bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sex, Age, and Body Size Distributions of Western Sandpipers During the Nonbreeding Season With Respect to Local Habitat
Authors: Fernández Guillermo , Lank David B. 
Published: September 2019

AbstractWe documented the local density and sex, age-class, and body size distributions of Western Sandpipers (Calidris mauri) among habitats at Bahía Santa María, northwestern Mexico, during the nonbreeding season. Three habitats were recognized: brackish flats, mangroves, and cattail marshes, which we ranked as richest to poorest in food resources and safest to most dangerous in predation danger. Western Sandpiper population structure differed among habitats. Bird densities were highest in brackish flats, the richest and safest habitat, and males and adults of both sexes were overrepresented. In cattail marshes, which appeared to be the poorest and most dangerous habitat, bird densities were lower, and the sex ratio and age ratios within each sex were more even. In mangroves, bird densities were similar to those in cattail marshes, but sex and age ratios were similar to those in brackish flats. Exposed culmen, an index of structural size, was not related to habitat use in either sex. Body mass of immature males was more variable than that of adults among habitats and immature males gained mass throughout the winter. Birds in brackish flats and mangroves were initially heavier, but tended to lose mass, whereas birds in cattail marshes were initially lighter, but tended to gain mass. Mass distributions thus converged in late winter. While the social and ecological causes and significance of differential sex and age-class distributions among habitats remain largely unquantified, evidence from this and previous studies suggests that nonbreeding population structure is a common phenomenon with important implications for migratory shorebirds.
Polygyny and Extra-Pair Paternity in a Population of Southwestern Willow Flycatchers
Authors: Pearson Talima , Whitfield Mary J. , Theimer Tad C. , Keim Paul 
Published: September 2019

Abstract
Although polygyny can potentially increase male reproductive success, the benefits of this strategy could be offset by losses to extra-pair paternity or reduced offspring survival. We developed microsatellite markers to assess the influence of extra-pair offspring (EPO) on reproductive success and paternity in monogamous and polygynous pairs of the facultatively polygynous Southwestern Willow Flycatcher (Empidonax traillii extimus). Based on genotypes of 140 offspring from 56 clutches over six years, 14% of nestlings in our study population were extra-pair offspring, with 23% of all successful nests containing at least one EPO. We found that polygynous males produced 2.11 ± 0.35 offspring per season, compared to 1.15 ± 0.18 for monogamous males. This increased reproductive success was due primarily to the increased number of nests of polygynous males, as the number of offspring per pair did not differ between monogamous and polygynous males. Twenty of the 140 genotyped nestlings were extra-pair offspring. Sires could be assigned to 16 of these; one polygynous male sired two EPO in one nest, two monogamous males sired eight EPO in two nests, and four nonterritorial males sired six EPO in four nests. Overall, these results indicate that in this population, females of polygynous males did not raise a disproportionate number of EPO as a result of the polygynous mating strategy of their mate, and that both territorial and nonterritorial males sired EPO.
Breeding Strategies of a Socially Monogamous Neotropical Passerine: Extra-Pair Fertilizations, Behavior, and Morphology
Authors: Carvalho Carlos B. V. , Macedo Regina H. , Graves Jefferson A. 
Published: September 2019

