Showing papers in "The Auk in 2003"
TL;DR: To minimize device effects, it is suggested that transmitter loads be reduced to a minimum, use of harnesses be avoided, and careful attention be given to limiting handling times during incubation when some species are particularly sensitive to disturbance.
Abstract: Effects of deployment of miniaturized transmitters and loggers have been well studied in penguins, but much less so in flying seabirds. We examined the effects of satellite tag (platform terminal transmitter, PTT) deployment in Black-browed (Thalassarche melanophris) and Gray-headed (T. chrysostoma) albatrosses at South Georgia and reviewed the recent literature for other albatrosses and petrels. In our study, although a few individuals may have slightly extended their foraging trips, overall there was no significant difference in trip duration, meal mass, breeding success, or rate of return in the next season between birds with PTTs and controls. By comparison, most other studies of albatrosses and petrels recorded extended trip durations and, in some cases, high rates of nest desertion following PTT attachment. That occurred particularly where transmitter loads exceeded 3% of adult mass. Extended trip durations may result from reduced flight efficiency, as well as the effect of capture and temp...
522 citations
TL;DR: In this article, the authors 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 opinion of the editors or any official policy of the American Ornithologists' Union.
Abstract: Abstract 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.
481 citations
TL;DR: It is demonstrated that the color diversity of melanin ornaments is quite broad, including red, orange, yellow, and green, in addition to black and brown, and it is perhaps incorrectly assumed that melaninOrnaments are typically black or blackish-brown and thus show both less variation within species and less diversity across species than do carotenoids.
Abstract: MANY STUDIES OF sexual selection have focused on the role of ornaments in mate choice (see Andersson 1994, Espmark et al. 2000). Birds have been a favorite taxon for those studies because of the prevalence of conspicuous ornaments, including brightly colored feathers, skin, and bills, and dramatically elongated feathers or feathers of elaborate structure. The colors of avian ornaments are the result of carotenoids, melanins, tissue structure, or some combination thereof. Carotenoid ornaments (e.g. bright reds, oranges, and yellows) have generated much interest. Those pigments can not be synthesized de novo by animals, but rather must be included in the diet (Brush 1990). That allows for the possibility that they are limited in nature or diffi cult to obtain (Hill 1994, 1996; Hudon 1994; Linville and Breitwisch 1997). Additionally, carotenoids have been implicated in a variety of critical physiological functions in animals. That recognition has stimulated much recent research on mate choice of carotenoid advertisement and the indicator value of carotenoid ornaments for several important aspects of individual condition. Avian melanin ornaments have also received considerable research attention. In contrast to studies of carotenoid ornaments, however, the primary focus of studies of melanin ornaments has been on the advertisement of melanin “badges” in intrasexual competition. Thus, the associations among expressions of melanin ornaments, mate choice, and individual condition have not been made to the same degree as for carotenoids. There are several possible reasons for that. First, melanins not only color ornaments but are also the basis of most inconspicuous appearances (i.e. camoufl age), in contrast to the highly conspicuous carotenoids. Second, melanins are synthesized by animals and thus do not need to be included in the diet. Finally, it is perhaps incorrectly assumed that melanin ornaments are typically black or blackish-brown and thus show both less variation within species and less diversity across species than do carotenoid ornaments. Here, we review a variety of aspects of the biology of avian melanin ornaments. We demonstrate that the color diversity of melanin ornaments is quite broad, including red (e.g. Red Junglefowl and Barn Swallow [Hirundo rustica]), orange (e.g. Red Junglefowl), yellow (e.g. Western Tanager [Piranga ludoviciana]), and green (e.g. Mallard), in addition to black and brown. Color differences in all melanin ornaments are, in part, a function of the ratio of the two types of melanins contained, and we outline the intriguingly different metabolic pathways to the formation of the two different categories of melanins. There are likely to be both signifi cant physiological benefi ts and costs to melanin production, and those may well differ for the two types of melanins. Finally, we Department of Biology, University of Dayton, Dayton, Ohio 45469-2320, USA JODIE M. JAWOR1 AND RANDALL BREITWISCH MELANIN ORNAMENTS, HONESTY, AND SEXUAL SELECTION The Auk 120(2):249–265, 2003
291 citations
TL;DR: This paper used distance sampling with line transects to investigate differences in detection probabilities among observers and among three species of grassland songbirds: Henslow's Sparrow, Grasshopper Sparrow (A. savannarum), and Savannah Sparrow (Passerculus sandwichensis).
