bluuebunny/crossref_metadata_2025_split huggingface dataset:
Forest Edges Negatively Affect Golden-Cheeked Warbler Nest Survival
Authors: Peak Rebecca G. 
Published: September 2019

AbstractAbstract. I used an information-theoretic approach to determine support for hypotheses concerning the effects of edge and temporal factors on Golden-cheeked Warbler (Dendroica chrysoparia) nest survival on Fort Hood Military Reservation, Texas, during 2003–2006. I predicted that nest survival would be greater earlier in the breeding season than later in the breeding season, in areas with less forest edge than in areas with more forest edge, and during the laying and incubation stages than during the nestling stage. I used the logistic-exposure method to model nest survival as a function of the explanatory variables and to produce model-based estimates of daily and period survival. The overall daily survival rate was 0.96 (95% CI: 0.94, 0.97) and overall period survival was 0.34 (95% CI: 0.23, 0.46). Forest edge density had the strongest effect on nest survival. Nest survival decreased as forest edge density increased. Period survival tended to decrease as the breeding season progressed, but the 95% confidence intervals of the model-averaged parameter estimates overlapped. These results demonstrate that effective conservation strategies designed to provide high-quality breeding habitat for this endangered species should include measures to reduce predation by edge-adapted predators.
Environmental Correlates of Nesting Success in Red-Shouldered Hawks
Authors: Morrison Joan L. , McMILLIAN Michael , Cohen Jonathan B. , Catlin Daniel H. 
Published: September 2019

AbstractAbstract. We evaluated the influence of weather on reproduction of the Red-shouldered Hawk (Buteo lineatus) in an agricultural landscape in south-central Florida where we found relatively high densities of successfully nesting hawks. We used a generalized linear modeling approach within an information-theoretic framework to examine the influence of total rainfall, rainfall frequency, and temperature on the timing of nesting, nesting success, and productivity of hawks during 1995–2000. The best models indicated an influence of rainfall frequency and laying period on hawk reproduction. During years with less frequent rainfall in the summer and fall months prior to the beginning of the breeding season, fewer pairs attempted to nest, and hawks nested later and had smaller clutch sizes and lower productivity. Hawks that nested later in the breeding season had lower hatching success and lower overall nest success. Although Red-shouldered Hawks are generally reported to inhabit forested landscapes throughout their range, a common feature seems to be a dependence on wetlands and riparian habitat for foraging. We propose that the proportion of wetlands throughout the landscape is a unique aspect of south-central Florida that may allow for persistence of unusually high numbers of hawks.
Corticosterone Levels in Relation to Change of Mate in Black-Legged Kittiwakes
Authors: Angelier Frederic , Moe BØRGE , Clement-Chastel Celine , Bech Claus , Chastel Olivier 
Published: September 2019

Abstract
Abstract. In birds, changing mates generally results in decreased breeding success. Although costs and benefits of pair break-up have been well studied, endocrine mechanisms associated with mate change are poorly known. We measured baseline and stress-induced corticosterone levels in relation to mate change in Black-legged Kittiwakes (Rissa tridactyla). Baseline corticosterone levels were higher in kittiwakes breeding with a new mate than in kittiwakes that did not change mate. Stress-induced corticosterone levels were not influenced by change of mate. Elevated baseline corticosterone levels in birds breeding with a new mate could result from the social stress associated with pair break-up or mirror a higher energetic demand resulting from a lack of coordination between new pair members. Our results emphasize the usefulness of corticosterone levels in elucidating the effects of mate change on the energetic demands of reproduction in free-living birds.
Are Nestlings the Cue for Reduction of the Adrenocortical Response to Stress in Male Yellow Warblers Breeding at High Latitude?
Authors: Morgan Wilson C. , Holberton Rebecca L. 
Published: September 2019

