bluuebunny/crossref_metadata_2025 huggingface dataset:
Using Satellite Imagery to Model Distribution and Abundance Of Bicknell's Thrush (Catharus Bicknelli) in New Hampshire's White Mountains
Authors: Hale Stephen R.
Published: September 2019

Satellite imagery was used to model the distribution and abundance of Bicknell's Thrush (Catharus bicknelli) in the White Mountains of New Hampshire. Image-derived data for live softwood shrub density, standing dead-tree basal area, distance to nearest fir-shrub cover type, along with a digital elevation model and point-count data, were used to supply regressor estimates in a multivariate logistic habitat model that was constructed from field vegetation sampling and point-count data. Spatially explicit predictions of probability of Bicknell's Thrush presence were made for each 28.5 × 28.5 m-pixel covering 70,000 ha. A model validation procedure using observations independent from model calibration revealed no difference (P > 0.05) between modeled and observed estimates of Bicknell's Thrush presence within probability deciles 0 to <0.1, 0.1 to <0.2, 0.2 to <0.3, 0.3 to <0.4, 0.5 to <0.6, and 0.6 to <0.7 with respective densities (40 ha−1) of 0.5, 1.6, 2.8, 4.1, 7.3, and 9.4. Transforming probabilities into relative abundance produced an estimated 4,900 Bicknell's Thrushes across the study area. Habitats supporting the highest density of Bicknell's Thrushes were predicted to be at the uppermost elevations. However, abundance estimates decreased even as density increased, owing to decreasing amounts of habitat area with increasing elevation, and suggested that lower-elevation, low-density habitats may support a significant fraction of Bicknell's Thrushes.

Utilisation de l'Imagerie Satellitaire afin de Modéliser la Distribution et l'Abondance de Catharus bicknelli dans les White Mountains du New Hampshire
Seasonal Migration, Speciation, and Morphological Convergence in the Genus Catharus (Turdidae)
Authors: Winker Kevin , Pruett Christin L.
Published: September 2019

The effects of seasonal migration on evolutionary change within lineages is poorly understood, in terms of both differentiation (cladogenesis) and specialization (anagenesis). Regarding differentiation, two contradictory hypotheses exist: Seasonal migration counters differentiation; or it can stimulate differentiation by exposing lineages to new environments. Regarding specialization, the morphological consequences of a migratory life history have not been well explored. We examined these issues by reconstructing morphological and molecular phylogenies of the genus Catharus (Turdidae), a group of forest-dwelling, New World thrushes traditionally considered to include a small “species flock” of Nearctic-Neotropic migrants. DNA sequence data (2,920–3,027 base pairs) do not support traditional taxonomy, and morphological characters conflicted with these data. Results suggest that long-distance seasonal migration arose independently four times in Catharus sensu lato (including Hylocichla mustelina). Correlated morphological evolution occurred among several characters in these lineages, and these shared traits may stem from ecological conditions in Nearctic forests.

Migración Estacional, Especiación y Convergencia Morfológica en el Género Catharus (Turdidae)
Fat Affects Predator-Avoidance Behavior in Gray Catbirds (Dumetella Carolinensis) During Migratory Stopover
Authors: Cimprich David A. , Moore Frank R.
Published: September 2019

During migration, birds may store large quantities of fat to fuel long-distance flight. Because mass affects flight performance, fat migrants should behave with greater caution toward aerial predators than lean migrants. We tested a prediction of this hypothesis, namely, that fat birds will remain motionless longer than lean birds after a simulated encounter with a raptor. We captured Gray Catbirds (Dumetella carolinensis) during fall migration, classified their subcutaneous fat, exposed them to a model hawk, and then recorded the time until their first perch change. To determine whether the birds treated the simulated predator as a threat, we also tested them with a hexagon-shaped model and with no model. The birds remained motionless longer with the hawk model than either of the two other treatments. Fat birds remained motionless longer than lean birds when exposed to the hawk model, but we detected no difference with the other two treatments. These results provide evidence that fat affects the predator-avoidance behavior of Gray Catbirds during migratory stopover. That a difference between fat and lean groups was only apparent with the hawk model treatment suggests that the result is attributable to differences in the flight performance of the two groups rather than simply a difference in motivation to begin foraging. We suggest that fat should influence the behavior of a wide variety of migrant birds, particularly those species that typically carry greater fat reserves or that forage in more exposed situations than the Gray Catbirds we tested.

