bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diet–Feather Stable Isotope (δ15N and δ13C) Fractionation in Common Murres and Other Seabirds
Authors: Becker Benjamin H. , Newman Scott H. , Inglis Susan , Beissinger Steven R. 
Published: September 2019

Abstract
We measured the fractionation of stable nitrogen (δ15N) and carbon (δ13C) isotopes in the breast and primary feathers of 11 Common Murres (Uria aalge) maintained on a diet of capelin (Mallotus villosus). Diet–feather δ15N fractionation from delipidated capelin muscle to murre feathers was 3.6‰ ± 0.2‰ in breast feathers and 3.7‰ ± 0.2‰ in primary feathers. Fractionation of δ13C was 2.5‰ ± 0.2‰ in breast feathers and 1.9‰ ± 0.3‰ in primary feathers. Prey–feather fractionation (for delipidated, muscle-only prey samples) for nine other species of seabirds ranged from 3.0‰ to 4.6‰ for δ15N and 0.1‰ to 2.5‰ for δ13C. Studies that did not remove lipids from prey samples showed higher δ15N and δ13C fractionation, and those that used whole prey items rather than muscle tissue alone showed higher δ15N fractionation. We suggest that: (1) prey samples be delipidated to facilitate interpretation of δ13C fractionation, (2) high interstudy and interspecific variation in δ13C makes species-specific studies essential, and (3) use of muscle tissue rather than whole bodies of fish will minimize unexplained variation in δ15N fractionation.
Phylogeography and Patterns of Differentiation in the Curve-Billed Thrasher
Authors: Rojas-Soto Octavio R. , De Los Monteros Alejandro Espinosa , Zink Robert M. 
Published: September 2019

AbstractRecent mitochondrial DNA (mtDNA) and morphological studies suggest that the Curve-billed Thrasher (Toxostoma curvirostre) consists of three historical groups, corresponding to the subspecies curvirostre and palmeri and a new taxon distributed in Oaxaca and Puebla. Previous mtDNA analysis did not include the subspecies T. c. insularum found on Tiburon Island (Sonora, Mexico). We collected new samples to address the distinctiveness of the three groups, to explore possible contact between the curvirostre and southern clades, to clarify the status of T. c. insularum, and to explore population histories of the major clades. Our mtDNA results confirm the existence of three major haplotype clades, which represent either two or three species depending on the species concept used. We interpret the occurrence of two mismatched haplotypes in Puebla and Oaxaca as recent gene flow. Haplotypes from Tiburon Island were intermixed within the palmeri clade, thereby failing to support the subspecies T. c. insularum. In contrast, principal components analysis of morphological data showed that insularum was distinct and, given the lack of mtDNA distinctiveness, suggests rapid phenotypic evolution on the island. The molecular data suggest that the widespread curvirostre clade has undergone recent population growth, whereas the other two clades appear to have been more stable.
Nest Reuse by Eastern Kingbirds: Adaptive Behavior or Ecological Constraint?
Authors: Redmond Lucas J. , Murphy Michael T. , Dolan Amy C. 
Published: September 2019

AbstractThe reuse of old nests by open-cup nesting passerines is a seemingly rare but potentially adaptive behavior if, as a consequence, females begin to breed earlier, lay larger clutches, or fledge more young. We report an unusually high rate of nest reuse (~10% of 341 nests) for Eastern Kingbirds (Tyrannus tyrannus) breeding at Malheur National Wildlife Refuge, Oregon. We found no difference in availability of nesting habitat or food abundance in territories in which nests were and were not reused. We also found no support for the hypotheses that kingbirds benefited from nest reuse by breeding earlier, laying larger clutches, or fledging more young, and, contrary to expectations, females that reused nests laid significantly smaller eggs than females who built their own nests. Nest reuse was independent of age: a roughly equal number of females for which we had multiple years of data both reused nests and built new nests, but at different points in their lives. Competition for nest sites seems high at Malheur National Wildlife Refuge because many open-cup nesting species utilize similar nest sites in the limited zone of riparian vegetation. A shortage of high-quality nest sites, coupled with interspecific competition, may underlie the high frequency of nest reuse in this kingbird population.
Variation and Individuality in Display-Flight Calls of Male Piping Plovers
Authors: Sung Ha-Cheol , Miller Edward H. 
Published: September 2019