AbstractAbstract. Acute corticosterone secretion helps individuals survive perturbation, particularly when faced with unpredictable conditions. However, elevated corticosterone is often incompatible with reproduction. Male Yellow Warblers (Dendroica petechia) breeding at high latitude avoid this conflict by exhibiting a reduced adrenocortical response while provisioning nestlings. To determine if this reduction is cued by nestlings, in June 2000 we switched clutches between nest pairs to manipulate hatching date. We sampled males with early-hatching clutches for the adrenocortical response 24 hr after nestlings hatched, but 24 hr prior to the premanipulated (original) hatching date. Similarly, we sampled males with late-hatching clutches 24 hr after the original hatching date, but prior to nestlings hatching. Males with early-hatching clutches (n  =  6) showed no reduced adrenocortical response, while males with late-hatching clutches (n  =  6) appeared to show a reduced response even without nestlings, suggesting that nestlings do not cue the reduction. An endogenous clock, day-counting mechanism, or hormonal changes may be associated with the reduced adrenocortical response.
Reproductive Biology of the Violet-Chested Hummingbird in Venezuela and Comparisons with Other Tropical and Temperate Hummingbirds
Authors: Fierro-Calderón Karolina , Martin Thomas E. 
Published: September 2019

AbstractAbstract. We provide details on the breeding biology of the Violet-chested Hummingbird (Sternoclyta cyanopectus) based on 67 nests studied in Yacambú National Park, Venezuela, from 2002 through 2006. Clutch size was two white eggs, usually laid every other day. Fresh egg mass (0.95 ± 0.14 g) was 15% of female mass. Incubation and nestling periods were 20.4 ± 0.3 and 26.0 ± 0.4 days, respectively. Nest attentiveness increased from 60% in early incubation to 68% in late incubation. The female spent 50% of her time brooding young nestlings, but ceased brooding by 13 days of age. Only the female fed the young, with a low rate of nest visitation (3.3 trips per hour) that did not increase with age of the young. Growth rate based on nestling mass (K  =  0.28) was slow. Daily predation rates decreased across stages and were 0.064 ± 0.044, 0.033 ± 0.008, and 0.020 ± 0.006 during the egg-laying, incubation, and nestling periods, respectively. Most, but not all, life history traits of the Violet-chested Hummingbird were similar to those reported for other tropical and temperate hummingbirds, providing further evidence that this family shows a relatively narrow range of life history variation.
Using Color to Define Species Boundaries: Quantitative Analysis in the Orchard Oriole Complex Supports the Recognition of two Species
Authors: Kiere Lynna M. , Hofmann Christopher M. , Tracy Ian E. , Cronin Thomas W. , Leips Jeff , Omland Kevin E. 
Published: September 2019

Abstract
Abstract. The recent divergence of Orchard (Icterus spurius spurius) and Fuertes's Orioles (I. s. fuertesi) makes them an ideal system for investigating species boundaries. Orchard and Fuertes's Orioles differ in several respects. They have distinct breeding ranges—Fuertes's Orioles breed in eastern coastal Mexico, whereas Orchard Orioles breed throughout eastern and central North America—and differ in plumage coloration, with adult male Orchard Orioles appearing “chestnut” and Fuertes's Orioles “ochre.” However, no detailed quantitative color analyses have been conducted. To characterize these differences we quantitatively measured plumage color using reflectance spectrometry. The colored plumages of adult male Orchard and Fuertes's Orioles have unique spectral characteristics, with no color overlap between them. Combined with life history differences and previous molecular studies, these findings support the classification of Orchard and Fuertes's Orioles as separate species. Additionally, this study demonstrates the utility of quantitative color measurement as a tool for examining species boundaries.
On the Allometric Relationship Between Size and Composition of Avian Eggs: A Reassessment
Authors: Arnold Todd W. , Green Andy J. 
Published: September 2019

AbstractAbstract. Numerous investigators have used allometric regression to characterize the relationship between proportional egg composition and egg size, which is a potentially important characterization for assessing maternal investment in reproduction. Herein, we document two important shortcomings of this approach. First, regressing log component mass against log egg mass involves regressing Y on itself, since each component (Y) is necessarily a part of the whole egg (X). This creates correlated errors, which leads to biased estimates of the regression slope. To circumvent this problem, we recommend regressing egg component masses on a relatively inert component like total water mass. Secondly, investigators routinely use ordinary least squares regression to estimate the slope of allometric relationships, which assumes that all error resides in Y. We demonstrate that this assumption is false, but so are the underlying error assumptions of commonly used alternatives such as reduced major axis and major axis regression. Because each egg is unique and determining composition involves destructive sampling, there is no obvious way to assess measurement error in Y versus X. As a solution, we recommend that investigators analyze multiple eggs per clutch whenever possible and fit a reduced major axis based on the among-female component of variability.
Home Range Attributes and Habitat Selection of Barred Owls and Spotted Owls in an Area of Sympatry
Authors: Hamer Thomas E. , Forsman Eric D. , Glenn Elizabeth M. 
Published: September 2019