La Grasa Afecta el Comportamiento de Evasión de Depredadores en Dumetella carolinensis durante las Paradas Migratorias
Gosling Growth and Survival in Relation to Brood Movements in Greater Snow Geese (Chen Caerulescens Atlantica)
Authors: Mainguy Julien , Gauthier Gilles , Giroux Jean-François , Bêty Joël
Published: September 2019

Post-hatch brood movements to high-quality foraging sites are common in precocial birds but may entail costs for young. We assessed effects of overland movements of broods between the nesting and rearing areas in Greater Snow Geese (Chen caerulescens atlantica) breeding on Bylot Island, Nunavut, Canada, to determine whether these movements affected gosling survival and growth. We monitored 51 radiomarked females over five years to quantify movement distance, movement duration, and gosling survival. Gosling growth was compared over four years using a sample of web-tagged broods recaptured shortly before fledging among adults that (1) nested and reared their young in a dense colony, (2) left the colony and moved ≈30 km to reach the main brood-rearing area, or (3) nested and reared their young in the main brood-rearing area. Brood movements by radio-marked birds were highly variable (2.6-52.5 km, depending on rearing areas used) and fairly rapid (≤6 days after hatch for 72% of the females). Gosling survival was not related to distance moved between nesting and brood-rearing areas. However, gosling growth was influenced by areas used and whether or not they had to move to reach their brood-rearing area. Geese nesting at the main brood-rearing area generally reared heavier and larger goslings than those that moved ≈30 km from the main nesting colony to rear their brood at the main brood-rearing area. On the other hand, goslings leaving the nesting colony after hatch were heavier and larger than those that stayed there throughout brood rearing in one of two years. Although brood movements allow goslings access to high-quality habitats, they entail some costs. Thus, minimizing such movements through nest-site selection should provide a selective advantage by allowing goslings to maximize their growth.

Croissance et Survie des Oisons en Relation avec les Déplacements des Familles chez Chen caerulescens atlantica
Sex-Related Natal Dispersal of White Storks (Ciconia Ciconia) in Poland: How Far and Where to?
Authors: Chernetsov Nikita , Chromik Wiesław , Dolata Pawel T. , Profus Piotr , Tryjanowski Piotr
Published: September 2019

Distance and direction of natal dispersal were studied in a Polish White Stork (Ciconia ciconia) population on the basis of 25 years of banding and resighting data. Multiple regression analysis showed a significant sex-linked bias (females settled farther from the natal sites than males) and effect of banding year, in that dispersal distances were decreasing toward the end of the study period. Population indices in the hatching year and the presumed recruitment year did not help to explain the variance. The birds showed a trend toward settling southeast of the natal site, but this was significant only in individuals that settled within 50 km of the natal site. We suggest that when returning from winter sites in the southeast, young White Storks settle before they reach their presumed migratory target in the vicinity of the natal site. This is only possible if, in spite of a relatively high population density, many breeding areas and potential nesting sites remain vacant. This might also explain our failure to find density dependence in the interannual variation of dispersal distances.
Associations of Breeding Birds With Fire-Influenced and Riparian-Upland Gradients in a Longleaf Pine Ecosystem
Authors: Allen Jennifer C. , Krieger Sharlene M. , Walters Jeffrey R. , Collazo Jaime A.
Published: September 2019

We determined the effects of fire history and a riparian-upland gradient on the breeding bird community at Fort Bragg Military Installation in North Carolina, one of the largest remnant areas of the endangered longleaf pine (Pinus palustris) ecosystem. Study sites were classified into two treatments: fire-intense (areas experiencing growing-season burns) and fire-suppressed (areas lacking fires). Within each treatment, bird and vegetation data were recorded at point-count stations positioned at three distances from streamhead pocosins to characterize the riparian-upland habitat gradient: 0, 75, and ≥150 m. Total bird abundance and species richness varied significantly along the riparian-upland gradient, with pocosins contributing greatly to avian biodiversity. Our data revealed strong effects of fire history and riparian-upland gradient on bird species, which we described in terms of breeding-bird assemblages. Members of the open longleaf assemblage (e.g., Red- cockaded Woodpecker [Picoides borealis], Bachman's Sparrow [Aimophila aestivalis]) were most common in fire-intense areas and at upland locations. Members of the fire-suppressed assemblage (e.g., Wood Thrush [Hylocichla mustelina], Ovenbird [Seiurus aurocapilla]) were confined to pocosins in fire-intense areas, but became more abundant in fire-suppressed areas. Members of the pocosin assemblage (e.g., Eastern Towhee [Pipilo erythropthalamus], Common Yellowthroat [Geothlypis trichas]) were largely confined to pocosins and, in some cases, were most abundant in fire-intense pocosins. Fire suppression increased structural diversity of vegetation and promoted one breeding-bird assemblage (fire-suppressed), but at the expense of two others (open longleaf, pocosin). Continued management of Fort Bragg to promote longleaf pine restoration is essential for supporting conservation of the open-longleaf bird assemblage; in addition, it will benefit the pocosin assemblage.

