bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationship Between Aspen Heartwood Rot and the Location of Cavity Excavation by a Primary Cavity-Nester, the Red-Naped Sapsucker
Authors: Losin Neil , Floyd Chris H. , Schweitzer Todd E. , Keller Sarah J.
Published: September 2019

We investigated nest-hole excavation by the Red-naped Sapsucker (Syphrapicus nuchalis) in aspen (Populus tremuloides) woodlands in western Colorado. Sapsuckers excavate nest cavities primarily in aspens infected with a heartwood rot fungus (Phellinus tremulae), which softens the heartwood of infected trees. We assessed the interior condition of fungus-infected aspen trunks by extracting wood samples with an increment corer to determine whether sapsuckers chose nest-hole locations based on the extent of healthy sapwood remaining. Comparing fungus-infected trees with and without cavities, cavity-bearing trees had thinner healthy sapwood. The depth of healthy sapwood also varied with compass direction, being thinnest on the south sides of fungus-infected aspens. Cavity entrance orientations were significantly biased to the south-southeast, corresponding with the directional bias in heartwood rot. These results suggest that the depth of healthy sapwood, and hence excavation effort, may be important in determining nest hole location for the Red-naped Sapsucker.
Sex-Related Natal Dispersal of Pied Flycatchers: How Far Away From Home?
Authors: Chernetsov Nikita , Sokolov Leonid V. , Kosarev Vladislav , Leoke Dmitry , Markovets Mikhail , Tsvey Arseny , Shapoval Anatoly P.
Published: September 2019

Over four years, nestling Pied Flycatchers (Ficedula hypoleuca) were banded and recaptured in nest boxes at a 44 km long and 1–1.5 km wide study area along the Courish Spit on the southeast Baltic coast. The return rate for males was nearly twice as high as for females. Males settled significantly closer to their natal sites than predicted by the null model, which assumed that any nest box in the study area was selected at random. For females, the frequency distribution of natal dispersal distances was not significantly different from that predicted by the null model. The difference in average dispersal distance between the sexes was highly significant. Although some individuals settled within tens of kilometers, most male Pied Flycatchers settled within several kilometers of their natal sites. We suggest that even if females settle on average farther from their natal sites than males do, both sexes imprint on a relatively small (several kilometers in diameter) area during postfledging exploration, to which they return each spring.
A Small Suboscine-Like Passeriform Bird from the Early Oligocene of France
Authors: Mayr Gerald , Manegold Albrecht
Published: September 2019

We report the wing bones of a small passeriform bird from the early Oligocene of France, which are among the earliest fossil remains of Passeriformes in Europe. The specimen is clearly distinguished from oscines, to which all extant European passeriforms belong, and closely resembles suboscine passerines in presumably derived features. If future, more complete specimens support its assignment to the suboscines, it would be the earliest fossil record of this passeriform taxon. Together with other fossils from the early Oligocene of Germany, it indicates that nonoscine passerines colonized Europe before the arrival of oscines.
Two New Late Pleistocene Avifaunas From New Mexico
Authors: Brasso Rebecka L. , Emslie Steven D.
Published: September 2019

We report two new late Pleistocene avifaunas from New Mexico, recovered from Sandia Cave during archaeological excavations by F. Hibben in the 1930s and the nearby Marmot Cave excavated in 2000. The fossil assemblage from Sandia Cave consists of at least 30 taxa, including seven extralimital and two extinct species, Coragyps occidentalis (extinct vulture) and Ectopistes migratorius (Passenger Pigeon). The avifauna from Marmot Cave is limited to eight taxa shared with Sandia Cave. Two new records of Gymnogyps californianus (California Condor) are reported from these sites, as well as new records of Lagopus sp. (ptarmigan), Aegolius funereus (Boreal Owl), and Micrathene whitneyi (Elf Owl) from New Mexico. Two new radiocarbon dates on fossil G. californianus from Sandia and Marmot cave are reported at 10 795 ± 50 and 25 090 ± 220 14C years before present (B.P.), respectively. These collections provide further evidence for mixed avian communities in New Mexico during the late Pleistocene and are similar to other cave avifaunas of comparable age from the Great Basin and Rocky Mountain regions. The birds from Sandia Cave that are shared with other fossil avifaunas include species currently found in arctic tundra, boreal, and steppe habitats, as well as open, xeric communities. This collection provides additional evidence for widespread steppe-tundra, shrub, and subalpine forest environments at lower elevations of western North America during the late Pleistocene.
Lifetime Reproductive Success of Bald Eagles in Northern California
Authors: Jenkins J. Mark , Jackman Ronald E.
Published: September 2019

We studied the breeding success of resident Bald Eagles (Haliaeetus leucocephalus) over a 20-year period along the Pit River drainage in northern California. In 258 nesting attempts at 10 intensively studied nesting territories, 0.31 to 1.65 young were produced per year per occupied territory (mean  =  0.97), with average nesting success of 62%. Nineteen individually banded breeding adult Bald Eagles produced from zero to 36 young during their lifetimes, and birds remained on their territories for 1–16 years following capture as adults. We calculated a 90% annual survival rate for breeding adults from our sample of 19 birds, with longevity of one banded eagle at 22 years. Eagles that bred on a territory for a greater number of years did not produce a greater number of young annually on average than other breeding birds. Larger males, as evidenced by body mass at capture, produced significantly more young over their lifetimes than smaller males. This same relationship did not hold for females, however. Seven banded pairs of adults remained together on their territories for 3–15 years. Reproduction decreased significantly following replacement of a breeding adult on a territory, and this effect continued for 2–3 years following replacement.
Eastern Bluebirds Eject Brown-Headed Cowbird Eggs
Authors: Peer Brian D. , Hawkins Lyndon R. , Steinke Edwin P. , Bollinger Patricia Blair , Bollinger Eric K.
Published: September 2019