AbstractIn this first study of vocal individuality in the Charadriidae, we describe vocal variation in the endangered Piping Plover (Charadrius melodus). We studied a long-distance advertisement call given by breeding males during aerial displays, because functionally similar vocalizations of scolopacids are known to be individualistic. We analyzed recordings of 10 breeding males on Prince Edward Island, Canada, made in 1998 and 1999. Calls varied substantially among males: variance among males (in one-way ANOVAs) averaged 61% of the total variance across variables, similar to two scolopacid species. Males were distinguishable from one another even on the basis of single calls. However, discrimination ability (classification success) improved substantially when multiple-call averages per male were used; this approach more realistically represents how plovers experience one another's calls. Calls of two males changed little over days to weeks. In future work, individual identification can be improved by using averages from multiple calls. To improve techniques for application to the Piping Plover, we recommend research on marked individuals of common related species, which share many acoustic homologies.
Willow Flycatcher Nonbreeding Territory Defense Behavior in Costa Rica
Authors: Sogge Mark K. , Koronkiewicz Thomas J. , Van Riper Charles , Durst Scott L. 
Published: September 2019

Abstract
We studied the intraspecific territorial defense behavior of wintering Willow Flycatchers (Empidonax traillii) in Costa Rica using a randomized playback experiment that exposed male and female birds to recordings of Willow Flycatcher songs and calls, Lesser Ground Cuckoo (Morococcyx erythropygius) vocalizations, and random noise. Flycatchers of both sexes responded most strongly to simulated conspecific territory intrusion, and the agonistic behaviors that we observed were similar to those seen during natural intraspecific encounters in winter. Both males and females engaged in song and aggressive behaviors in defense of territories, and there was no significant difference between the sexes in scored agonistic responses. The similarity between the sexes in intraspecific territorial defense behaviors and aggressiveness may account for both sexes of flycatchers using the same habitats at our study sites in Costa Rica, and wintering females defending territories against males. The Willow Flycatcher, a sexually monomorphic species, differs in this way from a number of sexually dimorphic passerines, in which behaviorally dominant males occur in more optimal winter habitats.
Measuring Habitat Quality: A Review
Authors: Johnson Matthew D. 
Published: September 2019

AbstractAbstract. Understanding habitat quality for birds is crucial for ecologists and managers, but few papers have explored the advantages and disadvantages of different ways to measure it. In this review I clarify terminology and distinguish habitat quality from related terms, differentiate habitat quality at the levels of individual birds and populations, and describe different field methods for measuring habitat quality. As much as feasible, biologists concerned with habitat quality should emphasize demographic variables while recognizing that reproduction, survival, and abundance may not all be positively correlated. The distribution of birds can also reveal habitat quality (e.g., through patterns of habitat selection), but researchers should first investigate how closely their subjects follow ideal distributions because numerous ecological factors can lead birds to select poor and avoid rich habitats. Measures of body condition can provide convenient measures of habitat quality, but to be useful they must be a consequence, rather than a cause, of habitat selection. Habitat ecologists should use caution before relying on shortcuts from more labor-intensive demographic work. To increase the reliability of our habitat quality measurements, we should work to develop new methods to assess critical assumptions of nondemographic indicators, such as whether birds follow ideal distributions under natural conditions and whether spatial variation in body condition manifests in differential fitness.
Expected Effects of Correlated Habitat Variables on Habitat Quality and Bird Distribution
Authors: Kristan William B. 
Published: September 2019