Abstract: Differences among observers in ability to detect and identify birds has been long recognized as a potential source of error when surveying terrestrial birds. However, few published studies address that issue in their methods or study design. We used distance sampling with line transects to investigate differences in detection probabilities among observers and among three species of grassland songbirds: Henslow's Sparrow (Ammodramus henslowii), Grasshopper Sparrow (A. savannarum), and Savannah Sparrow (Passerculus sandwichensis). Our review of 75 papers published in 1985–2001 found that the most commonly used methods were fixed-width transects (31%, 23 papers) and fixed-radius point counts (20%, 15 papers). The median half-width of fixed-width strip transects used by researchers was 50 m, but our results indicated detection probabilities were 25 m for most observers and species. Beyond 50 m from the transect line, we found that as many as 60% of birds were missed by observers an...
235 citations
TL;DR: For example, this paper found that changes in agricultural land use within the eastern and central U.S. have driven population trends of grassland and shrub habitat birds over the past two decades.
Abstract: State-level Breeding Bird Survey (1980–1998) and U.S. Department of Agriculture statistics were used to test the hypothesis that changes in agricultural land use within the eastern and central U.S. have driven population trends of grassland and shrub habitat birds over the past two decades. The degree to which population trends differed between grassland and shrub habitats was evaluated with respect to migratory and nesting behavior. Grassland birds declined significantly between 1980 and 1999, but, on average, shrub habitat species did not. Grassland-breeding, long-distance migrants exhibited the strongest negative trends. Most species (78%; n = 63) exhibited at least one significant association between population trends and changes in agricultural land use, and in most, land use “explained” 25–30% of the variation in population trends among states. Changes in the farmland landscape accounted for more of the interstate variability of population trends of short-distance migrants than of both long...
233 citations
TL;DR: Within the last two decades, radar ornithology has played an increasingly important role in conservation of species that are migratory, endangered, threatened, or of special concern.
Abstract: IN THE APPROXIMATELY 60 years since the discovery that birds were responsible for some of the puzzling radar echoes dubbed “angels” by the British (Lack and Varley 1945, Buss 1946), radar has proven to be a useful tool for the detection, monitoring, and quantifi cation of bird movements in the atmosphere (Eastwood 1967; Richardson 1979; Vaughn 1985; Bruderer 1997a, b). Radar has been a particularly valuable tool for descriptive studies of daily and seasonal patterns of bird migration, but the technique has also been used to answer important questions about how birds orient during migration and the role of atmospheric structure in shaping fl ight strategies of birds. Within the last two decades, radar ornithology has played an increasingly important role in conservation of species that are migratory, endangered, threatened, or of special concern. TYPES OF RADAR
182 citations
174 citations
TL;DR: Evaluated the effects of using miniature video camera systems to document predation events, identify grassland passerine nest predators in grazed pastures, and determine whether predation patterns of nest predators known to prefer wooded edges differed from those of other nest predators.
Abstract: Fragmentation of grassland habitat may increase predation rates on grassland passerine nests and contribute to population decline of several species. Studies that simultaneously document the nest predator community and associate predator species with edges created by fragmentation have not been conducted for grassland habitats. The purpose of our study was to evaluate the effects of using miniature video camera systems to document predation events, identify grassland passerine nest predators in grazed pastures, and determine whether predation patterns of nest predators known to prefer wooded edges differed from those of other nest predators. In 1998–2000, we deployed cameras at 89 nests of Savannah Sparrows (Passerculus sandwichensis), Grasshopper Sparrows (Ammodramus savannarum), Song Sparrows (Melospiza melodia), meadowlarks (Sturnellaspp.), and Bobolinks (Dolichonyx oryzivorus) in southwestern Wisconsin pastures 16–169 ha in size. Abandonment rates were higher for nests with cameras than for n...