The relationship between the Brown-headed Cowbird (Molothrus ater) and its cavity-nesting hosts has received little attention because of the assumption that cowbirds rarely parasitize these hosts. We tested the Eastern Bluebird (Sialia sialis), a host that is sometimes heavily parasitized by cowbirds, for egg ejection behavior. Bluebirds ejected 65% of experimentally added cowbird eggs (n  =  20), but ejected no experimentally added conspecific eggs (n  =  66). This suggests that cowbird parasitism, not conspecific brood parasitism, is the selective pressure responsible for egg ejection in this species. This level of rejection may be conservative because bluebirds nest in dark cavities, which may make cowbird eggs difficult to detect by bluebirds.
Sage-Grouse and Indirect Interactions: Potential Implications of Coyote Control on Sage-Grouse Populations
Authors: Mezquida Eduardo T. , Slater Steven J. , Benkman Craig W.
Published: September 2019

Coyotes (Canis latrans) are lethally controlled throughout the range of Greater Sage-Grouse (Centrocercus urophasianus) and it has been suggested that such control may benefit sage-grouse. However, the perceived benefits of control are based on the direct effects of coyotes on sage-grouse and largely ignore potential indirect interactions. Here, we summarize some of the evidence for direct effects in a simplified food web including coyotes and sage-grouse. There is very little evidence to suggest that coyotes have much of a direct negative effect on sage-grouse, but there is considerable evidence supporting direct interactions that would lead to positive indirect effects between coyotes and sage-grouse. The three likely forms of positive indirect effects arise because coyotes reduce the potential negative effects resulting from mesopredator release and apparent and exploitative competition. Mesopredator release would adversely affect sage-grouse if a decrease in coyotes allowed an increase in foxes (especially Vulpes vulpes), badgers (Taxidea taxus), and Common Ravens (Corvus corax), mesopredators that prey on sage-grouse eggs and young. A decrease in coyotes is likely to allow jackrabbits (Lepus spp.) to increase, which would cause sage-grouse to suffer from apparent competition if Golden Eagles (Aquila chrysaetos), which are perhaps the most important predator of adult sage-grouse, then increase in response to the increase in jackrabbits. This increase in jackrabbits may also depress the availability of sagebrush (Artemisia spp.) and forbs, leading to an increase in exploitative competition with sage-grouse. For these reasons, we argue that intense and extended lethal coyote control is likely detrimental to sage-grouse conservation.
Does The Presence of Barred Owls Suppress the Calling Behavior of Spotted Owls?
Authors: Crozier Michelle L. , Seamans Mark E. , GutiÉRrez R. J. , Loschl Peter J. , Horn Robert B. , Sovern Stan G. , Forsman Eric D.
Published: September 2019

Barred Owls (Strix varia) have expanded their range throughout the ranges of Northern (Strix occidentalis caurina) and California Spotted Owls (S. o. occidentalis). Field observations have suggested that Barred Owls may be behaviorally dominant to Spotted Owls. Therefore, we conducted a test of behavioral dominance by assessing responsiveness of Spotted Owls to conspecific calls when they were in the simulated presence (i.e., imitation of Barred Owl vocalizations) of a Barred Owl. We hypothesized that Spotted Owls would be less likely to respond to conspecific calls in areas where Barred Owls were common. We used a binary 2 × 2 crossover experimental design to examine male Spotted Owl responses at 10 territories randomly selected within two study areas that differed in abundance of Barred Owls. We also conducted a quasi experiment at four study areas using response data from any Spotted Owl (male or female) detected following exposure to Barred Owl calls. We inferred from the crossover experiment that the simulated presence of a Barred Owl might negatively affect Spotted Owl responsiveness. Both subspecies of Spotted Owl responded less to Spotted Owl calls after exposure to Barred Owl calls, Northern Spotted Owls responded less frequently in areas having higher numbers of Barred Owls, and California Spotted Owls responded less frequently than Northern Spotted Owls overall.
Climate Change Effects on Neotropical Manakin Diversity Based on Ecological Niche Modeling
Authors: Anciães Marina , Peterson A. Townsend
Published: September 2019

Assessing the nature and magnitude of potentialeffects of climate change on populations isimportant to anticipating effects on speciesdiversity for conservation planning. We usedecological niche modeling to predict present andfuture distributions of 49 species of manakins(Pipridae) and allies. Predictions forpresent-day distributions were highly coincidentwith independent test data, suggesting goodpredictive ability. Assuming no dispersal,projections of potential distributions underfour scenarios of climate change predicted that20% of manakin species would likely goextinct from their current ranges, and thatdistributions would in general be reduced andfragmented, regardless of the area ofpresent-day potential distribution or rarity.Predicted changes in potential distributions,spatial configuration of suitable habitats, andgeographic position of species ranges were moredramatic for species inhabiting flatlands thanfor montane species. These results are anexample of how ecological niche modelingtechniques can anticipate the nature andmagnitude of changes in biodiversity in responseto climate change.
The Role of Food, Nest Predation, and Climate in Timing of Wrentit Reproductive Activities
Authors: Preston Kristine L. , Rotenberry John T.
Published: September 2019