Asociaciones de Aves Reproductivas con Áreas Influenciadas por el Fuego y con Gradientes Ribereños-Tierras Altas en un Ecosistema de Pinus palustris
Carotenoids, Immunity, and Integumentary Coloration in Red Junglefowl (Gallus Gallus)
Authors: McGraw Kevin J. , Klasing Kirk C.
Published: September 2019

There is widespread interest in the roles that carotenoids play as yolk and shank pigments, antioxidants, and immune-system regulators in chickens, but nothing is known of such functions in the wild ancestors of chickens—the Red Junglefowl (Gallus gallus). We manipulated carotenoid access in the diet of captive male and female Red Junglefowl to investigate its effects on the coloration of the red comb and buff-brown legs and beak as well as on several indices of immunocompetence. Comb, leg, and beak did not differ in coloration between control and carotenoid-supplemented groups; in fact, biochemical analyses showed that, unlike in chickens, leg and beak tissue contained no carotenoids. Carotenoids showed variable effects on immunological performance, boosting the potency of whole blood in males to kill bacterial colonies, while inhibiting the ability of macrophages to phagocytize bacterial cells and having no significant effect on the accumulation of haptoglobin—an acute-phase protein whose production was induced by a simulated infectious challenge with lipopolysaccharide. These results bring into question interpretations of the evolutionary significance of carotenoid-based and sexually dichromatic shank coloration in domestic chickens, which was apparently derived through artificial selection, and suggest that carotenoids can exert different, mechanism-specific actions on the many lines of immune defense in birds.

Carotenoides, Inmunidad y Coloración Integumentaria en Gallus gallus
Estimating Detection Probabilities From Multiple-Observer Point Counts
Authors: Alldredge Mathew W. , Pollock Kenneth H. , Simons Theodore R.
Published: September 2019

Point counts are commonly used to obtain indices of bird population abundance. We present an independent-observer point-count method, a generalization of the dependent-observer approach, based on closed-population capture- recapture methods. The approach can incorporate individual covariates, such as detection distance, to account for individual differences in detection probabilities associated with measurable sources of variation. We demonstrate a negative bias in two-observer estimates by comparing abundance estimates from two- and four- observer point counts. Models incorporating data from four independent observers were capable of accounting for this bias. Modeling individual bird differences in detection probabilities produced abundance estimates 15–21% higher than models that did not account for individual differences, in four out of five data sets analyzed. Although independent-observer methods are expensive and impractical for large- scale applications, we believe they can provide important insights into the sources and degree of perception bias (i.e., probability of detecting an individual, given that it is available for detection) in avian point-count estimates. Therefore, they may be useful in a two-stage sampling framework to calibrate larger surveys based on single-observer estimates.

Estimación de Probabilidades de Detección a Partir de Conteos en Puntos Hechos por Varios Observadores
Avian Flight
Authors: Dial Ken
Published: September 2019

The following critiques express the opinions of the individual evaluators regarding the strengths, weaknesses, and value of the books they review. As such, the appraisals are subjective assessments and do not necessarily reflect the opinions of the editors or any official policy of the American Ornithologists' Union.
Nesting Birds of a Tropical Frontier: The Lower Rio Grande Valley of Texas
Authors: Woodin Marc C.
Published: September 2019

The following critiques express the opinions of the individual evaluators regarding the strengths, weaknesses, and value of the books they review. As such, the appraisals are subjective assessments and do not necessarily reflect the opinions of the editors or any official policy of the American Ornithologists' Union.
Wildlife Demography: Analysis of Sex, Age, and Count Data
Authors: Conroy Michael J.
Published: September 2019

The following critiques express the opinions of the individual evaluators regarding the strengths, weaknesses, and value of the books they review. As such, the appraisals are subjective assessments and do not necessarily reflect the opinions of the editors or any official policy of the American Ornithologists' Union.
Importance of Facial Pattern to Sexual Selection in Golden-Winged Warbler (Vermivora Chrysoptera)
Authors: Leichty Ellen R. , Grier James W.
Published: September 2019

The importance of the black facial pattern in sexual selection in Golden-winged Warblers (Vermivora chrysoptera) was evaluated through experimental plumage modification. We lightened the throat patch and eye mask with hair bleach, which essentially created artificial Brewster's Warbler (F1 generation of Golden-winged Warbler × Blue-winged Warbler [V. pinus]) plumage phenotypes. Experimental males lost their original territories and failed to obtain mates. We concluded that there is sexual selection against the Brewster's facial pattern. Sexual selection attributable to the face pattern may explain the apparent greater effect of hybridization on Golden-winged Warblers than on Blue-winged Warblers.

Importancia del Patrón Facial en la Selección Sexual de Vermivora chrysoptera
Courtship Ethology of Carola's Parotia (Parotia Carolae)
Authors: Scholes Edwin
Published: September 2019

Detailed descriptions of behavior patterns are a major objective of ethology, because they serve as the basis for identifying the elements that constitute the behavioral component of the phenotype. In regard to avian courtship displays, the lack of detailed studies has limited the scope of modern ethological investigations. Recent advances in video technology have greatly improved the ability to analyze complex avian behaviors. I examined the ethology of courtship and mating in Carola's Parotia (Parotia carolae) using a modern approach intended to facilitate incorporation into existing bioinformatics databases. The questions addressed are as follows. (1) What are the courtship and mating behaviors of wild Carola's Parotias? (2) How are these behaviors structured? And (3) what are the units that constitute complex patterns of behavior? I used digital video to thoroughly characterize two wild populations of Carola's Parotias in Papua New Guinea. The results present a detailed picture of the species' complex courtship ethology, including description of 20 behaviors and the lower-level structure (or “anatomy”) of male displays, which alone comprise 58 distinct elements. The modular nature of displays is demonstrated through instances in which various units and subunits are used recurrently, differentially employed, and added or deleted.