168 citations
TL;DR: This article used data from statewide surveys of riparian birds in Utah, 1992-1998, to compare relative abundance and distance-sampling methods, finding that point-count methods failed to reasonably meet the fundamental assumption of constant proportionality, with estimated detectability varying 3- to 5-fold despite the use of widely accepted and well-standardized methods.
Abstract: We used data from statewide surveys of riparian birds in Utah, 1992–1998, to compare relative-abundance and distance-sampling methods. By generating relative-abundance indices with point-count methods and density with point-transect sampling methods, we examined whether the assumptions underlying each method were met during field surveys for four bird species (Brown-headed Cowbird [Molothrus ater], Bullock's Oriole [Icterus bullockii], Warbling Vireo [Vireo gilvus], and Yellow Warbler [Dendroica petechia]). Point-count methods failed to reasonably meet the fundamental assumption of constant proportionality, with estimated detectability varying 3- to 5-fold despite the use of widely accepted and well-standardized methods. Population trends based on relative abundance were subsequently unstable, often varying in both magnitude and direction with the survey plot radius used (25 m, 50 m, or unlimited distance). Distance-sampling methods appeared to meet critical assumptions, were robust to assumption...
158 citations
TL;DR: In this article, the authors explored large-scale migratory responses of land birds encountering the Great Lakes as revealed by weather surveillance radars (WSR-88D) and two smaller specialized radars.
Abstract: The Great Lakes and nearby agricultural midwestern United States together represent a geographical challenge to migratory land birds during flight and stopover. We explored large-scale migratory responses of land birds encountering the Great Lakes as revealed by weather surveillance radars (WSR-88D) and two smaller specialized radars. Those responses reveal comprehensive landscape- or regional-scale migratory patterns that would otherwise have been difficult to infer. Analysis of radar echoes showed birds crossed the Great Lakes in large numbers, although we also found evidence of birds avoiding lake crossing in some locations. Around dawn, birds over water in numerous locations frequently exhibited an increase in migratory height (dawn ascent) and often an accompanying reorientation toward nearest land if they were within ∼28 km of shore. Those behavioral responses to the Great Lakes influence the resulting distribution of birds stopping over in the intervening terrestrial landscapes.
155 citations
TL;DR: In this article, the authors present a survey of the major museums in the United States, including the National Museum of Natural History (NMNH), Bell Museum, Museum of Vertebrate Zoology (MVZ), Museum of Biology, Cornell Laboratory of Ornithology, 159 Sapsucker Woods Road, Ithaca, New York 14850, USA; and Michigan State University Museum and Department of Zoology, West Circle Drive, East Lansing, Michigan 48824, USA.
Abstract: 1U.S. Geological Survey, Patuxent Wildlife Research Center, National Museum of Natural History, MRC-111, P.O. Box 37012, Washington, D.C. 20013, USA; 23201 Circle Hill Road, Alexandria, Virginia 22305, USA; 3Bell Museum of Natural History, 10 Church Street, University of Minnesota, Minneapolis, Minnesota 55455, USA; 4Museum of Vertebrate Zoology, 3101 Valley Life Sciences Building, University of California, Berkeley, California 94720, USA; 524 Idaho Street, Bishop, California 93514, USA; 6Florida Museum of Natural History, P.O. Box 117800, University of Florida, Gainesville, Florida 32611, USA; 7Cornell Laboratory of Ornithology, 159 Sapsucker Woods Road, Ithaca, New York 14850, USA; 8Michigan State University Museum and Department of Zoology, West Circle Drive, East Lansing, Michigan 48824, USA; 9Museum of Natural Science, Louisiana State University, Foster Hall 119, Baton Rouge, Louisiana 70803, USA; 10Department of Ecology and Evolutionary Biology, Ramsay Wright Labs, University of Toronto, Toronto, Ontario M5S 3G5, Canada; 11Environment, Culture and Conservation, Field Museum of Natural History, 1400 S. Lake Shore Drive, Chicago, Illinois 60605, USA; and 12University of Alaska Museum, 907 Yukon Drive, Fairbanks, Alaska 99775, USA
TL;DR: The results are the first rigorous demonstration that preen oil is important for plumage condition in nonwaterfowl and that it has insecticidal properties and that reduction in plumages condition on birds without glands is due to an increase in ectoparasites.