Timing of breeding activities by birds hasimportant fitness consequences, as deciding when tonest can affect nest success. For three breedingseasons, we provided supplemental food to Wrentits(Chamaeafasciata) inhabitingsemiarid shrublands. We tested the effects of foodsupplementation on timing of initial egg laying,number of nests attempted, timing of fledging, andlength of the breeding season. We also evaluatedwhether Wrentits timed nest initiation to avoidperiods of greatest predation risk. Our study wasconducted during a period of high interannualvariation in precipitation. Supplemental food didnot advance laying date in Wrentits. During adrought, even Wrentits given supplemental fooddelayed nesting, initiated fewer nesting attempts,fledged young earlier, and reduced the length ofthe breeding season. In a year of average rainfall,supplemental food allowed pairs to continuerenesting late into the summer, after repeated nestlosses from predation. Wrentits did not timenesting to avoid periods of greatest predationrisk. In timing initial breeding, Wrentits appearedto be responding to climatic conditions and toindirect cues that predicted environmentalconditions later in the breeding season rather thanto food availability at the time of egg laying.
Sex and Nest Stage Differences in the Circadian Foraging Behaviors of Nesting Burrowing Owls
Authors: Poulin Ray G. , Todd L. Danielle
Published: September 2019

We used infrared cameras to accurately record the circadian provisioning behaviors of nesting Burrowing Owls (Athene cunicularia) in southern Saskatchewan, Canada. We monitored 19 nests over three years and recorded 4675 prey deliveries. We found a sex-based difference in foraging behavior: males hunted vertebrates during crepuscular periods, and females hunted insects during diurnal periods. Males delivered between 82% and 96% of all vertebrate prey depending on the stage of the nest. Males delivered at least 90% of all insects during early nest stages, after which females delivered an average of 76% of the insects. The rate of vertebrate deliveries increased from 1.3 to 7.7 per 24 hr as the summer progressed, and the number of insect deliveries increased from less than 1 to 18.6 per 24 hr. Vertebrates comprised 98%–99% of prey biomass delivered until females began delivering insects, but even then vertebrates still comprised 94% of prey biomass. Insects were consistently delivered at the highest rate during the day and vertebrates were consistently delivered at the highest rates during the dusk and dawn periods.
The Prelaying Interval of Emperor Geese on the Yukon-Kuskokwim Delta, Alaska
Authors: Hupp Jerry W. , Schmutz Joel A. , Ely Craig R.
Published: September 2019

We marked 136 female Emperor Geese(Chencanagica) in western Alaskawith VHF or satellite (PTT) transmittersfrom 1999 to 2003 to monitor their spring arrivaland nest initiation dates on the Yukon Delta, andto estimate prelaying interval lengths once at thenesting area. Ninety-two females with functionaltransmitters returned to the Yukon Delta in thespring after they were marked, and we located thenests of 35 of these individuals. Prelayingintervals were influenced by when snow melted inthe spring and individual arrival dates on theYukon Delta. The median prelaying interval was15 days (range  = 12–19 days) in a year when snowmelted relatively late, and 11 days(range  = 4–16 days) in two warmer yearswhen snow melted earlier. In years when snow meltedearlier, prelaying intervals of <12 daysfor 11 of 15 females suggested they initiated rapidfollicle development on spring staging areas. Theprelaying interval declined by approximately0.4 days and nest initiation date increasedapproximately 0.5 days for each day a femaledelayed her arrival. Thus, females that arrivedfirst on the Yukon Delta had prelaying intervals upto four days longer, yet they nested up to fivedays earlier, than females that arrived last. Theproximity of spring staging areas on the AlaskaPeninsula to nesting areas on the Yukon Delta mayenable Emperor Geese to alter timing of follicledevelopment depending on annual conditions, and toinvest nutrients acquired from both areas in eggsduring their formation. Plasticity in timing offollicle development is likely advantageous in avariable environment where melting of snow cover inthe spring can vary by 2–3 weeksannually.
Postovulatory Follicles in Mallards: Implications for Estimates of Breeding Propensity
Authors: Lindstrom Eric B. , Eichholz Michael W. , Eadie John M.
Published: September 2019