Etología del Cortejo en Parotia carolae
Singing Complexity of The Banded Wren (Thryothorus Pleurostictus): Do Switching Rate and Song-Type Diversity Send Different Messages?
Authors: Molles Laura E.
Published: September 2019

Most species of songbird possess repertoires of song types or variations that allow singers to vary how they present their songs. “Complexity,” or the amount of variation in a singing performance, has several distinct components that include the number of song types used, variation within song types, and rate of switching between song types. Because singers can control each factor somewhat independently, different components may encode different kinds of information. In a series of interactive playbacks, I presented Banded Wrens (Thryothorus pleurostictus) with stimuli that altered song-type diversity and switching rates independently. My results show that switching rates affect males' aggressive approach responses, with lower switching rates eliciting stronger responses. By contrast, song-type diversity does not appear to affect males' approach responses when switching rates are held at a high and constant level. Although focal male switching rates and song-type diversity are not strongly influenced by playback type, males frequently respond to high-diversity playback with delayed matches. Delayed matching entails using one or more of the same song types from the playback, without immediate song- type matching. Although delayed matches occurred at levels above chance during high-diversity playbacks, focal males appeared to avoid them during other types of playback; immediate matches were rare and repertoire matches frequent for all playback treatments. Overall, males' responses to the three playback stimuli suggest that switching rate and song-type diversity encode different messages.

Complejidad del Canto de Thryothorus pleurostictus: ¿Envían Diferentes Mensajes las Tasas de Cambio y la Diversidad de Tipos de Canto?
Stopover Habitat Along the Shoreline of Northern Lake Huron, Michigan: Emergent Aquatic Insects as a Food Resource for Spring Migrating Landbirds
Authors: Smith Robert J. , Moore Frank R. , May Christopher A.
Published: September 2019

Recent work in Michigan's eastern Upper Peninsula suggests that terrestrial areas bordering northern Lake Huron provide important stopover habitat for spring migrating landbirds, principally because of the presence of emergent aquatic midges (Diptera: Chironomidae). Migrants were concentrated in lakeshore habitats abundant with midges during spring migration. American Redstarts (Setophaga ruticilla) and Black-throated Green Warblers (Dendroica virens) foraged and used habitat differently, depending on their distance from the lakeshore. Here, we describe results of an integrative study in which we sampled resources, quantified American Redstart foraging behavior, and estimated mass change in American Redstarts and five other common migrant landbird species to evaluate the importance of adult midges as an early season resource for spring migrants. Resource sampling and American Redstart foraging behavior suggested that more food was available in shoreline habitats than inland during spring migration. Furthermore, migrants gained mass in shoreline habitat during stopover, which supports the argument that nearshore areas provide important stopover habitat for spring migrants. Finally, resource sampling, mass change estimates, and American Redstart foraging behavior suggested that midges and spiders (Araneae: Arachnidae) provided an important early season resource for migrating landbirds. Evidence suggests that midges were responsible for elevated spider abundance at the shoreline and that birds foraged on both midges and spiders. Midges appear to play an important role in providing high-quality stopover habitat for landbirds migrating through Michigan's eastern Upper Peninsula.

Hábitat de las Paradas Migratorias a lo Largo de la Costa Norte del Lago Huron, Michigan: Insectos Acuáticos Emergentes como Recurso Alimenticio para las Aves Terrestres Migratorias Durante la Primavera
Species Limits in Antbirds (Thamnophilidae): The Warbling Antbird (Hypocnemis Cantator) Complex
Authors: Isler Morton L. , Isler Phyllis R. , Whitney Bret M.
Published: September 2019

Six populations of Warbling Antbird (Hypocnemis cantator) currently considered subspecies are more appropriately recognized as species, given the multiplicity of vocal differences that distinguishes them. These vocal differences are as great or greater than vocal differences documented between syntopic species-pairs in the family Thamnophilidae (Isler et al. 1998). Evidence is also provided that two forms currently considered subspecies are syntopic and that two others are parapatric without apparent physical barriers. Vocally, the pair of syntopic taxa were distinguished dramatically, but solely, by common calls. The finding that common calls were as diversified as songs in this species-group suggests that calls may be as important as songs in reproductive isolation. Future field studies should therefore focus on clarifying the function of different types of thamnophilid vocalizations and elucidating their role in speciation. This is the first contribution to a multifaceted analysis of the vocalizations and genetic structure of typical antbirds (Thamnophilidae) in Amazonia. In future work, results of the vocal analysis will be compared with a parallel genetic study, after which the two analyses will be integrated to suggest a phylogeny. The present study and preliminary studies of genetic differentiation (e.g., Bates et al. 1999) make it clear that the H. cantator complex has had a long evolutionary history that produced greater species-level diversity than was recognized previously.