AbstractBlue-black Grassquits (Volatinia jacarina) are small, granivorous, Neotropical birds that are abundant in central Brazil. During the reproductive season, the socially monogamous males acquire a blue-black plumage and defend very small, clustered territories that resemble leks. They execute a conspicuous courtship display that consists of a leap, revealing white under-wing patches, synchronized with a vocalization. We collected data on the morphology and behavior of banded males and characteristics of their territories to determine how these factors may influence acquisition of mates and nesting. For a second group of birds in the area, we used microsatellite genotyping to test the breeding synchrony hypothesis, which predicts that tropical species that breed synchronously should exhibit high rates of extra-pair fertilization (EPF). We found that males that successfully formed a pair bond differed from unsuccessful males in their behavior, but not in morphological attributes or territory features. Successful males spent more time in their territories, executed displays for longer periods and at greater rates, and their display leaps were higher. These results point to the greater importance of behavior relative to other factors in the successful reproduction of Blue-black Grassquit males. In the second group of birds, EPFs occurred in 63% of 11 nests and involved 50% of the 20 chicks sampled. This exceptionally high incidence of EPF in the small sample analyzed occurred in diverse contexts, including intraspecific parasitism and quasi-parasitism, a rare type of maternity loss where the resident female is parasitized by other females that were fertilized by the resident male. A short and highly synchronized breeding season, clustered breeding in small territories, and granivorous habits may contribute to the high rates of EPF in this tropical species.
Changes in Egg Size and Clutch Size with Elevation in a Wyoming Population of Mountain Bluebirds
Authors: Johnson L. Scott , Ostlind Emilene , Brubaker Jessica L. , Balenger Susan L. , Johnson Bonnie G. P. , Golden Harold 
Published: September 2019

AbstractFew studies have examined how avian life-history traits vary within populations as elevation increases and climate becomes more severe. We compared egg and clutch sizes of Mountain Bluebirds (Sialia currucoides) nesting at two elevations (1500 m and 2500 m above sea level) in the Bighorn Mountains of Wyoming over two years. Eggs laid by females at the high-elevation site were, on average, significantly (6%) smaller in volume than eggs laid by their lower-elevation counterparts. Across elevations, egg size showed a significant positive correlation with female body condition (weight relative to size), and high-elevation females had significantly lower indices of condition than low-elevation females. Temperatures during clutch formation were colder at the high-elevation site, and egg size was negatively related to temperature after controlling for the effects of female condition. Clutches of females at high elevations were, on average, marginally smaller (by 5%, 0.3 eggs) than clutches of low-elevation females. Unlike egg size, clutch size was unrelated to either female condition or temperature during clutch formation. This suggests that, when under energetic or nutritional stress at high elevations, females sacrifice egg size before sacrificing clutch size.
Chick Growth Variability and Parental Provisioning in the Magnificent Frigatebird
Authors: Tobón Emilio , Osorno José Luis 
Published: September 2019

AbstractIn two contrasting breeding seasons, we investigated the effects of provisioning on chick growth and survival of the Magnificent Frigatebird (Fregata magnificens), a socially monogamous, dimorphic seabird that rears a single chick for more than a year, shows specialized feeding techniques, and depends on unpredictable food sources. We hypothesized that chicks of this seabird would increase their chances of survival by varying their growth in relation to food availability. We estimated the amount of food ingested by a chick using electronic scales placed at the nest and recorded feeding rates, growth rate, fledging size, and fledging age. Body mass and bill and ulna lengths were also measured. Not surprisingly, provisioning and growth were higher in the year with apparently higher food availability; however, developmental variables did not show the same pattern. This work shows a clear relationship between provisioning and growth and that growth variability occurs in this species. Understanding the relationship between provisioning and growth provides insight into life histories and elucidates the influence of variation in provisioning on fitness.
Productivity of Black Oystercatchers: Effects of Recreational Disturbance in a National Park
Authors: Morse Julie A. , Powell Abby N. , Tetreau Michael D. 
Published: September 2019