We evaluated the use of postovulatory follicles (POFs) up to 90 days postlaying to determine breeding propensity and clutch size in Mallards (Anas platyrhynchos). During 2002–2003, we examined ovaries from 48 postbreeding female Mallards (24 captive, wild-strain and 24 radio-marked, free-ranging) with known laying histories at periods ranging from 30 to 90 days postlaying. We found that POFs remained identifiable macroscopically (at 4.6–16× magnification) in all females (24 of 24) collected 30–60 days postlaying and in 79% (19 of 24) of females collected 61–90 days postlaying. Using microscopic examination (20–80× magnification), we found that ≥1 POFs remained identifiable in all cross-sectioned ovaries collected from females up to 90 days postlaying. We found a weak correlation between macroscopic POF counts and observed clutch size for females collected 30–60 days postlaying, but not for females collected 61–90 days postlaying. Blind tests using ovaries from known nonbreeding females confirmed that experienced, independent observers correctly distinguished breeding from nonbreeding females 100% of the time up to 60 days postlaying using macroscopic techniques and up to 90 days postlaying using microscopic techniques. These findings indicate that POFs provide a viable method to estimate breeding propensity in free-ranging Mallard populations and potentially other waterfowl species.
Obtaining Offspring Genetic Material: A New Method for Species With High Nest Predation Rates
Authors: Tori Wendy P. , Ryder Thomas B. , Durães Renata , Hidalgo José R. , Loiselle Bette A. , Blake John G.
Published: September 2019

Over the past decade, the field of moleculargenetics has revolutionized our understanding ofavian mating systems, by demonstrating that socialbonds might not accurately reflect parentagebecause of unknown levels of cryptic mating(e.g., extra-pair copulations). Use ofmolecular genetics tools for paternity analysisrequires genetic material from putative parents andnestlings. Unfortunately, high nest predation ratesoften preclude detailed genetic studies of tropicaltaxa. Here, we describe a nondestructive methodthat increases the efficiency of obtaining geneticmaterial from offspring for a group of tropicalpasserines (Pipridae). The method entailsreplacing eggs with plaster replicas, incubatingeggs artificially, and returning hatchlings totheir original nests for further development. Thismethod greatly improved our ability to sampleoffspring, as we collected genetic material from100% of manipulated nests, compared to52% of unmanipulated nests.
Red-Headed Woodpecker Nest-Site Selection and Reproduction in Mixed Ponderosa Pine and Aspen Woodland Following Fire
Authors: Vierling Kerri , Lentile Leigh
Published: September 2019

Red-headed Woodpecker (Melanerpeserythrocephalus) populationsare declining at a continental scale, yet little isknown about their nest-site selection and reproductionwithin burned forests. We measured reproductiveparameters and nest-site characteristics at 17Red-headed Woodpecker nests and 17 random sitesbetween 2001 and 2004 in the Black Hills, SouthDakota. The average date the first egg was laid was 17June, and the average clutch size was 5.4 ±0.4. The daily nest survival rate averaged 0.98(overall nest success  = 47%), and predation was the major cause ofnest failure. Red-headed Woodpecker nests occurredfarther from grassland edges in large diameter snagswithin severely burned quaking aspen(Populustremuloides) stands.High-severity fire within these aspen stands resultedin a combination of snag and understorycharacteristics that differed from the surroundingpine forest matrix. Interactions between cover typeand burn severity may have important ecologicalconsequences for Red-headed Woodpeckers in a mixedconifer forest.
An Experimental Test of Snake Skin Use to Deter Nest Predation
Authors: Medlin Elizabeth C. , Risch Thomas S.
Published: September 2019

Some bird species utilize snake skins as nesting material, possibly to decrease predation. We constructed 60 artificial nests simulating the nests of Great Crested Flycatchers (Myiarchus crinitus) in nest boxes to test the prediction that snake skins deter nest predators. Twenty of the boxes lacked rat snake (Elaphe obsoleta) skins (control), 20 had a single skin in the nest, and 20 had a skin in the nest and another displayed outside the box. Five of the control boxes were depredated (20%), while none of the experimental boxes were depredated. Our results supported our prediction that use of snake skins would deter mammalian predators, particularly the southern flying squirrel (Glaucomys volans). Although our results suggest a potential adaptive explanation for this behavior, our design did not allow us to address the degree of olfactory or visual detection by the squirrels, and left other potential explanations untested.
Extra-Pair Fertilizations in Sandhill Cranes Revealed Using Microsatellite DNA Markers
Authors: Hayes Matthew A. , Britten Hugh B. , Barzen Jeb A.
Published: September 2019

The presence of extra-pair fertilizations (EPF) in a dense breeding population of Sandhill Cranes (Grus canadensis) was examined using six microsatellite DNA markers. In this long-lived species that maintains long-term pair bonds, 4.4%–11% of 45 chicks were not genetically related to one social parent, and extra-pair chicks were present in 5.6%–22% of 18 family groups. Two confirmed extra-pair chicks were from different broods of the same pair that was socially bonded for a minimum of 12 years. The social male was rejected as the genetic father of both of these chicks. Three other potential cases of EPF (two cases in which the social male was rejected as the genetic parent, one in which the social female was rejected) could also have resulted from mate replacement prior to sampling. The range of EPF in this population of Sandhill Cranes is similar to that of other species with similar mating systems. In the confirmed cases of EPF, the female was able to increase her individual reproductive success without losing her territory.
Shorebird Abundance and Distribution on the Coastal Plain of the Arctic National Wildlife Refuge
Authors: Brown Stephen , Bart Jonathan , Lanctot Richard B , Johnson James A , Kendall Steve , Payer David , Johnson Jay
Published: September 2019