Límites de Especies en Thamnophilidae: El Complejo de Hypocnemis cantator
Daily Mass Changes in Landbirds During Migration Stopover on the South Shore of Lake Ontario
Authors: Bonter David N. , Donovan Therese M. , Brooks Elizabeth W.
Published: September 2019

Assigning conservation priorities to areas used by birds during migration requires information on the relative quality of areas and habitats. The rate at which migratory birds replenish energy reserves during stopover may be used as an indicator of stopover-site quality. We estimated the rate of mass gain of 34 landbird species during stopover at a near-shore terrestrial site on the south shore of Lake Ontario in New York during 12 migration seasons from 1999 to 2004. The average rate of mass gain was estimated by relating a measure of condition to time of capture (hour after sunrise) with linear regression. Data from 25,385 captures were analyzed. Significantly positive rates of mass change were detected for 20 of 30 species during spring migration and 19 of 21 species during autumn migration. No significantly negative trends were detected in either season. Daily rates of mass gain across all species averaged 9.84% of average lean body weight during spring migration and 9.77% during autumn migration. Our regression estimates were significantly greater than estimates from traditional analyses that examine mass changes in recaptured birds. Analyses of mass changes in recaptured birds revealed a mean daily change of −0.68% of average lean mass in spring and 0.13% in autumn. Because of sampling biases inherent in recapture analyses, the regression approach is likely more accurate when the assumptions of the method are met. Similar studies in various habitats, landscapes, and regions are required to prioritize conservation efforts targeting migratory stages of the annual cycle.

Cambios de Peso Diarios de Aves Terrestres durante las Paradas Migratorias en la Costa sur del Lago Ontario
Avian Visual Perspective on Plumage Coloration Confirms Rarity of Sexually Monochromatic North American Passerines
Authors: Eaton Muir D.
Published: September 2019

Male and female birds can exhibit striking differences in morphology (dimorphism), including exaggerated plumage structures, size differences, and feather color differences, yet most species are considered to have identical sexes. Classification of a species as sexually monochromatic (identical coloration between the sexes) has traditionally been based on human visual perception. Research over the past two decades has shown that birds see each other and the world differently than their human investigators; these visual differences, combined with objective color measurements, suggest that traditional assessments of plumage coloration may be questionable from an avian visual perspective (Cuthill et al. 1999). I tested the avian reality of human categorization of sexually monochromatic plumages for North American passerines. I found, on the basis of plumage-reflectance data and modeled avian color-discrimination thresholds, that 91.6% of the presumed sexually monochromatic species I sampled are sexually dichromatic to birds, which confirms the rarity of sexually monochromatic bird species. This study informs future work as to potential sources of plumage signals hidden from human observers and generates testable predictions regarding avian sex-recognition via plumage signals.

La Coloración del Plumaje desde la Perspectiva de la Visión de las Aves Confirma la Rareza del Monocromatismo Sexual en las Aves Paserinas de Norte América
Brood Sex Ratios are Related to Male Size but not to Attractiveness in Common Yellowthroats (Geothlypis Trichas)
Authors: Abroe Betsy , Garvin Julia C. , Pedersen Marc C. , Whittingham Linda A. , Dunn Peter O.
Published: September 2019

When the reproductive value of sons differs from that of daughters, selection will favor broods biased toward the sex that can provide greater fitness benefits. In species where female choice is based on male ornamentation, females mated to highly ornamented males may experience a reproductive advantage by skewing the brood sex ratio toward sons. In the Common Yellowthroat (Geothlypis trichas), males with larger black facial masks are more likely to gain a social mate and sire extrapair young and, as a result, have increased seasonal reproductive success. Females mated to larger-masked males could benefit if they produced more sons. Given that larger- masked males are preferred as extrapair sires, females may also benefit by producing more extrapair sons. We tested these hypotheses during a five-year study of Common Yellowthroats in Wisconsin. Contrary to our predictions, females did not produce more sons when mated to males with larger masks, and extrapair young were not more likely to be male. However, sons were more likely to be sired by males with longer tarsi, which suggests that females may respond to male body size rather than to male ornament size.