Abstract
Abstract. Habitats are composed of multiple variables, each of which may affect one or more population demographic rates. The patterns of correlation among habitat variables can introduce correlations among demographic rates, even if any single habitat variable affects only a single demographic rate and is independent of others. I present a simple model in which habitat is composed of two continuous habitat variables, one of which affects fecundity but not survival, and the other of which affects survival but not fecundity, such that correlations between survival and fecundity are due exclusively to correlations between the habitat variables. When individuals are able to select habitat with complete information about habitat quality, habitat selection always leads to higher growth rates at small population sizes. With complete information about habitat quality, patterns of distribution and population growth rates are strongly affected by the correlation between habitat variables. In contrast, when individuals have information about only fecundity or survival but not both, distributions become insensitive to correlations among habitat variables, which can lead to an ecological trap. This simple model demonstrates why explicitly distinguishing between habitat choices and the consequences of choices will be necessary if the complex interplay between habitat structure, habitat choice, and habitat quality is to be fully understood.
Consequences of Habitat Utilization by Nest Predators and Breeding Songbirds Across Multiple Scales in an Urbanizing Landscape
Authors: Marzluff John M. , Withey John C. , Whittaker Kara A. , David Oleyar M. , Unfried Thomas M. , Rullman Stan , Delap Jack 
Published: September 2019

Abstract
Abstract. Nest predation may influence habitat selection by birds at multiple spatial scales. We blended population and community ecology to investigate this possibility for 15 species of forest songbirds and their diurnal nest predators (corvids and sciurids) in 28 1 km2 sites near Seattle, Washington, from 1998 to 2004. We determined whether songbirds were positively or negatively associated with nest predators at three spatial scales, and whether their co-occurrence affected reproductive success. At the largest ‘neighborhood’ scale (1 km2 areas that included suburban and exurban development and second-growth forest remnants), nest predators and their prey were positively or negatively correlated according to general species-specific habitat associations. At the intermediate ‘forest patch’ scale (among remnant forested areas 0.5 to 70 ha), associations between predators and prey were generally weak. At the smallest ‘within patch’ scale (multiple 50 m radius survey plots within each forest patch), some songbird species avoided areas with greater predator use, particularly by Steller's Jays (Cyanocitta stelleri). Failed nests and territories tended to be in locations of higher predator occurrence (especially of corvids) than successful ones, but at the largest 1 km2 neighborhood scale relative abundance of nest predators was not correlated with the fate of nesting attempts or annual reproductive success. Reproductive success was generally high, with 52% of all nests and 49% of all territories fledging at least one young (for all species and years combined). Nest predation influenced some species' use of resources, but was not a strong influence on overall reproductive success or community structure.
Seasonal Interactions, Habitat Quality, and Population Dynamics in Migratory Birds
Authors: Ryan Norris D. , Marra Peter P. 
Published: September 2019

AbstractAbstract. Historically, studies of habitat selection have focused on quantifying how current patterns of habitat occupancy influence condition and survival within a season. This approach, however, is overly simplistic, especially for migratory birds that spend different periods of the year in geographically distinct places. Habitat occupancy and the resulting condition of individual birds is likely to be affected by events in the previous season, and the consequences of habitat occupancy will influence individuals and populations in subsequent seasons. Thus, for migratory birds, variation in habitat quality (and quantity) needs to be understood in the context of how events interact throughout periods of the annual cycle. Seasonal interactions can occur at the individual level or population level. Individual-level interactions occur when events in one season produce nonlethal, residual effects that carry over to influence individuals the following season. Population-level interactions occur when a change in population size in one season influences per capita rates the following season. We review various methods for estimating seasonal interactions and highlight a number of examples in the literature. Using a variety of techniques, including intrinsic and extrinsic markers, the vast majority of studies to date have measured seasonal interactions at the individual level. Obtaining estimates of density and changes in per capita rates across multiple seasons to determine population-level interactions has been more challenging. Both types of seasonal interactions can influence population dynamics, but predicting their effects requires detailed knowledge of how populations are geographically connected (i.e., migratory connectivity). We recommend that researchers studying habitat occupancy and habitat selection consider how events in previous seasons influence events within a season.
What is a Winter Floater? Causes, Consequences, and Implications for Habitat Selection
Authors: Brown David R. , Long Jennifer A. 
Published: September 2019