AbstractWe compared home range areas and habitat selection of radio-marked Spotted Owls (Strix occidentalis) and Barred Owls (Strix varia) in an area of sympatry in the northern Cascade Range of Washington in 1986–1989. On average, home ranges of Spotted Owls were 3–4 times larger than ranges of Barred Owls, and there was little overlap of home ranges during the breeding season. Ranges of both species tended to expand during winter. Home range size of both species was negatively correlated with the amount of old forest, but the negative slope of the regression was much steeper for Spotted Owls than for Barred Owls. For both species, home ranges of individual owls typically had high overlap among seasons and years, indicating high site fidelity. Barred Owls generally occupied home ranges at lower elevations than Spotted Owls (mean  =  386 ± 27 m vs. 750 ± 68 m). Both species tended to use old forests more than expected, but Spotted Owls tended to use other cover types less than expected, whereas Barred Owls used most other cover types in proportion to their availability. We suggest that Spotted Owls may use larger ranges than Barred Owls because they prey selectively on a few species of nocturnal mammals, whereas Barred Owls forage more evenly across a broad range of prey types, including diurnal and aquatic species. The low overlap of Barred Owl and Spotted Owl home ranges suggests that territorial Barred Owls exclude Spotted Owls from their territories, at least during the breeding season, thus reducing the amount of habitat available to Spotted Owls.
Optimizing Nest Survival and Female Survival: Consequences of Nest Site Selection for Canada Geese
Authors: Miller David A. , Grand James B. , Fondell Thomas F. , Anthony R. MICHAEL 
Published: September 2019

AbstractWe examined the relationship between attributes of nest sites used by Canada Geese (Branta canadensis) in the Copper River Delta, Alaska, and patterns in nest and female survival. We aimed to determine whether nest site attributes related to nest and female survival differed and whether nest site attributes related to nest survival changed within and among years. Nest site attributes that we examined included vegetation at and surrounding the nest, as well as associations with other nesting birds. Optimal nest site characteristics were different depending on whether nest survival or female survival was examined. Prior to 25 May, the odds of daily survival for nests in tall shrubs and on islands were 2.92 and 2.26 times greater, respectively, than for nests in short shrub sites. Bald Eagles (Halieaeetus leucocephalus) are the major predator during the early breeding season and their behavior was likely important in determining this pattern. After 25 May, when eagle predation is limited due to the availability of alternative prey, no differences in nest survival among the nest site types were found. In addition, nest survival was positively related to the density of other Canada Goose nests near the nest site. Although the number of detected mortalities for females was relatively low, a clear pattern was found, with mortality three times more likely at nest sites dominated by high shrub density within 50 m than at open sites dominated by low shrub density. The negative relationship of nest concealment and adult survival is consistent with that found in other studies of ground-nesting birds. Physical barriers that limited access to nest sites by predators and sites that allowed for early detection of predators were important characteristics of nest site quality for Canada Geese and nest site quality shifted within seasons, likely as a result of shifting predator-prey interactions.
Survival of Postfledging Grassland Birds in Missouri
Authors: Suedkamp Wells Kimberly M. , Ryan Mark R. , Millspaugh Joshua J. , Thompson Frank R. , Hubbard Michael W. 
Published: September 2019