Abstract: Most species of birds have a uropygial gland, also known as a preen gland, which produces oil that birds spread through their plumage when preening. The plumage of waterfowl deprived of uropygial oil becomes brittle and is subject to breakage. For other groups of birds, however, the importance of preen oil remains unclear. Previous workers have argued that preen oil may serve little or no function in Columbiforms (pigeons and doves). We tested that assertion by removing uropygial glands from Rock Doves (Columba livia) and assessing their plumage condition after several months. The results of that experiment showed significant degradation of plumage in the absence of oil. Our results are the first rigorous demonstration that preen oil is important for plumage condition in nonwaterfowl. We tested one possible function of preen oil—that it has insecticidal properties and that reduction in plumage condition on birds without glands is due to an increase in ectoparasites. We tested that hypothesis for ...
TL;DR: A novel phylogenetic marker, a region of the nuclear gene ornithine decarboxylase (ODC) spanning from exon 6 to exon 8, was sequenced in 10 oriole species, supporting the conclusion that plumage evolution in the New World orioles has been highly homoplastic.
Abstract: A recent study of New World orioles (Icterus spp.), which traced a large number of plumage characters onto a mitochondrial DNA phylogeny, reported high frequencies of evolutionary convergence and reversal of plumage characters (Omland and Lanyon 2000). Although those results are consistent with other smaller scale studies that have documented plumage homoplasy, the mitochondrial genome is inherited as a single linkage group, so mitochondrial data represent only one gene tree. The mitochondrial (mt) DNA tree may not reflect the true evolutionary history of a lineage; therefore, it remains possible that the plumage characters could reflect the true species phylogeny. Other rapidly evolving regions of DNA can provide independent phylogenetic hypotheses useful for evaluating mitochondrial gene trees. A novel phylogenetic marker, a region of the nuclear gene ornithine decarboxylase (ODC) spanning from exon 6 to exon 8, was sequenced in 10 oriole species. The resultant nuclear gene tree reconstructs th...
TL;DR: Results suggest that physiological factors such as pigment transport may play a more important role in shaping variability in carotenoid-based bill coloration in this species than does diet.
Abstract: Carotenoid-based colors serve important sexual-signaling functions in many animals, but the proximate factor(s) underlying their expression has sparked controversy. In particular, the relative contributions of dietary and physiological mechanisms have been questioned of late. However, no studies have concurrently quantified levels of food intake or pigment processing in any species to examine the comparative effects of pigment acquisition and use on integumetary coloration. Here, we studied within- and between-sex patterns of food intake and plasma pigment circulation in the Zebra Finch (Taeniopygia guttata) to assess how sexually dichromatic, carotenoid-based bill pigmentation serves as an indicator of pigment access in the diet and carotenoid transport through the bloodstream. First, in a food-choice study, we found that males and females did not consume different types or amounts of food, despite dramatic sex differences in bill coloration. Similarly, variability in carotenoid-based bill pigme...
TL;DR: The evolution of long-distance migration in and the historical biogeography of Catharus thrushes is addressed and uncertainty in ancestral character states presents an interesting scenario including potential drop-offs of resident species from migratory ancestors.
