Quantifying community-level host use by generalist brood parasites is important because it provides a measure of the resources that parasites need for reproduction. During the 2002–2007 breeding seasons, we quantified host use by the Brown-headed Cowbird (Molothrus ater) at Konza Prairie Biological Station in northeast Kansas. Overall, 54.4% of nests (n = 2,621) of 22 passerine host species that typically accept parasitic eggs were parasitized, and parasitized nests contained an average of 1.9 ± 1.03 (SD) Brown-headed Cowbird eggs, nestlings, or both. Multiple parasitism was common on the study site in all years: 55.7% of parasitized nests (n = 1,425) received ≥2 Brown-headed Cowbird eggs. The Bell's Vireo (Vireo bellii; 70.5%) and the Dickcissel (Spiza americana; 69.6%) were parasitized at a significantly greater rate than the Red-winged Blackbird (Agelaius phoeniceus, 21.9%); collectively, these three species represented 85.8% of potential host nests found in all years. The host preference of Brown-headed Cowbirds did not appear to shift among the three species and instead they exhibited a consistent preference for Dickcissel nests over the course of the breeding season and among years. Both the rate and the intensity of parasitism on Dickcissels were significantly lower during the present study than in one conducted several decades earlier at the same site. Our results indicate that cowbirds in northeast Kansas differentially parasitize hosts, that most cowbird eggs are laid in the nests of a small number of host species, and that the Dickcissel appears to be preferred over other hosts.

We studied geographic as well as individual variation of songs in five Czech populations of the Tree Pipit (Motacillidae: Anthus trivialis), a passerine bird with a medium-sized syllable repertoire and complex song. We focused on repertoire composition at the level of syllables (the smallest invariant song units) and of structures that are potentially important in recognition among individuals (i.e., bi-syllables, or regular repetitions of two different syllables) and among populations (introductory phrases). We tested the hypotheses that the repertoires reflect local dialects (i.e., different male origins) and that within-site similarities of male repertoires are distance dependent. The populations studied differed significantly in all analyzed characteristics. Male origin explained ∼18% of the variation in individual syllable repertoires. However, no clear within-site geographic structure in repertoire similarity was observed, either between closest neighbors or on larger scales. We observed a tendency for increased syllable sharing among males in a small and dense isolated population, which is consistent with recent studies that suggest the existence of strong effects of habitat fragmentation on geographic patterns of song variation. High individual variation was observed in bi-syllable repertoires, but whether this facilitates individual recognition is unknown and in need of further study.

The study of sexual dichromatism has played an important role in the development and testing of evolutionary theory. However, previous work has often relied on human vision to assess plumage color and contrast, an approach challenged by the finding that dichromatism is often visible to birds but invisible to humans. We explicitly tested whether the use of human vision undermines previous comparative analyses in antbirds (Thamnophilidae). Focusing on a sample of 71 species, we used (1) molecular sequencing of the SWS1 opsin gene to assess spectral sensitivity and (2) spectrophotometry and color discrimination models to compare human and avian perception of dichromatism. We show that antbirds, like the majority of avian families studied to date, are violet-sensitive (VS) rather than ultraviolet-sensitive (UVS). We also demonstrate that species perceived as monochromatic by humans may look dichromatic to antbirds, but that human and avian perceptions of dichromatism are nonetheless positively correlated. To assess whether this relationship validates the assumptions of published comparative analyses, we re-ran the analyses using avian-perceived dichromatism; the results remained qualitatively unchanged. Although it is clear that the use of spectrophotometry and visual models can improve measurements of plumage coloration, we conclude that scores generated from human perception provide a meaningful estimate of sexual dichromatism for the purposes of comparative analyses, at least in antbirds. Furthermore, our results suggest that discrepancies between human and avian perceptions of sexual color differences may be relatively minor in avian families with VS visual systems.

Many North American bird species either accept or reject all Brown-headed Cowbird (Molothrus ater) eggs, but the Common Grackle (Quiscalus quiscula) is unusual in that it rejects a small proportion of experimentally introduced cowbird eggs. We tested whether individual Common Grackles and eight typical rejecter species were consistent in their responses by parasitizing nests a second time after initial cowbird eggs were ejected. We also assessed intraclutch variation in egg appearance in Common Grackles to determine whether it may influence phenotypic plasticity in rejection frequency. Rejections were recorded at 11.9% of 337 experimentally parasitized Common Grackle nests. Only 6 (33.3%) of 18 Common Grackles that ejected initial cowbird eggs also ejected a second experimentally added cowbird egg, however, which suggests that individuals that possess rejection behavior express it only 33.3% of the time. By contrast, the other eight rejecter species rejected between 91% and 100% of initial cowbird eggs (n = 302) and rejected 100% of second cowbird eggs (n = 125). Common Grackles are unique in three ways: they reject eggs at a low frequency, they have a high rate of intraclutch variation in egg appearance, and they exhibit phenotypic plasticity in response to repeated parasitism. It is difficult to ascertain the significance of these attributes, but combined with the fact that Common Grackles are rarely parasitized by cowbirds but may have been parasitized more frequently in the past, they suggest that egg rejection has no current adaptive value and may incur a cost such that Common Grackles may be losing rejection via drift or direct selection.

We studied mating patterns in Saltmarsh Sparrows (Ammodramus caudacutus), a species with no territorial defense, no paternal care, and no pair bonds. Fifty-seven of 60 broods with at least 2 sampled chicks (and all broods that were completely sampled) resulted from multiple mating by females. About one-third of the broods had a different father for each chick, but the most common pattern, found in 36 of 60 nests, was multiple sires, with at least 1 male having sired 2 or more chicks. The level of multiple paternity in Saltmarsh Sparrows may be the highest documented in any bird. Levels of multiple mating increased with population density but not with nesting synchrony. We were able to assign paternity to particular males for about half the 206 chicks that were genotyped. Males sired chicks as far as 1.4 km from their original capture site, and some males sired chicks in multiple nests, separated by up to 0.5 km. We also document a case of 2 females laying eggs in the same nest.