The coastal plain of the Arctic National Wildlife Refuge hosts seven species of migratory shorebirds listed as highly imperiled or high priority by the U.S. Shorebird Conservation Plan and five species listed as Birds of Conservation Concern by the U.S. Fish and Wildlife Service. During the first comprehensive shorebird survey of the 674 000 ha “1002 Area” on the coastal plain, we recorded 14 species of breeding shorebirds at 197 rapidly surveyed plots during June 2002 and 2004. We also estimated detection ratios with a double counting technique, using data collected at 37 intensively studied plots located on the North Slope of Alaska and northern Canada. We stratified the study area by major habitat types, including wetlands, moist areas, uplands, and riparian areas, using previously classified Landsat imagery. We developed population estimates with confidence limits by species, and estimated the total number of shorebirds in the study area to be 230 000 (95% CI: 104 000–363 000), which exceeds the biological criterion for classification as both a Western Hemisphere Shorebird Reserve Network Site of International Importance (100 000 birds) and a Ramsar Wetland of International Importance (20 000 birds), even when conservatively estimated. Species richness and the density of many species were highest in wetland or riparian habitats, which are clustered along the coast.
Is Selectively Harvested Forest an Ecological Trap for Olive-Sided Flycatchers?
Authors: Robertson Bruce A. , Hutto Richard L.
Published: September 2019

Disturbance-dependent species are assumed to benefit from forestry practices that mimic the appearance of postdisturbance landscapes. However, human activities that closely mimic the appearance but not the fundamental quality of natural habitats could attract animals to settle whether or not these habitats are suitable for their survival or reproduction. We examined habitat selection behavior and nest success of Olive-sided Flycatchers (Contopus cooperi) in a naturally occurring burned forest and an anthropogenically created habitat type—selectively harvested forest. Olive-sided Flycatcher density and nestling provisioning rates were greater in the selectively harvested landscape, whereas estimated nest success in selectively harvested forest was roughly half that found in naturally burned forest. Reduced nest success was probably a result of the relatively high abundance of nest predators found in the artificially disturbed forest. These results are consistent with the hypothesis that selectively harvested forest can act as an “ecological trap” by attracting Olive-sided Flycatchers to a relatively poor-quality habitat type. This highlights the importance of considering animal behavior in biodiversity conservation.
Sexual Size Dimorphism and Morphological Evidence Supporting the Recognition of two Subspecies in the Galápagos Dove
Authors: Santiago-Alarcon Diego , Parker Patricia G.
Published: September 2019

Sexual size dimorphism is a conspicuous trait of many wild bird species. Differences in body size between the sexes might reflect selective pressures and trade-offs to optimize performance. Here, we analyze the size dimorphism of the Galápagos Dove (Zenaida galapagoensis) using principal component and discriminant analyses with samples obtained from six islands: Santiago, Santa Fe, Santa Cruz, Española, Genovesa, and Wolf. We also reanalyze published morphological data but also including additional samples from Wolf Island to account for morphological differences among islands. Males were significantly larger than females. Discriminant analyses correctly classified 98% of males and 100% of females, and cross-validation of the model correctly classified 97% of males and 98% of females. We created two sexual size dimorphism indices using wing chord and tarsus as body-size surrogates. Significant differences were found in the sexual size dimorphism index for both measurements among islands. Significant differences in sexual size dimorphism among islands might indicate the role of different selective pressures acting on individual islands (e.g., competition, predation, resources, sexual selection), which might result in life history variation of the species among islands. For the first time, we provide significant morphological evidence supporting the classification of the Galápagos Dove into two subspecies: Z. g. galapagoensis and Z. g. exsul.
Effects of Nest Habitat, Food, and Parental Behavior on Shorebird Nest Success
Authors: Allen Smith Paul , Grant Gilchrist H , Smith James N.M
Published: September 2019

In environments such as arctic tundra, where bird densities are low and habitats are comparatively homogeneous, suitable nest sites likely are not limited. Under these conditions, reproductive success of birds may be determined by factors other than the habitat characteristics of nest sites. We studied the relative influence of nest habitat, food, nest distribution, and parental behavior on the reproductive success of tundra-breeding shorebirds at East Bay, Southampton Island, Nunavut, Canada. From 2000 to 2002, we monitored the nests of five species: Black-bellied Plover (Pluvialis squatarola), Semipalmated Plover (Charadrius semipalmatus), Ruddy Turnstone (Arenaria interpres), White-rumped Sandpiper (Calidris fuscicollis), and Red Phalarope (Phalaropus fulicarius). For each species, habitat differed between nest sites and random sites. In contrast, habitat differed between successful and failed nest sites only for White-rumped Sandpipers. Shorebirds did not prefer to nest in habitats where food was most abundant. Although nest success varied among species in all years, artificial nest experiments suggested that interspecific variation in predation rate was not related to habitat type. Instead, the marked interspecific variation in nest success may have been related to incubation behavior. Species taking fewer incubation recesses had higher nest success, although these results should be viewed as preliminary. The factor with the greatest interannual influence on nest success was fluctuating predation pressure, apparently related to the abundance of predators and lemmings.
Survival of Band-Tailed Manakins
Authors: Pearce-Higgins James W. , Brace Robin C. , Hornbuckle Jon
Published: September 2019