Abstract: We addressed the evolution of long-distance migration in and the historical biogeography of Catharus thrushes within a phylogenetic framework. Catharus thrushes are a Nearctic–Neotropical genus consisting of five migrant and seven resident species. We reconstructed a molecular phylogeny using a combined analysis of cytochrome-b and ND2 genes. Phylogenetic reconstructions indicate the nonmonophyly of migratory Catharus species. The Neotropics are the most likely ancestral geographic area for the entire lineage, and migratory species are sister to resident taxa whose ranges are restricted to Central America, Mexico, or both. Resident behavior may be ancestral within the lineage, with migratory behavior evolving three times, although confidence in those reconstructions is equivocal in many cases. However, uncertainty in ancestral character states presents an interesting scenario including potential drop-offs of resident species from migratory ancestors.
TL;DR: In this paper, a logistic regression model was developed based on the presence or absence of foraging signs in an eastern black spruce (Picea mariana) boreal forest in Quebec, Canada.
Abstract: We studied snag use for foraging by Black-backed Woodpeckers (Picoides arcticus) one year after a fire in an eastern black spruce (Picea mariana) boreal forest in Quebec, Canada. We searched for signs of foraging (bark flaking and excavation holes) by Black-backed Woodpeckers on 6,536 snags sampled in 56 plots located in portions of the burned forest that had not been salvage logged. A logistic regression model was developed based on the presence or absence of foraging signs. Results showed that Black-backed Woodpeckers used larger snags that were less deteriorated by fire (qualified as high-quality snags). Direct field observations of individuals foraging on 119 snags also indicated that used snags corresponded to those of high predicted quality. Finally, we assessed the relationship between food availability and snag characteristics by measuring the density of wood-boring beetle larvae holes on 30 snags of different size and deterioration classes. High-quality snags contained higher prey densit...
TL;DR: A model based on locomotion and life history that integrates nesting biology, fl ight capacity, body mass, morphological modularity, and stage at hatching among extant avian clades is offered.
Abstract: AVIAN NESTING STRATEGIES, flight style, hatchling and adult body size, developmental precocial–altricial trajectories, and the origin of fl ight are frequently studied as separate topics rather than addressed as integrated and mutually dependent phenomena. Consider the following questions: What is the evolutionary basis of the precocial-to-altricial developmental spectrum observed among birds? Does fl ight profi ciency correlate with aspects of nesting biology among extant avian species? Are there reasonable alternative hypotheses to the popular arboreal–cursorial dichotomy regarding the origin of avian fl ight? In an attempt to address the above questions, I offer a model based on locomotion and life history that integrates nesting biology, fl ight capacity, body mass, morphological modularity, and stage at hatching among extant avian clades. Acknowledging that those variables are neither independent nor mutually exclusive, I suggest that the range and tendency for each factor be compared simultaneously and within an integrated matrix. Using a broad-brush approach, I provide a fi rst approximation of a synthetic viewpoint for evaluating locomotor and life-history features of birds. In addition, phylogenetic correlates are discussed in hope of stimulating future studies that test that thesis among living and extinct clades. I begin with a brief review of each of the fi ve criteria embedded in the model.
TL;DR: Although higher DNA concentration improved success, PCR fragment size had a much stronger influence on the success and repeatability of microsatellite amplification, which suggests that the accuracy and efficiency of genotyping can be improved most easily by designing primers that amplify smaller DNA fragments.
Abstract: We address the problem of microsatellite genotyping errors associated with polymerase chain reaction (PCR) amplification from degraded and dilute template DNA and provide suggestions for improving the accuracy of genotype data in studies using older museum specimens as a source of DNA. In the course of a population genetics study of African indigobirds (Vidua spp.), we used replicate PCR to evaluate genotyping reliability for nine microsatellite loci in relation to PCR fragment length and DNA template concentration (DNA extracted from the calamus of one vs. two wing feathers). Complete amplification failure and the dropout of one allele from heterozygous genotypes were the predominant problems encountered. For samples with heterozygous genotypes, allele dropout occurred in 19.2 and 12.1% of PCR using extracts derived from one and two feathers, respectively. The amplification of artifact bands was less frequent (affecting 4.9 and 1% of positive PCR reactions with one- and two-feather extracts, res...