El Cociente de Sexos en las Nidadas Está Relacionado con el Tamaño de los Machos pero no con el Atractivo en Geothlypis trichas
Responses of Male Tropical Mockingbirds (Mimus Gilvus) to Variation in Within-Song and Between-Song Versatility
Authors: Botero Carlos A. , Vehrencamp Sandra L.
Published: September 2019

Despite their large vocal repertoires and otherwise highly versatile singing style, male mockingbirds (Mimus spp.) sometimes sing in a highly repetitive fashion. We conducted a playback experiment to determine the possible signal value of different syllable-presentation patterns during simulated male intrusions in the Tropical Mockingbird (Mimus gilvus), testing the hypothesis that more repetitive singing represents a stronger threat and generates a stronger aggressive response. Responses were measured in terms of approach and singing behavior and were analyzed using McGregor’s (1992) multivariate method. We also introduce the use of survival analysis for analyzing response variables for which subjects do not perform the behavior in question in at least one of the replicates (known as “right-censored variables” in the statistical literature). As predicted by theory, experimental subjects responded more aggressively to songs composed of a single note than to variable ones. However, versatility at the between-song level had an opposite effect: high song-switching rates generated stronger responses than low ones. Given the lack of a statistical interaction between within-song versatility and switching rate, we conclude that these two parameters may serve independent purposes and possibly transmit different information. We discuss the possibility that the signal value of variation in vocal versatility lies in the mediation of territorial conflicts, the attraction of female partners, the mediation of conflicts over access to reproductive females, or some combination of these functions.

Respuestas de Machos de Mimus gilvus a Variación en Versatilidad Vocal Dentro- y Entre-cantos
Arthropod Resource Partitioning Among Omnivorous Tanagers (Tangara SPP.) in Western Ecuador
Authors: Naoki Kazuya
Published: September 2019

The distribution and abundance of food are primary factors affecting resource-use patterns in birds. Many bird species eat several food types, which may differ in their distribution and overall abundance. I studied foraging ecology of seven sympatric species of Tangara at Mindo, Ecuador, to determine whether the patterns of resource use differed between two food types: arthropods and fruits. Interspecific differences in arthropod-foraging were manifested in the fine segregation of microhabitat preference combined with different habitat use. By contrast, interspecific differences in fruit-foraging were manifested in preferences for different plant genera, often associated with different habitats. No evidence was found for spatial partitioning of the same fruit species. Interspecific overlap in fruit-for- aging was 3× higher than that in arthropod-foraging, and species of Tangara that frequently joined the same mixed-species flocks differed largely in arthropod-foraging but overlapped greatly in fruit-foraging. The differences in patterns between arthropod and fruit-foraging may be explained by the different characteristics of arthropods and fruits as food resources. High sympatry of species of Tangara and other omnivorous tanagers, in general, appears to be maintained not because fruits are abundant, resulting in little competition for them, but because these tanagers specialize on different microhabitats for foraging arthropods.

Segregación de Artrópodos como Recurso Alimenticio de Tangaras Omnívoras (Tangara spp.) en el Oeste de Ecuador
Reassessing the Cowbird Threat
Authors: Zanette Liana , Haydon Daniel T. , Smith James N. M. , Taitt Mary J. , Clinchy Michael
Published: September 2019

The demographic significance of parasitism by Brown-headed Cowbirds (Molothrus ater; hereafter “cowbirds”) has been debated for years, because manipulative studies are few and mathematical models of cowbird-host systems have not led to tests of their predictions. We combine results from a cowbird- removal experiment (Smith et al. 2002, 2003) with a stochastic simulation model that we developed, to reassess the effect of cowbirds on the annual reproductive success (ARS) and nesting success in Song Sparrows (Melospiza melodia). Our model followed the breeding success of individual Song Sparrow nests and extrapolated to output variables including ARS, nest survival, and parasitism rates. We parameterized the model with field data from cowbird control sites (i.e., cowbirds not manipulated) and found that output variables matched those observed. We used the reduced parasitism rates observed on cowbird-removal sites, reran the model, and compared output with observed values. On removal sites, ARS was greater than predicted by the model, which indicates that the model failed to account for some biological phenomenon that occurred when cowbirds were in the system. To assess what this phenomenon might be, we conducted further analyses that indicated that cowbirds may facilitate nest predation by “conventional” predators. Using elasticity analyses, we show that cowbirds have their largest effect on ARS through egg removal and that conventional predators are more important than cowbirds in directly affecting nest survival rates. We report that to assess the effect of cowbirds on nest survival, researchers must avoid using the common technique of comparing survival rates of parasitized and unparasitized nests within populations.