Abstract
National parks in Alaska are generally assumed to be high-quality, undisturbed wildlife habitats. However, these parks attract recreational users, whose presence may reduce the suitability of key habitats for nesting shorebirds. In Kenai Fjords National Park, Black Oystercatchers (Haematopus bachmani) often breed on gravel beaches that are also popular campsites. In this study, we examined the effects of recreational activities in coastal Alaska on reproductive performance of Black Oystercatchers. We monitored survival of nests and chicks on 35 to 39 breeding territories annually during four breeding seasons (2001–2004). Most recreational disturbance on these territories occurred after the peak hatching date of first clutches. Annual productivity was low (average of 0.35 chicks per pair), but was not strongly affected by recreational disturbance. Daily survival of nests varied annually and declined over the season. Our results suggest that nest survival was lower during periods of extreme high tides. Daily survival rate of broods increased over the season and was higher on island than mainland territories, likely due to differences in predator communities. Territory occupancy rate and site fidelity were high; 95% of color-banded oystercatchers returned to the same breeding territory in the subsequent year. We conclude that Black Oystercatchers are resilient to low levels of recreational disturbance. However, in light of projected increases in recreation, we suggest managers move campsites away from the traditional nest sites identified in this study to minimize future disturbances.
Prebasic Molt and Molt-Related Movements in Ash-Throated Flycatchers
Authors: Butler Luke K. , Rohwer Sievert , Rogers Michelle 
Published: September 2019

AbstractWe describe the timing and location of the prebasic molt in the Ash-throated Flycatcher (Myiarchus cinerascens), a hawking insectivore with resident populations in Mexico and migrant populations that breed in the western United States. The timing of fall molt with respect to migration is of particular interest for Ash-throated Flycatchers from the United States because they breed in arid lowland habitats that are probably unproductive in late summer, and because time constraints on molt might force northern populations to leave their breeding grounds before molting. Adults and juveniles depart their breeding grounds to arrive and molt in the region of the Mexican monsoon shortly after the monsoon rains begin. Diminishing food on the breeding grounds and increasing food in the monsoon region seem more important than time constraints for explaining molt-related movements by northern populations, because more southerly breeding birds east and west of the monsoon region also move to the monsoon region to molt. We found age class differences in the timing and duration of molt. In adults the primary molt starts approximately 14 July and requires 76 days to complete, whereas in juveniles, primary molt starts approximately 1 August (18 days after adults) but requires only 50 days to complete. We found no evidence that juveniles molt more primaries simultaneously than adults, so we conclude that the daily growth rate of individual feathers must be higher in juveniles than adults.
Slave to the Tides: Spatiotemporal Foraging Dynamics of Spring Staging Black Brant
Authors: Moore Jeffrey E. , Black Jeffrey M. 
Published: September 2019

AbstractArctic-nesting geese depend on nutrients acquired during spring migration for reproduction, and thus should attempt to maximize nutrient intake while on staging areas. We investigated site use of Black Brant (Branta bernicla nigricans) at an important staging location—Humboldt Bay, California—to determine whether birds selected the most profitable feeding areas available. Migrating Brant feed almost exclusively on eelgrass (Zostera marina), which is restricted in availability due to daily and seasonal tidal cycles. We mapped foraging Brant locations during low tides and collected eelgrass samples to describe food resources in 31 areas in the bay. We used negative binomial regression to evaluate goose densities during different tidal levels and times of season as a function of food biomass and nutrient content, distance from grit sites, and substrate elevation. Results varied by time of season and tidal depth, but Brant densities were positively correlated with eelgrass protein, calcium, and biomass in most analyses. Brant usually fed in the deepest possible areas permitted by tides, and closer to tidal channels, where biomass and nutrient content of eelgrass were greater and where depletion from grazing was probably less. During higher low tides, Brant fed closer to previously visited grit sites. Tide cycles change over the course of the Brant's staging period on the bay, enabling longer and more frequent access to deeper eelgrass meadows as spring progresses. These seasonal changes in tidal pattern coincide with seasonal changes in Brant use of the bay. Thus, migration patterns for estuarine bird species might be shaped by latitudinal gradients in both food phenology and seasonal tidal patterns.
Nutritional Condition of Pacific Black Brant Wintering at the Extremes of Their Range
Authors: Mason Danielle D. , Barboza Perry S. , Ward David H. 
Published: September 2019