Abstract
We describe survival patterns during the postfledging period for two species of grassland birds in Missouri. We monitored 155 radio-marked juvenile Dickcissels (Spiza americana) and 107 juvenile Eastern Meadowlarks (Sturnella magna; hereafter meadowlark) in southwestern Missouri, from 2002 to 2004. We used an information theoretic approach to evaluate support for biological, temporal, and spatial covariates on survival estimates using Cox proportional hazards models, and also identified cause-specific mortality. For Dickcissels, the model with biological covariates containing body mass had the lowest score using Akaike's information criterion, corrected for small sample sizes (AICc) and almost twice the support of the second-best model. For meadowlarks, the null model had the lowest AICc score, but the second-best model containing body mass was also competitive (within 2 AICc units), so we used the latter model for inference. Hazard ratios indicated that a 1 g increase in body mass was associated with a 3% (Dickcissels) and 2% (meadowlarks) reduction in the risk of death. The cumulative probability of surviving the study period (Dickcissels, 58 days, meadowlarks, 72 days) was 0.56 (95% CI: 0.49–0.65) for Dickcissels and 0.63 (95% CI: 0.54–0.74) for meadowlarks. Predation was the largest source of cause-specific mortality for both species and responsible for 56% (Dickcissels) and 70% (meadowlarks) of deaths. Snakes were the numerically dominant predator of juvenile Dickcissels, but there was not a numerically dominant predator of juvenile meadowlarks. Our results emphasize the importance of body condition on postfledging survival. Future studies should consider estimating postfledging survival rates within species across systems to understand the potential impacts of different predator communities on juvenile survival.
Stopover Ecology and Habitat Selection of Juvenile Swainson's Thrushes During Fall Migration Along the Northern California Coast
Authors: Tietz James R. , Johnson Matthew D. 
Published: September 2019

AbstractWe investigated selection of stopover habitat by juvenile Swainson's Thrushes (Catharus ustulatus) during fall migration at a site along the northern California coast. The study site vegetation consisted mainly of coniferous forest (pine [Pinus] and spruce [Picea]), with interspersed patches of broadleaf forest (willow [Salix] and alder [Alnus]) in poorly drained swales. For 26 birds captured and radio-tracked in 2002 and 2003, the average minimum stopover duration was 8.9 ± 1.0 days. For 20 of these birds with a sufficient number of locations, the average home range size was 1.9 ± 0.3 ha. Thrushes showed no overall pattern of selection for forest type within the study area or for forest type used inside their home range. Fat and lean birds selected forest types similarly within the study area and their home ranges. However, locations occupied by lean birds had twice as much huckleberry (Vaccinium ovatum) shrub cover and were 1.3 times more concealed by vegetation than locations occupied by fat birds. There were 2.5 times more huckleberries at occupied than random locations, and locations occupied by lean birds had 2.1 times more berries overall than those frequented by fat birds. Fecal analyses confirmed that huckleberries were a commonly consumed food (70% of sampled thrushes), but also revealed that thrushes ate arthropods (87%) and wax myrtle (Myrica californica) bracteoles (43%). The overall lack of forest type selection coupled with differences between fat and lean birds in selection for cover and fruit abundance suggests that fat level may influence microsite selection.
Diet, Food Preferences, and Digestive Efficiency of the Grayish Saltator, a Partly Folivorous Passerine
Authors: Rodríguez-Ferraro Adriana , García-Amado M. Alexandra , Bosque Carlos 
Published: September 2019

AbstractWe studied the diet of the Grayish Saltator (Saltator coerulescens) during the rainy and dry seasons in the Venezuelan llanos and examined its food preferences, digesta retention time, rate of food intake, and digestive efficiency, in captivity. Grayish Saltators fed almost exclusively on plant tissues throughout the year. Fruits and leaves were the most commonly consumed items, comprising 36% and 28% of the diet, respectively, averaged over the entire year. In pairwise choice trials, saltators preferred fruits over leaves and flowers, and wild over cultivated leaves. In the laboratory, saltators displayed food-processing traits typical of frugivorous passerines. When feeding on a fruit (banana mash) diet, they had a fast rate of food passage (digesta mean retention time  =  54 ± 26 min) and a relatively low digestive efficiency (average metabolizable energy coefficient  =  0.59 ± 0.11), which was compensated for by high rates of food intake (1.4 times body mass). Mean retention time of a leaf-supplemented diet was slightly shorter (average  =  45 ± 17 min). Birds maintained or increased their body masses under laboratory conditions when fed on a fruit diet but did not when fed exclusively with leaves. Saltators spent very little time foraging, and the amount of time varied seasonally (5% and 17% of the time in the rainy and dry seasons, respectively). Most of their time (ca. 50%) was dedicated to resting. The morphology of the digestive tract of this species is similar to other frugivorous birds, but the inner edge of the maxilla is serrated. We found no evidence of cellulolytic activity in the Grayish Saltator's gut. Together, all of these characteristics indicate that Grayish Saltators are partial folivores that rely on a “skimming” strategy of food consumption.
Diet of the Cauca Guan: Exploitation of a Novel Food Source in Times of Scarcity
Authors: Muñoz Marcia C. , Londoño Gustavo A. , Rios Margarita M. , Kattan Gustavo H. 
Published: September 2019