TL;DR: The hypothesis that individuals with limited opportunities to breed can modulate the adrenocortical stress response when reproductive effort or investment is greatest as a way to maximize breeding success is supported.
Abstract: Modulation of the adrenocortical stress response with respect to the degree of parental activity was investigated in three Arctic-breeding species of songbirds faced with limited opportunities to breed. The hypothesis that the strength of the response can be lowered when reproductive effort or investment is greatest was tested by measuring the adrenocortical response to handling stress during two breeding stages that represented different levels of reproductive effort (i.e. before young were present [preparental] and while feeding nestlings [parental]). Comparisons of the corticosterone stress response (baseline at capture and subsequent samples 5, 10, 30, and 60 min after capture) were made within and between both sexes of American Tree Sparrows (Spizella arborea), White-crowned Sparrows (Zonotrichia leucophrys gambelii), and Savannah Sparrows (Passerculus sandwichensis) breeding above the Arctic Circle at Toolik Lake, Alaska. In general, body mass and baseline corticosterone did not differ betw...
TL;DR: In this paper, the authors identify specifi c factors inflencing small populations, but the applicability of those results across broad geographic areas is often uncertain, but correlations between broad patterns of changes in bird populations and land-use characteristics provide a basis for directing future studies conducted at smaller geographic scales.
Abstract: AT THE BEGINNING of the twentieth century, prospects for bird populations occupying farmlands were promising. Agricultural expansion and the resulting deforestation produced wholesale changes to the landscape of eastern North America (Trautman 1977, Zeranski and Baptist 1990, Nicholson 1997). Regional avifaunas were transformed as Horned Larks (Eremophila alpestris), Dickcissels (Spiza americana), and other farmland birds undertook range expansions (Hurley and Franks 1976, Askins 1999). Those farmland birds became conspicuous, frequently in numbers that are hard to imagine today (Trautman 1940). One hundred years later, many of those once plentiful species experienced dramatic population declines (Askins 1993, Peterjohn and Sauer 1999). Those trends were evident for many decades, although pre-1965 trends were largely based on anecdotal accounts and were frequently attributed to changing regional landscapes due to urban expansion, farm abandonment resulting in increased forest cover, and the more intensive use of remaining agricultural fi elds (Trautman 1940, Herkert 1991, Askins 2000). However, numerous specifi c factors were implicated in local declines of individual species (Kantrud 1981, Bollinger et al. 1990, Lymn and Temple 1991, Bowen and Kruse 1993, Herkert 1994, Houston and Schmutz 1999, Blackwell and Dolbeer 2001). Understanding factors responsible for population changes can be approached at various geographic scales. Local studies identify specifi c factors infl uencing small populations, but the applicability of those results across broad geographic areas is often uncertain. Studies conducted at large geographic scales identify broad patterns of change, but those patterns frequently involve interrelated factors that may be only loosely related to the actual causes of population change. However, correlations between broad patterns of changes in bird populations and land-use characteristics provide a basis for directing future studies conducted at smaller geographic scales.
TL;DR: The data suggest that suburban scrub-jays with access to predictable sources of high-quality human-provided foods accumulate endogenous protein that can be used to breed earlier than jays in wildland habitats.
Abstract: Timing of breeding in Florida Scrub-Jays (Aphelocoma coerulescens) varies both within and between years. Social status and breeding experience may explain much of the within-year variation, but the availability of certain foods may partially explain between-year patterns. Scrub-jays in suburban habitats with access to unlimited human-provided foods breed earlier and with less between-year variation in timing of breeding than jays in wildland habitats. We hypothesized that those differences in timing of breeding result from access to human-provided foods in the suburban site. Human-provided food may influence timing of breeding by improving the overall body condition of females, or it may influence breeding by providing nutrients essential for breeding. If condition mediated, breeding females in the two habitats should differ in certain physiological parameters relative to time before egg laying and calendar date. If the effect is not related to body condition, we expect differences in prebreeding...
TL;DR: The molecular phylogeny challenges the traditional classification of the Timaliidae and suggests that the babblers assemblage includes two other oscine taxa traditionally considered to be distantly related, Sylvia (Sylviidae) and Zosterops (Zosteropidae).