We modeled annual apparent survival of Band-tailed Manakins (Pipra fasciicauda) inhabiting a contiguous forest site and a 10.9 ha forest fragment in lowland Bolivia based on six years of capture-recapture data. There was significant age-related variation in apparent survival, but adult survival rates did not differ significantly with sex. Apparent survival rates of immature birds differed between the two locations, while adult survival rates did not. The most parsimonious model therefore estimated annual survival at 10% for immature birds in the contiguous forest site, 53% for immature birds in the forest fragment, 46% for adults in the first year after initial capture and 68% for adults in subsequent years. Forest fragmentation may have reduced immature dispersal, leading to inflated apparent survival rates in the forest fragment.
Impact of Hurricane Isabel on Bald Eagle Nests and Reproductive Performance in the Lower Chesapeake Bay
Authors: Watts Bryan D. , Byrd Mitchell A.
Published: September 2019

We evaluated the impact of Hurricane Isabel on nest loss and reproductive performance of Bald Eagles (Haliaeetus leucocephalus) in the lower Chesapeake Bay. Approximately 40% of Bald Eagle nest trees (n  =  527) were damaged and 127 nests were lost during the storm. Nest loss was significantly higher than in years prior to and after the storm. Only 46% of pairs that lost nests attempted to breed the following season, compared to 85% of pairs that did not lose nests. Of the pairs that made breeding attempts, only 69% of pairs that lost nests during the hurricane produced young compared to 83% of pairs that did not lose nests. Average brood size was also reduced for pairs that lost nests. The disparity in reproductive performance between the two groups narrowed in the second breeding season after the storm. Hurricane Isabel had a significant but short-lived impact on the Bald Eagle breeding population in the lower Chesapeake Bay.
Assessing the Development of Shorebird Eggs Using the Flotation Method: Species-Specific and Generalized Regression Models
Authors: Liebezeit Joseph R , Smith Paul A , Lanctot Richard B , Schekkerman Hans , Tulp Ingrid , Kendall Steve J , Tracy Diane M , Rodrigues Robert J , Meltofte Hans , Robinson Julie A , Gratto-Trevor Cheri , Mccaffery Brian J , Morse Julie , Zack Steve W
Published: September 2019

We modeled the relationship between egg flotation and age of a developing embryo for 24 species of shorebirds. For 21 species, we used regression analyses to estimate hatching date by modeling egg angle and float height, measured as continuous variables, against embryo age. For eggs early in incubation, we used linear regression analyses to predict hatching date from logit-transformed egg angles only. For late incubation, we used multiple regression analyses to predict hatching date from both egg angles and float heights. In 30 of 36 cases, these equations estimated hatching date to within four days of the true hatching date for each species. After controlling for incubation duration and egg size, flotation patterns did not differ between shorebirds grouped by mass (≥100 g or <100 g) or taxonomy (Scolopacidae versus Charadriidae). Flotation progressed more rapidly in species in which both adults incubate the clutch versus species in which only one adult incubates the clutch, although this did not affect prediction accuracy. We also pooled all continuous data and created a generalized regression equation that can be applied to all shorebird species. For the remaining three species, we estimated hatching date using five float categories. Estimates of hatching date using categorical data were, overall, less accurate than those generated using continuous data (by 3%–5% of a given incubation period). Our equations were less accurate than results reported in similar studies; data collected by multiple observers and at multiple sites, as well as low sample sizes for some species, likely increased measurement error. To minimize flotation method prediction error, we recommend sampling in early incubation, collecting both egg angle and float height data in late incubation, and developing site- and species-specific regression models where possible.
Effect of Diet Composition on Plasma Metabolite Profiles in a Migratory Songbird
Authors: Smith Susan B , McWILLIAMS Scott R , Guglielmo Christopher G
Published: September 2019

Plasma metabolites provide information about the physiological state and fuel use of birds, and have been used for predicting refueling rates of birds during migratory stopovers. However, little is known about the effect of diet on metabolite concentrations in small songbirds. We investigated the effect of dietary macronutrient composition on lipid and protein metabolites in captive White-throated Sparrows (Zonotrichia albicollis). Birds fed a high-protein, low-carbohydrate insect diet had lower plasma triglyceride concentrations and higher plasma B-hydroxybutyrate concentrations than birds fed a high-carbohydrate, low-protein grain diet during feeding. The insect-fed birds also had higher plasma uric acid concentrations than grain-fed birds and birds fed a low-protein, high-fat, and high-carbohydrate fruit diet. Diet did not significantly influence plasma concentrations of glycerol or nonesterified fatty acids. After subsequent overnight fasting, birds in all three diet groups had similar concentrations of lipid metabolites, but uric acid was marginally elevated in insect-fed birds. Given that dietary macronutrient composition affected certain plasma metabolite concentrations in sparrows, investigators should consider such diet effects when using these metabolites to estimate refueling rates of free-living migratory songbirds, particularly in species that exhibit dietary plasticity during migration.
Cutaneous Water Loss and Lipids of the Stratum Corneum in Dusky Antbirds, a Lowland Tropical Bird
Authors: Muñoz-Garcia Agustí , Williams Joseph B
Published: September 2019