Réévaluation de la Menace du Vacher
Vigilance Behavior in the Harlequin Duck (Histrionicus Histrionicus) During the Preincubation Period in Labrador: Are Males Vigilant for Self or Social Partner?
Authors: Squires Kelly A. , Martin Kathy , Goudie R. Ian
Published: September 2019

Males of several avian species are more vigilant than their female partners, particularly during the preincubation period. Male vigilance may function as a deterrent of extrapair copulation attempts (EPCs) or to ensure male survival, because males of sexually dimorphic species may be more conspicuous to predators than females. However, vigilant males may act as antipredator sentinels to enhance female survivorship, which may also allow females to feed and rest more efficiently, thereby enhancing their ability to form clutches. We attempted to distinguish between the “male benefits” and “female benefits” hypotheses by studying the behavior of unpaired males and paired Harlequin Ducks (Histrionicus histrionicus) during the preincubation period. Paired males were, on average, four times more vigilant than unpaired males and their mates, which suggests that elevated levels of vigilance by paired males does not function primarily for self-protection against predators. Males were not more vigilant during the female’s fertile period, contrary to the “paternity assurance” hypothesis. Male vigilance during feeding bouts was highest when pairs fed alone near shore—a condition in which feeding was likely more “risky.” Male vigilance was positively correlated with female feeding when females fed near shore, but not at other times. During resting bouts, males were vigilant 14 ± 0.01% of the time in all conditions. We suggest that male vigilance may be important to enhance female survival, especially when females feed under risky conditions.

Comportement de Vigilance chez Histrionicus histrionicus durant la Période de Pré- incubation au Labrador: Les Mâles Sont-ils Vigilants pour Eux-mêmes ou pour leur Partenaire Social?
Return Rate, Fidelity, and Dispersal in a Breeding Population of Flammulated Owls (Otus Flammeolus)
Authors: Linkhart Brian D. , Reynolds Richard T.
Published: September 2019

We estimated annual return rate, fidelity, and breeding dispersal in a migratory population of Flammulated Owls (Otus flammeolus) in central Colorado. Return rates, based on capture-recapture histories of 39 males and 52 females from 1981 to 2003, were higher for males (84%) than for females (45%). Annual recapture probability was higher for females, because breeders are easier to capture than nonbreeders and females always attempted to nest, whereas some males were unpaired (did not nest) for up to four years. Territory fidelity was male biased (92%, vs. 56% for females, adjusted for undetected emigration), and mean tenure on territories was more than twice as long for males as for females. Females, but not males, had lower return rates to territories in the year following nesting failure compared with females whose nests were successful. Most males appeared to occupy one territory their entire reproductive lives, countering predictions of habitat-selection models that individuals should move to higher-quality habitats when they become available. We estimated that 74% of pairs retained the same mate in consecutive nesting attempts, but mates that bred together for multiple years had no reproductive advantages over mates that bred together for the first time. In most cases, females dispersed from territories if their mates did not return. When females dispersed, they went to territories where total productivity over the study and lifetime reproductive success of new mates were higher than on original territories, which supports the hypothesis that dispersal by females increases individual fitness.

Tasa de Retorno, Fidelidad y Dispersión en una Población Reproductiva de Otus flammeolus
Annual Variation in the Benefits of a Nesting Association Between Red Phalaropes (Phalaropus Fulicarius) and Sabine's Gulls (Xema Sabini)
Authors: Smith Paul A. , Gilchrist H. Grant , Smith James N. M. , Nol Erica
Published: September 2019

By nesting near aggressive birds, timid species can reap the benefits of aggressive nest defense while avoiding the costs. Red Phalaropes (Phalaropus fulicarius; hereafter “phalaropes”) typically nest in grass-sedge marshes, but nests have also been noted in rocky coastal habitats. We studied the reproductive ecology of phalaropes at East Bay, Southampton Island, Nunavut, to determine whether their use of coastal nest areas reflected a protective nesting association with an aggressive larid, the Sabine's Gull (Xema sabini; hereafter “gull”). From 2000 to 2002, we found and monitored 29 phalarope nests with gull nests nearby (≤150 m away) and 26 without gulls nearby. Coastal phalarope nests were nearer to gull nests than expected by chance. No habitat differences were detected between coastal areas with and without gull nests, but only three phalarope nests were found in coastal areas without gull nests. Thermistor probes inserted in phalarope nests revealed that incubators with gulls nearby behaved less cryptically, taking more frequent and longer incubation recesses. In human-approach experiments, phalaropes with gulls nearby flushed earlier than those without gulls. In 2000 and 2001, hatch success was 17–20% higher for phalaropes with gulls nearby, but these nests had lower success rates than those without nearby gulls in 2002. These gulls are able to defend their nests from avian predators only; in 2002, arctic foxes (Alopex lagopus) were abundant, and their primary prey, collared lemmings (Dicrostonyx torquatus), were scarce. We suggest that phalaropes select coastal areas near gulls, but that this association is beneficial to phalaropes only in years when egg predation by arctic foxes is low.