AbstractEndogenous stores of energy allow birds to survive periods of severe weather and food shortage during winter. We documented changes in lipid, protein, moisture, and ash in body tissues of adult female Pacific Black Brant (Branta bernicla nigricans) and modeled the energetic costs of wintering. Birds were collected at the extremes of their winter range, in Alaska and Baja California, Mexico. Body lipids decreased over winter for birds in Alaska but increased for those in Baja California. Conversely, body protein increased over winter for Brant in Alaska and remained stable for birds in Baja California. Lipid stores likely fuel migration for Brant wintering in Baja California and ensure winter survival for those in Alaska. Increases in body protein may support earlier reproduction for Brant in Alaska. Predicted energy demands were similar between sites during late winter but avenues of expenditure were different. Birds in Baja California spent more energy on lipid synthesis while those in Alaska incurred higher thermoregulatory costs. Estimated daily intake rates of eelgrass were similar between sites in early winter; however, feeding time was more constrained in Alaska because of high tides and short photoperiods. Despite differences in energetic costs and foraging time, Brant wintering at both sites appeared to be in good condition. We suggest that wintering in Alaska may be more advantageous than long-distance migration if winter survival is similar between sites and constraints on foraging time do not impair body condition.
Combining Breeding Bird Survey and Distance Sampling to Estimate Density of Migrant and Breeding Birds
Authors: Somershoe Scott G. , Twedt Daniel J. , Reid Bruce 
Published: September 2019

AbstractWe combined Breeding Bird Survey point count protocol and distance sampling to survey spring migrant and breeding birds in Vicksburg National Military Park on 33 days between March and June of 2003 and 2004. For 26 of 106 detected species, we used program DISTANCE to estimate detection probabilities and densities from 660 3-min point counts in which detections were recorded within four distance annuli. For most species, estimates of detection probability, and thereby density estimates, were improved through incorporation of the proportion of forest cover at point count locations as a covariate. Our results suggest Breeding Bird Surveys would benefit from the use of distance sampling and a quantitative characterization of habitat at point count locations. During spring migration, we estimated that the most common migrant species accounted for a population of 5000–9000 birds in Vicksburg National Military Park (636 ha). Species with average populations of >300 individuals during migration were: Blue-gray Gnatcatcher (Polioptila caerulea), Cedar Waxwing (Bombycilla cedrorum), White-eyed Vireo (Vireo griseus), Indigo Bunting (Passerina cyanea), and Ruby-crowned Kinglet (Regulus calendula). Of 56 species that bred in Vicksburg National Military Park, we estimated that the most common 18 species accounted for >8150 individuals. The six most abundant breeding species, Blue-gray Gnatcatcher, White-eyed Vireo, Summer Tanager (Piranga rubra), Northern Cardinal (Cardinalis cardinalis), Carolina Wren (Thryothorus ludovicianus), and Brown-headed Cowbird (Molothrus ater), accounted for >5800 individuals.
Monitoring Low Density Avian Populations: An Example Using Mountain Plovers
Authors: Dreitz Victoria J. , Lukacs Paul M. , Knopf Fritz L. 
Published: September 2019

Abstract
Declines in avian populations highlight a need for rigorous, broad-scale monitoring programs to document trends in avian populations that occur in low densities across expansive landscapes. Accounting for the spatial variation and variation in detection probability inherent to monitoring programs is thought to be effort-intensive and time-consuming. We determined the feasibility of the analytical method developed by Royle and Nichols (2003), which uses presence-absence (detection-nondetection) field data, to estimate abundance of Mountain Plovers (Charadrius montanus) per sampling unit in agricultural fields, grassland, and prairie dog habitat in eastern Colorado. Field methods were easy to implement and results suggest that the analytical method provides valuable insight into population patterning among habitats. Mountain Plover abundance was highest in prairie dog habitat, slightly lower in agricultural fields, and substantially lower in grassland. These results provided valuable insight to focus future research into Mountain Plover ecology and conservation.
Pattern of Damage to Albino Great Frigatebird Flight Feathers Supports Hypothesis of Abrasion by Airborne Particles
Authors: Schreiber Ralph W. , Schreiber Elizabeth A. , Peele Ashley M. , Burtt Edward H. 
Published: September 2019