The stratum corneum, the outer layer of the epidermis, consists of flattened cells embedded in a matrix of lipids, primarily cholesterol, free fatty acids, ceramides, and cerebrosides. The stratum corneum forms a barrier to water vapor diffusion through the skin. In birds, the skin limits excessive water loss at thermoneutral temperatures, but also serves as a vehicle for thermoregulation during episodes of heat stress. We measured total evaporative water loss, cutaneous water loss, and lipids in the stratum corneum in Dusky Antbirds (Cercomacra tyrannina), the first such measurements ever made for birds living in tropical rain forests. We predicted that these birds would have high rates of cutaneous water loss because of their need to thermoregulate rather than to conserve water. We found that Dusky Antbirds lose twice as much water through their skin as birds from temperate environments. We also hypothesized that the proportion of cerebrosides in the stratum corneum would increase relative to that of ceramides if Dusky Antbirds use their skin as a thermoregulatory organ. However, we found that Dusky Antbirds did not show different proportions of ceramides and cerebrosides in the stratum corneum than other species of birds. We also found that Dusky Antbirds had low amounts of free fatty acids in their stratum corneum. Overall, our data support the idea that the interactions of the lipids in the stratum corneum may play an important role in determining rates of water vapor diffusion through the skin.
Offspring Discrimination Without Recognition: California Towhee Responses to Chick Distress Calls
Authors: Benedict Lauryn
Published: September 2019

Accurate offspring discrimination improves parental fitness by ensuring appropriate parental investment. In colonial avian species, offspring discrimination is often mediated by recognition of individual offspring vocalizations, but spatially segregated species do not necessarily need sophisticated recognition abilities if parents can use alternative information to distinguish offspring from nonoffspring. I experimentally tested the hypothesis that territorial California Towhee (Pipilo crissalis) parents use a location-based decision rule, instead of true vocal recognition of offspring, when deciding whether to respond to chick distress calls. Accurate responses to offspring distress calls should be favored by natural selection because they can have large fitness benefits if parents succeed in chasing away potential nest predators. Responses to nonoffspring, in contrast, may be costly and should not be favored by natural selection. Towhee parents were presented with a series of three playback experiments in which I manipulated the identity of the vocalizing chick, the age of resident chicks, and the location of the distress call broadcast. Parents showed no evidence of individual vocal recognition and no pattern of differential response to distress calls when offspring age differed from that of the calling chick. Parents did, however, exhibit a significant tendency to approach distress calls originating near their offspring more often than distress calls originating elsewhere on their territory. These results provide support for the evolution of an offspring discrimination strategy based on a simple location-based decision rule instead of true vocal recognition.
Nest Densities of Cavity-Nesting Birds in Relation to Postfire Salvage Logging and Time Since Wildfire
Authors: Saab Victoria A. , Russell Robin E. , Dudley Jonathan G.
Published: September 2019

We monitored the nest densities and nest survival of seven cavity-nesting bird species, including four open-space foragers (American Kestrel [Falco sparverius], Lewis's Woodpecker [Melanerpes lewis], Western Bluebird [Sialia mexicana], and Mountain Bluebird [S. currucoides]) and three wood-foragers (Hairy Woodpecker [Picoides villosus], Black-backed Woodpecker [P. arcticus], and Northern Flicker [Colaptes auratus]), after two wildfires (one partially salvage-logged and one unlogged) in western Idaho from 1994–2004. We estimated the relationship between nest density and time since fire, tested for statistical differences in nest densities and nest survival in the partially salvage-logged vs. unlogged wildfires, and tested for differences in nest survival between early (1–4 years after fire) and late (5–12 years after fire) postfire periods. Nest densities of open-space foragers and Northern Flickers generally increased with time since fire, whereas nest densities of Black-backed and Hairy Woodpeckers peaked 4–5 years postfire. Nest densities of wood-foraging species and Mountain Bluebirds were significantly higher in the unlogged burn, whereas Lewis's Woodpeckers had significantly higher nest densities in the partially logged burn. Kestrels tended to favor the partially logged burn, while Western Bluebird nest densities were nearly equal in both burned areas. For most species, postfire period and treatment (partially logged vs. unlogged) had little influence on nest survival. However, Hairy Woodpecker nest survival was significantly lower in the partially logged burn versus the unlogged wildfire in the early postfire period, and Lewis's Woodpecker nest survival was significantly reduced in the later postfire period versus the early postfire period in the partially logged burn. Importantly, the salvage logging was designed to retain more than half of the snags over 23 cm in diameter, which provided suitable nesting habitat for open-space foragers during the decade following fire.
Mercury and Stable Isotopes in Feathers Of Audouin's Gulls as Indicators of Feeding Habits and Migratory Connectivity
Authors: Sanpera Carola , Ruiz Xavier , Moreno Rocío , Jover Lluís , Waldron Susan
Published: September 2019