Variation Annuelle des Bénéfices d'une Association pour Nicher entre Phalaropus fulicarius et Xema sabini
Plumage Development and Molt in Long-Tailed Manakins (Chiroxiphia Linearis): Variation According to Sex and Age
Authors: Doucet Stéphanie M. , McDonald David B. , Foster Mercedes S. , Clay Rob P.
Published: September 2019

Lek-mating Long-tailed Manakins (Chiroxiphia linearis) exhibit an unusual pattern of delayed plumage maturation. Each year, males progress through a series of predefinitive plumages before attaining definitive plumage in their fifth calendar year. Females also exhibit variation in plumage coloration, with some females displaying male-like plumage characteristics. Using data from mist-net captures in northwest Costa Rica (n = 1,315) and museum specimens from throughout the range of Long-tailed Manakins (n = 585), we documented the plumage sequence progression of males, explored variation in female plumage, and described the timing of molt in this species. Males progressed through a series of age-specific predefinitive plumages, which enabled the accurate aging of predefinitive-plumaged males in the field; this predefinitive plumage sequence is the basis for age-related status-signaling in these males. Females tended to acquire red coloration in the crown as they aged. However, colorful plumage in females may be a byproduct of selection on bright male plumage. Females exhibited an early peak of molt activity from February to April, little molt from May through July, and a second, more pronounced peak of molt activity in October. By contrast, males in older predefinitive-plumage stages and males in definitive plumage exhibited comparable unimodal distributions in molt activity beginning in June and peaking between July and October. Our data are consistent with selective pressure to avoid the costs of molt-breeding overlap in females and older males. Our findings have important implications for social organization and signaling in Long- tailed Manakins, and for the evolution of delayed plumage maturation in birds.

Desarrollo del Plumaje y Muda en Chiroxiphia linearis: Variación de Acuerdo al Sexo y la Edad
Density, Territory Size, and Long-Term Spatial Dynamics of a Guild of Terrestrial Insectivorous Birds Near Manaus, Brazil
Authors: Stouffer Philip C.
Published: September 2019

From 1994 to 2003, I annually surveyed terrestrial insectivorous birds in a 100-ha plot within continuous rainforest near Manaus, Brazil. I used spot-map registrations and radiotagged birds to estimate territory size and density on the plot for 13 species. As in the few previous studies of Amazonian birds, territory sizes were large (mean = 13.0 ha) and densities were low (mean = 3.4 pairs per 100 ha). The most common species, Formicarius colma, was the only species with >10 pairs per 100 ha, and one of four species (with Myrmeciza ferruginea, Conopophaga aurita, and Corythopis torquatus) to have territories of <7.0 ha. On average, each species occupied 34% of the plot, with only four species (F. colma, Grallaria varia, F. analis, and M. ferruginea) ever occupying >50% in any year. Territories appeared and disappeared between surveys; ∼71% of territories detected in a given survey were present in the next survey. The two rarest species, Myrmothera campanisona and Hylopezus macularius, were absent from the plot in some years. Across species, territory stability was positively correlated with abundance; more common species had more stable density among years than rare species. Although past research has shown territory stability for the most common species of Neotropical rainforest birds, my results suggest that rarer species, which constitute the bulk of the avifauna, may show greater fluctuation in abundance.

I compared my results to similar data from lowland rainforests in Panama, French Guiana, Ecuador, and Peru. Species richness was lowest in Panama, but comparable among the Amazonian sites. Panama also had the highest biomass and smallest territory sizes. Interestingly, relative abundances of species shared among sites were not necessarily similar. With the exception of Conopophaga spp., all species or replacement species shared among sites were at least twice as abundant at one site as at another. Relative abundance within genera also differed among sites for Sclerurus and Formicarius. The sparse data available so far suggest that individual species show considerable spatial variation in abundance across Amazonia, though the mechanisms and the texture of the patterns remain unknown.

Densidade, Tamanho do Território, e Dinamismo Espacial ao Longo Prazo das Aves Insetívoras Terrestres perto de Manaus, Brasil
Egg Size, Eggshell Porosity, and Incubation Period in the Marine Bird Family Alcidae
Authors: Zimmermann Karen , Hipfner J. Mark
Published: September 2019

Although the ultimate factors that influence the duration of avian incubation periods are well known, we know much less about the proximate mechanisms by which birds adjust incubation period in response to selection. We tested the hypothesis that an adjustment in eggshell porosity is one such proximate mechanism (i.e., that avian species with higher ratios of incubation period to egg size lay eggs with less porous shells). Eggshell porosity affects the rate of gaseous exchange between the developing embryo and the external environment; thus, to the extent that embryonic metabolism is diffusion-limited, eggshell porosity could directly determine incubation period. To test that hypothesis, we collected eggs from seven species of Alcidae, a family of marine birds that exhibits an unusual degree of interspecific variation in incubation period, and measured egg mass and eggshell porosity (determined by the number and size of pores and the thickness of the shell). Incubation periods were obtained from the literature. Egg mass and eggshell porosity combined explained 87% of the variation in incubation period among the seven species, which included at least one member of each of the six main alcid lineages. As predicted, eggshell porosity and incubation period were negatively related, after controlling for egg mass. Our results are consistent with the hypothesis that evolutionary changes in avian incubation period may be attributed, at least in part, to adjustments in eggshell porosity.

Taille de l’Œuf, Porosité de la Coquille et Période d’Incubation chez les Oiseaux Marins de la Famille des Alcidés