AbstractAbstract. In migrant birds, winter social systems reflect strategies of habitat use. The best-studied strategy is that of a fixed home range or territory. Alternative strategies to holding a territory, such as floating and flocking behaviors, suggest different processes of habitat selection. Whereas flocking, like territoriality, is a well-studied social strategy, solitary nonterritorial (floater) behavior is difficult to study and is thus poorly understood in terms of its causes, consequences, and implications for habitat selection. Floaters are individuals of a primarily stationary population which move over large areas compared to the average home range size. We review evidence of the causes, consequences, and frequency of winter floating behavior, focusing primarily on migrant songbirds. We also address the endocrine basis of alternative behavioral strategies by presenting results from aviary-based dominance trials with Hermit Thrushes (Catharus guttatus). Results from this study and others suggest that the adrenocortical response to social stress plays a key role in both the proximate and ultimate causes of floating behavior. Because winter floating behavior exists in many migrant songbird species, better understanding of winter floaters may be important for population modeling and conservation planning.
Egg Mass Influences Nestling Quality in Tree Swallows, But There is no Differential Allocation in Relation to Laying Order or Sex
Authors: Whittingham Linda A. , Dunn Peter O. , Lifjeld Jan T. 
Published: September 2019

AbstractAbstract. Maternal allocation of resources to eggs and nestlings can potentially have a profound influence on offspring phenotype and fitness. However, it is often unclear how much of the variation in offspring quality is due to maternal or environmental effects. We examined the influence of maternal and environmental effects on egg mass and nestling quality (growth and immune function) in Tree Swallows (Tachycineta bicolor). There was no evidence that the allocation of maternal resources to eggs varied with laying order or offspring sex. Thus, there was no evidence of adaptive maternal allocation to eggs in terms of mass. Instead, egg mass in Tree Swallows appeared to be influenced primarily by ambient temperature during egg formation and differences among females. Nonetheless, female Tree Swallows were likely to realize substantial benefits from producing larger eggs because those young were larger at hatching and grew faster. Furthermore, nestlings that grew faster had a stronger immune function at 11 days of age. Our results suggest that the positive relationship between nestling growth and survival may be due, in part, to the effects of an enhanced immune response.
Seed Preferences of Wintering Henslow's Sparrows
Authors: Dimiceli Jennifer K. , Stouffer Philip C. , Johnson Erik I. , Leonardi Claudia , Moser Edgar B. 
Published: September 2019

Abstract
Abstract. The Henslow's Sparrow (Ammodramus henslowii), a species of conservation concern, winters primarily in longleaf pine (Pinus palustris) forest ecosystems in the southeastern U.S. These pine savannas have been reduced to 5% of their former range, with remaining patches requiring active management with fire to maintain characteristic structure and plant diversity. Wintering Henslow's Sparrow abundance tracks growing-season fires; bird abundance peaks in the winter following burning, then declines in subsequent winters. Fire also determines dominant plant species, suggesting that Henslow's Sparrows may respond to abundance of preferred seeds. To determine diet preferences of Henslow's Sparrows, we tested seeds from eight species of native plants from southeastern Louisiana pine savannas, including species common in the first winter after burning (‘fire grasses’) and species that increase in abundance in the second and subsequent winters after burning. Seed consumption by individual birds differed considerably, suggesting that Henslow's Sparrows forage on a variety of resources in the highly diverse savannas. Henslow's Sparrows preferred fire grasses, especially Muhlenbergia expansa (cutover muhly). They also preferred Dichanthelium angustifolium (needleleaf rosette grass), a species more common in the second year after burning, but consumed relatively little of the sedges Rhynchospora plumosa (plumed beaksedge) and R. gracilenta (slender beaksedge), species common in the second winter after fire. Birds consumed almost none of the ubiquitous grass Schizachyrium scoparium (little bluestem). These results suggest that preferred seeds may include those that are most common in the first winter after burning, but that some suitable seeds are available for at least another winter.
Mitochondrial DNA Variation and Phylogeography of the Eastern and Western Screech-Owls
Authors: Proudfoot Glenn A. , Gehlbach Frederick R. , Honeycutt Rodney L. 
Published: September 2019