Abstract: The systematics of the babblers (Timaliidae) and related members of the Old World insectivorous passerines have been particularly difficult. To clarify our understanding of this group, phylogenetic relationships were constructed using sequences of three mitochondrial genes (cytochrome b, rRNA 12S and 16S). The results indicated that several species traditionally placed among babblers, the shrike babblers (Pteruthius) and the Gray-chested Thrush Babbler (Kakamega poliothorax), are not related to the Timaliidae, but belong to other passerine groups. Furthermore, the phylogenetic hypotheses inferred from molecular data suggest that the babblers assemblage includes two other oscine taxa traditionally considered to be distantly related, Sylvia (Sylviidae) and Zosterops (Zosteropidae). The polyphyly of several babbler genera is discussed, with particular attention to the laughingthrushes (genera Garrulax and Babax) for which the phylogeny is compared to previous hypotheses of relationships. Results fro...
TL;DR: In this article, the authors report how different types of edges surrounding patches may affect spatial distributions of Bobolink (Dolichonyx oryzivorus), a declining, area-sensitive songbird that breeds in grasslands.
Abstract: Habitat edges are well-studied components of fragmented landscapes, yet factors mediating edge effects remain unclear. We report how different types of edges surrounding patches may affect spatial distributions of Bobolink (Dolichonyx oryzivorus), a declining, area-sensitive songbird that breeds in grasslands. We expected Bobolinks to be less abundant near edges, and we investigated a set of alternative hypotheses for explaining that spatial pattern: (1) passive displacement, in which individuals do not avoid edges but use edges as boundaries for territories; (2) habitat gradients, in which individuals respond to habitat structure gradients near edges; (3) territory size, in which size of territories increases near edges; and (4) active avoidance, in which individuals actively avoid edges by positioning territory boundaries away from edges. To examine those hypotheses, we surveyed Bobolinks in grassland habitats near 34 edges of three different edge types (agriculture, road, and woodland) in nort...
TL;DR: In this paper, the authors studied 237 breeding attempts of Spanish Imperial Eagles (Aquila adalberti) in Donana National Park (southwestern Spain), including 29 pairs with at least one immature member, to investigate age-related effects on population fertility.
Abstract: Over a period of 19 years, we studied 237 breeding attempts of Spanish Imperial Eagles (Aquila adalberti) in Donana National Park (southwestern Spain), including 29 pairs with at least one immature member, to investigate age-related effects on population fecundity. Without considering effect of territory quality, adult pairs were signifi cantly more productive than immature pairs. Highly signifi cant differences in breeding performance among territories were independent of age-classes of birds occupying them. Low-quality territories were more frequently occupied by immature pairs, whereas high-quality territories were occupied mostly or exclusively by adult birds. Therefore, age and territory quality appear to be interrelated. We found no effect on average population fecundity due to breeding by immature pairs. Received 13 November 2001, accepted 26 October 2002. RESUMEN.—Para estudiar los efectos relacionados con la edad sobre la fecundidad de la poblacion de Aguilas Imperiales Ibericas (Aquila adalberti) en el Parque Naconal de Donana (SO Espana), analizamos 237 intentos de nidifi cacion, incluyendo 29 de parejas con al menos un miembro inmaduro, a lo largo de un periodo de 19 anos. Sin considerar el efecto de la calidad de territorio, las parejas de adultos fueron signifi cativamente mas productivas que las parejas con inmaduros. Las diferencias altamente signifi cativas en los resultados reproductivos entre territorios fueron independientes de la clase de edad de los individuos que los ocupaban. Los territorios de baja calidad eran mas frecuentemente ocupados por parejas con inmaduros, mientras que los territorios de alta calidad fueron ocupados mayoritaria o exclusivamente por aves adultas. Por tanto, la edad y la calidad del territorio estan interrelacionadas. No encontramos ningun efecto de la nidifi cacion de inmaduros sobre la fecundidad media de la poblacion.