AbstractAlthough exotic species may have a negative impact on native organisms, they can in some cases provide abundant resources. Use of these resources may have important implications for habitat use, movement, and space requirements of native animals, and ultimately for population dynamics. We describe the diet of a population of the narrowly endemic Cauca Guan (Penelope perspicax) in the Colombian Andes. This guan demonstrates plasticity in its eating habits, feeding on an exotic tree species during periods of food scarcity. Based on direct observations and analysis of fecal samples over a one-year cycle, we found that guans fed on 89 species of fruits but also included foliage, flowers, and invertebrates in their diets. Guans fed on fruit species in proportion to their availability but favored some species with high fruit production or prolonged fruiting. Fruit availability, measured both in numbers of species and biomass, varied throughout the year, with a low in September–December. During the period of low fruit availability, guans congregated in large numbers at a Chinese ash (Fraxinus chinensis) plantation, where they fed on young leaves in large quantities. Ash was planted at this site over 40 years ago as part of a reforestation program, and plantations are invaded by native vegetation. Guans are abundant at this site, and seasonal consumption of ash foliage, a concentrated and abundant food source, may have influenced local population dynamics.
Contaminants in Lesser Scaup Eggs and Blood from Yukon Flats National Wildlife Refuge, Alaska
Authors: Matz Angela C. , Rocque Deborah A. 
Published: September 2019

AbstractDocumented declines in Lesser Scaup (Aythya affinis) populations may be caused by several factors, including reduced reproductive success or survival from exposure to environmental contaminants during winter, migration, or breeding. We evaluated organochlorines and inorganic elements in Lesser Scaup blood (n  =  14) and eggs (n  =  10) from a breeding area in the relatively pristine Yukon Flats National Wildlife Refuge in interior Alaska. Most contaminants were not at concentrations of concern. Lead was detected in only four blood samples, with an average when detected (0.29 mg kg−1 wet weight [ww]) slightly above background levels (0.20 mg kg−1 ww). Our study area had little or no hunting, but since lead exposure is correlated with hunting pressure, lead should be evaluated in other Lesser Scaup breeding areas. Strontium in eggs (mean  =  10.90 mg kg−1 dry weight [dw]) was significantly negatively correlated with eggshell thickness. Eggshell thickness was also 18% lower than in museum specimens, a percentage associated with population declines in other species, and was not correlated with other contaminants. Few comparative data in the literature exist, but productivity in this breeding area was low (mean nest success  =  12%), so further research on the effects of strontium on productivity through the mechanism of eggshell thinning is needed. Most environmental contaminants are unlikely to be affecting Lesser Scaup populations breeding in interior Alaska, but lead and strontium should be studied further.
Selenium Accumulation in European Starlings Nesting in a Selenium-Contaminated Environment
Authors: Santolo Gary M. 
Published: September 2019

Abstract
I compared selenium (Se) levels in blood, liver, egg, and diet samples from European Starlings (Sturnus vulgaris) nesting at Kesterson Reservoir, Merced County, California and the surrounding area. Concentrations were highest in adult and nestling blood (8.3 and 5.5 µg g−1, respectively), nestling liver (7.5 µg g−1), and eggs (4.6 µg g−1) from nest boxes in interior parts of Kesterson compared to those from the perimeter (adult and nestling blood  =  4.0 and 1.4 µg g−1, respectively, nestling liver  =  4.7 µg g−1, eggs  =  2.8 µg g−1) and off-site (nestling blood  =  3.8 µg g−1, liver  =  4.3 µg g−1, egg  =  2.7 µg g−1). No hatching failure or embryo effects were observed. Although I found strong positive relationships in Se levels among tissues and eggs, variability of dietary exposure and differences in depuration rates across tissues confounds prediction of Se concentration. Nevertheless, I found blood Se to be a good indicator of dietary exposure that can be sampled nondestructively.