Abstract
On 11 July 1985, an albino juvenile Great Frigatebird (Fregata minor) was collected by RWS and EAS on Christmas Island (2°N, 157°W) in the tropical Pacific. First observed on 13 July 1984 as a 55–60-day-old chick, the albino was seen flying about the colony on 4 November 1984 and again in February 1985. In July 1985 the juvenile was at its nest with such badly abraded plumage that it could not fly. Burtt (1986) proposed an aerodynamic model that predicts the distribution of melanic feathers in response to abrasion from airborne particles in a flying bird. The albino frigatebird provides a test of this model, since frigatebirds spend most of their time flying and rarely contact water, ground, or objects. Abrasion of the primaries and tail of this albino Great Frigatebird follows the pattern predicted by Burtt (1986). Furthermore, the pattern of damage to secondaries and tertiaries suggests that friction of feathers against each other is another important source of wear.
Distribution and Prevalence of Mosquito-Borne Diseases in O’ahu ’Elepaio
Authors: Vanderwerf Eric A. , Burt Matthew D. , Rohrer Joby L. , Mosher Stephen M. 
Published: September 2019

AbstractAbstractThe endemic Hawaiian avifauna is one of the most imperiled on earth, and diseases have been one of the most serious causes of species declines. From 1995–2005, we mist-netted and banded 266 endangered O’ahu ’Elepaio (Chasiempis sandwichensis ibidis) from 27 sites, examined them for visible symptoms of avian pox virus (Poxvirus avium), and screened blood samples for avian malaria (Plasmodium relictum). Pox-like lesions and malaria were found in all ’Elepaio populations on O’ahu; no parts of the island were free of these mosquito-borne diseases. Each year, 20% ± 4% of ’Elepaio had active lesions likely caused by pox and an additional 16% ± 4% had deformities and missing toes indicative of healed pox lesions. Prevalence of malaria was 87% over all years combined. Pox prevalence varied among years and was associated with annual rainfall, presumably due to greater abundance of mosquito breeding sites in wet years. Rainfall amounts at least as high as those associated with pox epizootics in 1996 and 2004 have occurred in 13 years since 1947, or once every 4.5 years. Severity of infection varied considerably among birds, and infections involving three or more toes, the feet, or the head were less common in birds with healed lesions than those with active lesions, suggesting such infections resulted in mortality more often. Disease resistance may be evolving in some areas, but ’Elepaio populations on O’ahu are likely to further decline.
Does Body Size Affect a Bird's Sensitivity to Patch Size and Landscape Structure?
Authors: Winter Maiken , Johnson Douglas H. , Shaffer Jill A. 
Published: September 2019

Abstract

Abstract
Larger birds are generally more strongly affected by habitat loss and fragmentation than are smaller ones because they require more resources and thus larger habitat patches. Consequently, conservation actions often favor the creation or protection of larger over smaller patches. However, in grassland systems the boundaries between a patch and the surrounding landscape, and thus the perceived size of a patch, can be indistinct. We investigated whether eight grassland bird species with different body sizes perceived variation in patch size and landscape structure in a consistent manner. Data were collected from surveys conducted in 44 patches of northern tallgrass prairie during 1998–2001. The response to patch size was very similar among species regardless of body size (density was little affected by patch size), except in the Greater Prairie-Chicken (Tympanuchus cupido), which showed a threshold effect and was not found in patches smaller than 140 ha. In landscapes containing 0%–30% woody vegetation, smaller species responded more negatively to increases in the percentage of woody vegetation than larger species, but above an apparent threshold of 30%, larger species were not detected. Further analyses revealed that the observed variation in responses to patch size and landscape structure among species was not solely due to body size per se, but to other differences among species. These results indicate that a stringent application of concepts requiring larger habitat patches for larger species appears to limit the number of grassland habitats that can be protected and may not always be the most effective conservation strategy.