower distributions are more easily fragmented by barriers to gene flow. The amplitude of a species' elevational distribution may be limited by zonation of resources and by genetic factors that prevent populations from adapting to local environments. Minimum amplitudes may be dictated by demographic consequences.
Coordination of Incubation Routines and Mate Choice in Adélie Penguins (Pygoscelis adeliae)
Authors: Davis Lloyd S. 
Published: October 2019

Abstract
I studied the mating patterns and foraging-trip durations for a colony of Adélie Penguins (Pygoscelis adeliae) over two consecutive breeding seasons. Foraging-trip duration was not predicted by the time spent fasting before leaving the nest, but was consistent with the time remaining until hatching of the chicks. Consequently, foraging trips of pairs that successfully coordinated their incubation routine were complementary. The complementarity was due at least in part to the assortative effects of mate choice. Pairs that successfully coordinated the first three foraging trips remained together the next season; pairs that did not, separated. I argue that Adélie Penguins should retain their mates if partners are synchronous in their arrival at the rookery the next year and that, therefore, pairs unable to coordinate incubation must also be unlikely to coordinate their arrival at the rookery the next season.
Radar and Visual Observations of Autumnal (Southward) Shorebird Migration on Guam
Authors: Williams Timothy C. , Williams Janet M. 
Published: October 2019

Abstract
Several species of shorebirds migrate between eastern Asia and the southern Pacific islands, Australia, and New Zealand. Observations made from Guam (13°25′N, 144°45′E) during autumn 1983 indicate that a significant number of birds take a direct route over the western Pacific Ocean. Radar observations and ground counts of migrants on Guam showed two periods of autumnal migratory activity. The first, largely adult birds, was in August and September. The second, largely juveniles, was in late September and October. Radar indicated that large numbers of birds passed over the island to the south with no evidence of compensation for drift by the easterly winds. Comparison of radar and ground observations on Guam showed that only a small subset of migrants stop on the island, suggesting that some species may make nonstop flights between eastern Asia and the South Pacific.
Morphometrics of Flightlessness in the Alcidae
Authors: Livezey Bradley C. 
Published: October 2019

Abstract
Data collected from skin specimens of the 23 Recent species of Alcidae, skeletal material for Recent and fossil alcids, and published data on body mass and wing area were used to describe the morphometric characteristics of flightlessness in the Great Auk (Pinguinus impennis) and the fossil mancalline auks. A regression equation confirmed a body-mass estimate (5 kg) for P. impennis (Bédard 1969). The size and relatively small wings produced wing-loading of roughly 22 g· cm-2, comparable to those of medium-sized penguins. Multivariate analysis of external measurements underscored the uniquely large size, relatively short wings, and moderately deep bill of Pinguinus compared to other Recent alcids. Analysis of skeletal measurements revealed that the genera of flightless Alcidae (Pinguinus, Mancalla, Praemancalla, and Alcodes) were characterized by relatively short distal wing elements and dorsoventral flattening of all major wing elements, in combination with relatively large core and pelvic dimensions. These differences were most pronounced in Mancalla, moderately developed in Praemancalla, and smallest in Pinguinus. Estimated body mass (1-4 kg) for selected fossil mancallines exceeded the largest flighted alcids (Uria) but was less than for Pinguinus. Pinguinus was a comparatively large piscivore sharing many morphological features with the Razorbill (Alca torda) and murres (Uria spp.). Its flightlessness evidently was a consequence of extreme specialization for pursuit diving, convergent with that of the Spheniscidae. Loss of flight imposed significant requirements on breeding sites and foraging habitats of the Great Auk and presumably the mancallines, and rendered Pinguinus exceptionally vulnerable to human exploitation.