To better understand migratory connectivity between breeding and nonbreeding populations, we analyzed mercury (Hg) and stable isotope signatures of nitrogen (δ15N), carbon (δ13C), and sulfur (δ34S) in Audouin's Gulls (Larus audouinii) breeding in two different colonies, the Ebro Delta (northeastern Spain) and the Chafarinas Islands (southwestern Mediterranean). Although abundant information is available on the biology and trophic ecology of this gull's breeding populations, little is known about migration patterns, distribution in winter, or conditions faced during the nonbreeding period. Analyses were carried out on first primary feathers, grown during the summer while gulls are on the breeding grounds, and mantle feathers, grown during the winter. Different isotopic signatures (δ15N, δ13C, and δ34S) in summer (primary) feathers from each area agree with the observed differences in diet between the two colonies. In winter (mantle) feathers, isotopic signatures did not differ, consistent with a common wintering ground and common diet, although the lack of isotopic basemaps in marine systems precludes assignment to a geographical area of reference. Future research is needed to relate isotopic signatures and Hg values in mantle feathers to trophic ecology in wintering areas. Results for Hg indicate that the excretory role played by primary feathers precludes their use as indicators of trophic ecology.
Sexual Dimorphism and Parental Roles in the Thorn-Tailed Rayadito (Furnariidae)
Authors: Moreno Juan , Merino Santiago , Lobato Elisa , Rodríguez-Gironés Miguel A. , VÁSQUEZ Rodrigo A.
Published: September 2019

Sexual dimorphism, mating system, and parental care are known for only a few species of the large passerine family Furnariidae. We conducted a study of sexual dimorphism in morphology, coloration, and parental roles during incubation and chick-rearing in the Thorn-tailed Rayadito (Aphrastura spinicauda), a characteristic resident ovenbird of the southern temperate rainforests of Chile and Argentina. Through molecular sexing, morphological measurements, and spectrophotometric analysis of body plumage and rectrices of reproductive adults captured on Chiloé Island (southern Chile), we determined that males were between 2% and 10% larger than females in mass, tarsus length, and wing length, while no difference was found for the length of the bill or the two longest central rectrices and their characteristic spines, or in plumage coloration. Heavy males were paired with heavy females and light males with light females. Males and females participated equally in all reproductive activities during the incubation and nestling phases, except removal of nestling feces, in which females were twice as active as males. In a study of habitat use on Navarino Island (extreme southern Chile) we found that the extended graduated tail, with rectrices that end in spines, which gives the species its name, was not used as a support while foraging and could be related to another function such as sexual or social signaling. The absence of sexual dimorphism in plumage and parental roles in rayaditos may be related to the use of the long, graduated tail as a signal of quality by both sexes, although this hypothesis requires confirmation through future mate choice studies.
Disappearance of Breeding Semipalmated Sandpipers from Churchill, Manitoba: More than a Local Phenomenon
Authors: Jehl Joseph R.
Published: September 2019

As late as the 1940s the Semipalmated Sandpiper (Calidris pusilla) was the most abundant sandpiper breeding at Churchill, Manitoba. By the 1960s it had undergone a sharp decline, and by the mid-1990s the local population consisted of 11 pairs in a single colony. Nesting was last documented in 2001. Declines had also become evident at several other breeding sites along the Hudson Bay coast of Manitoba and Ontario, as well as in the number of migrants detected on the Atlantic coast of Canada and the northern United States. Information on the biology of the Churchill population in 1993–2004 largely agreed with that gathered at La Pérouse Bay, Manitoba, in the 1980s: reproductive success was good and new birds continued to join the colony; however, the number of breeding attempts by individuals was low and decreasing. As there is no evidence that the decline was related to local factors (e.g., altered habitats, climate change), it is probably attributable to mortality in the nonbreeding season, which leaves fewer birds available to return north. Whether causality can be fully resolved is problematic. Monitoring migrants can reveal population trends and studies on the breeding grounds can help frame hypotheses, but both approaches are time-consuming and provide only partial answers. In such cases, restoration of declining species may be best served by fostering habitat conservation throughout a species' range.
Geographic Variation in Contact Calls of Feral North American Populations of the Monk Parakeet
Authors: Buhrman-Deever Susannah C. , Rappaport Amy R. , Bradbury Jack W.
Published: September 2019

Introduced feral populations offer a unique opportunity to study the effects of social interaction and founder effects on the development of geographic variation in learned vocalizations. Introduced populations of Monk Parakeets (Myiopsitta monachus) have been growing in number since the 1970s, with a mixture of isolated and potentially interacting populations. We surveyed diversity in contact calls of Monk Parakeet populations in Connecticut, Texas, Florida, and Louisiana. Contact call structure differed significantly among the isolated populations in each state. Contact call structure also differed significantly among potentially interacting nest colonies in coastal Connecticut, and these differences did not follow a geographic gradient. Limited dispersal distances, founder effects, and social learning preferences may play a role in call structure differences.
Behavior and Phylogenetic Position of Premnoplex Barbtails (Furnariidae)
Authors: Ignacio Areta Juan
Published: September 2019

The Margarornis assemblage includes four genera: Margarornis, Premnoplex, Premnornis, and Roraimia, all thought to be closely related. Differences in vocalizations and habitat use between Premnoplex brunnescens (Spotted Barbtail) and P. tatei (White-throated Barbtail) are consistent with their full species status. In light of the weak anatomical (hindlimb musculature) evidence supporting the inclusion of Premnornis in the Margarornis assemblage, the convergence-prone nature of characters associated with climbing habits, and the differences in their nests and foraging behavior, I propose that Premnornis is not a member of the Margarornis assemblage and that Premnoplex is closely related only to Margarornis. These results are supported by recent molecular phylogenetic analyses. Although Roraimia differs in plumage, tail shape, and song from other members of the Margarornis assemblage, it must be provisionally included in the assemblage until evidence clarifies its phylogenetic position.