TL;DR: In this paper, the authors extend the capturemark-recapture approach by supplementing known residents with those previously unmarked birds captured twice or more, at least d days apart, within a season.
Abstract: Capture-mark-recapture studies provide a useful mechanism for estimating the components of the population dynamics of birds, especially survival. In such studies, it is important that the population being captured matches the population of interest. In many studies, transients are captured along with the population of interest (e.g. resident breeders). Ignoring that phenomenon produces negatively biased survival estimates, because transients do not return. Although transients cannot be distinguished from residents in the hand, previous methods have adjusted for transience by relying on those captured in more than one year to provide direct estimates of survival rate for residents. Here, we extend that approach by supplementing that cohort of known residents with those previously unmarked birds captured twice or more, at least d days apart, within a season. We provide an ad hoc approach to that extension in detail and outline two more formal approaches. That extension increases the precision of su...
TL;DR: In this paper, the authors review the history of conservation-value indices and examine attributes of bird communities that make them especially attractive for use in such indices to evaluate and compare sites, and discuss properties of the PIF ranking system that make it an attractive basis for use as species weights for such an index.
Abstract: system of prioritizing bird species of North America (north of Mexico) on the basis of their demography in several categories (Carter et al. 2000). Beissinger et al. (2000) found that to be a sound system, useful for focusing management attention on those species most in need, and proposed a system for using PIF’s categorical scores to derive a priority rank for each species that refl ects its risk of local extirpation. We believe those ranks can be of great utility as species weights in an index to compare bird communities’ “conservation value” as a whole. Here, we review the history of conservation-value indices and examine attributes of bird communities that make them especially attractive for use in such indices to evaluate and compare sites. We then discuss properties of the PIF ranking system that make it an attractive basis for use as species weights for such an index. Finally, we discuss how using this index in concert with more traditional summary statistics can provide additional information on the structure and status of bird communities.
TL;DR: Signatures of past population expansion are evident for some populations of M. flava; expansion is more recent in Moscow, Kursk, Yamal, and Anabar (northeastern group), and older in Tyva and Vyatka (western group).
Abstract: We conducted phylogeographic analyses of Motacilla flava (Yellow Wagtail) and M. citreola (Citrine Wagtail). We analyzed mitochondrial DNA sequences from 167 M. flava specimens obtained from 17 localities throughout Eurasia and Alaska, and 38 specimens of M. citreola obtained from 7 Eurasian localities. Phylogenetic analysis revealed three clades within traditionally recognized M. flava: Europe and southwestern Asia, northeastern Eurasia, and southeastern Asia. Those groups should be considered species, because together they are not monophyletic, and are interspersed with M. citreola, M. cinerea, and M. alba. Motacilla citreola also is paraphyletic, consisting of two species-level groups. Northeastern and southeastern groups of M. flava each appear to be sister taxa to eastern and western groups of M. citreola, respectively. Together those four groups form a clade, whereas the western M. flava group is considerably more distant. Within each of the three groups of M. flava, and the two groups of M...
TL;DR: It is concluded that mice and flying squirrels are predators of canopy nesting passerines, and their potential as nest predators must be considered to understand the consequences of nest predation.
Abstract: Nest predation is the primary cause of nest failure among birds. As such, it has large consequences on avian populations and is believed to be an important force in the evolution of avian life-history traits. Therefore, using a combination of laboratory and field research, we investigated the potential of northern flying squirrels (Glaucomys sabrinus) and two species of deer mice (Peromyscus maniculatus and P. keeni) to be predators on eggs and nestlings of birds, particularly the threatened, canopy nesting Marbled Murrelet (Brachyramphus marmoratus). In captivity, both mice and squirrels atempted to prey on eggs and live nestlings of various sizes. Mice atempted to prey on eggs more than nestlings, were more likely to atack nestlings when hungry than when sated, and were more likely to atack small than large nestlings. Individual flying squirrels varied in their propensity to atack but generally were more likely to atempt to open eggs when hungry than when sated. Opening of eggs by both mice and...