AbstractAbstract. Sequences of the mitochondrial cytochrome b gene (930 base pairs) were used to examine patterns of variation within and between Eastern (Megascops asio) and Western (M. kennicottii) Screech-Owls, and to assess taxonomic affinity of Flammulated Owls (Otus flammeolus) and Whiskered Screech-Owls (M. trichopsis). Analyses support monophyly of the New World Megascops, a sister-group relationship between O. flammeolus and New World forms of Megascops, rather than with Old World Otus, and a closer relationship between the mostly North American M. trichopsis and South American Megascops than between M. trichopsis and North American Megascops. Megascops asio and M. kennicottii formed two distinct monophyletic clades, supporting species-level designations as suggested by morphology and song. Evidence for distinctive subspecies of eastern and western forms of screech-owls was less compelling. In the M. asio group, M. a. mccallii was the only subspecies with a unique haplotype; other subspecies within M. asio were phylogenetically indistinguishable. Subspecies within M. kennicottii were partitioned into three geographic groups, and differences are probably the result of barriers to gene flow (e.g., mountains above 2300 m), which are more pronounced throughout the distribution of M. kennicottii than in the distribution of M. asio.
Age-Related Survival and Behavior of Snowy Plover Chicks
Authors: Colwell Mark A. , Hurley Susan J. , Hall James N. , Dinsmore Stephen J. 
Published: September 2019

AbstractAbstract. Precocial young often experience high mortality prior to achieving flight, especially in the first days after hatching. We quantified relationships between chick age, survival, behavior, and response to natural and anthropogenic danger for the threatened Western Snowy Plover (Charadrius alexandrinus nivosus) in coastal northern California, USA. Plover chicks were most likely to die in the first three days of their 28-day prefledging period, especially on sandy ocean beaches compared to coarser substrates of river habitats. Chick survival in both habitats increased across the ∼120-day chick-rearing period. Improved survival of older chicks coincided with an age-related reduction in brooding and increased distance from the tending parent, which was not related to season. Lower survival of younger chicks was correlated with a tendency to lie motionless when approached by humans; nearly all older chicks responded to human approach by running to evade danger. Chicks of all ages were more likely to lie motionless when potential avian predators flew nearby. Age-dependent survival of Snowy Plover chicks paralleled a trend of increasing development, thermal independence from adults, and capability of evading predators.
The Duetting Behavior of Pacific Coast Plain Wrens
Authors: Cuthbert Jessica L. , Mennill Daniel J. 
Published: September 2019

Abstract
Abstract. We provide the first detailed analysis of the vocal behavior of Pacific coast Plain Wrens (Thryothorus modestus modestus). Male Plain Wrens sing two categories of song phrase; one phrase is given as a solo song or duet introduction (I-phrases), while the other is sung primarily during duets (M-phrases). Females sing only one category of song phrase, usually during duets (F-phrases). Both sexes have repertoires of their respective song categories. Plain Wren duets show extreme temporal coordination: duets typically begin with male I-phrases, which are followed by the rapid alternation of female F-phrases and male M-phrases. These patterns are congruent with the solo and duet singing behavior of a sister taxon to the Plain Wren, the Canebrake Wren (Thryothorus modestus zeledoni). Our analyses of Plain Wren songs and duets reveal pronounced differences between males and females and contribute to our understanding of the complex duetting behavior of Thryothorus wrens.