Birds that forage by probing must often use senses other than vision to find their prey. Remote touch is a sense based on the interception of vibrations produced by moving prey in the substrate or on the evaluation of pressure patterns produced by hard-shelled sessile prey. In probing birds, this system is mediated by an organ made up of clusters of mechanoreceptors housed within pits in the bone of the bill-tips. This bill-tip organ was first described in probing shorebirds (Scolopacidae), and more recently in kiwi (Apterygidae). Here, we describe this bill-tip organ in a third family of probing birds, the ibises (Threskiornithidae). We examined the bill morphology of 11 species of ibis from 8 genera. We found bill-tip organs in species in a wide range of habitat types, from predominantly terrestrial to predominantly aquatic, which suggests that ibises may use remote touch when foraging both in water and in granular substrates. Our data imply a link between bill-tip morphology and habitat use—a pattern that we believe warrants further investigation.

The exotic Smooth Cordgrass (Spartina alterniflora) has spread rapidly on the east coast of China over the past three decades and has greatly changed the native saltmarsh vegetation. We conducted bird surveys using mist nets in the exotic Spartina and native Common Reed (Phragmites australis) habitats at Chongming Dongtan of eastern China in the winters of 2004 and 2005. We related bird capture rates to habitat type (Phragmites or Spartina habitat), habitat structure (plant height and density), and food availability (densities of seeds and arthropods). The Spartina habitat was composed of shorter and denser vegetation and provided fewer food resources for birds than the Phragmites habitat. Bird capture rate was lower in Spartina, negatively related to plant density in the Spartina habitat, and positively correlated with overall arthropod abundance and plant height. Food resources consumed by birds were similar to those found in Phragmites habitat, irrespective of capture location. Our results suggest that the alteration of habitat structure and reduction in food resources are probably the proximate causes of lower avian species richness and relative abundance in the exotic Spartina than in the Phragmites habitat at Chongming Dongtan.

Although conservation theory argues for large habitat patches, most grasslands in the Midwest are small. To assess the influence of patch size and proximity to edges on nest survival, we monitored 816 nests of two grassland-nesting species, Dickcissel (Spiza americana) and Eastern Meadowlark (Sturnella magna), from 1996 to 2000 in a network of grasslands (3–142 ha) surrounded by cropland and small patches (<1 ha) of woody vegetation in southeastern Illinois. In this grassland-agriculture matrix, small patch size and proximity to cropland edges did not negatively affect nesting success of these two grassland species of management concern that commonly occur in small patches. Although larger grasslands are necessary to attract area-sensitive species, this work demonstrates the importance of even small grassland patches for nesting habitat in grassland birds. The landscape-scale density of grassland patches in this area may also contribute to the nesting success of these birds. Our results suggest that loss of small grassland patches would have a direct negative effect on population fecundity and an unknown impact through cumulative landscape effects.

The Araripe Manakin (Passeriformes: Pipridae: Antilophia bokermanni) is the most threatened passeriform species and is classified as critically endangered. With an estimated population of only 800 individuals, this species is endemic to a small area (∼30 km2) of forest on the slopes of the Araripe Plateau in northeastern Brazil. The urgent need to implement an effective conservation program for the Araripe Manakin has stimulated intensive research into various aspects of its biology. We sequenced a segment of the mtDNA between the genes ND6 and 12S rDNA, which includes a pseudo-control region. This region was analyzed in 30 specimens of A. bokermanni with the aim of measuring intraspecific genetic diversity and population structure. Although the segment's position is the same as described in other bird species, A. bokermanni differs in some aspects, such as its length of 200 base pairs and the absence of indels or tandem repeats. Our analysis provides no evidence of population substructuring or a history of population expansion. The species' genetic variability is slightly reduced in comparison with its sister species A. galeata, but their similarity indicates a relatively recent process of separation.

Endangered species are sensitive to the genetic effects of fragmentation, small population size, and inbreeding, so effective management requires a thorough understanding of their breeding systems and genetic diversity. The Greater Sage-Grouse (Centrocercus urophasianus) is a lekking species that has declined by 66–92% during the past 35 years in Alberta. Our goals were to assess the genetic diversity of Greater Sage-Grouse in Alberta and to determine the degree of sex-specific relatedness within and among leks. Six hundred and four individuals sampled in 1998–2007 were genotyped at 13 microsatellite loci. Levels of genetic diversity were high, with the exception of one recently founded lek, and did not change over time. Overall, we did not observe isolation-by-distance among leks, and most leks were not differentiated from one another, which suggests that gene flow occurs across the study area. Males and females exhibited similar patterns of isolation-by-distance, so dispersal was not sex-specific. Overall relatedness was close to zero for both sexes at the level of the province, lek, and year, which suggests that neither sex forms strong kin associations. However, we found relatedness within leks at the year level to be greater than zero, which indicates interannual variation. We also found no evidence that Greater Sage-Grouse follow the typical avian pattern of male philopatry. Although the species is endangered in Alberta and occurs in fragmented habitat, it has maintained genetic diversity and connectivity.

Habitat selection is a hierarchical process that proceeds from broad to fine spatial scales. Failure to account for spatial scale in studies of habitat selection may result in an incomplete understanding of key habitat characteristics. For juvenile songbirds, postfledging habitat may be important for migratory preparation and survival; however, there is currently little information regarding habitat associations during this period. We used radiotelemetry to investigate habitat associations at fine and broad spatial scales in juvenile Yellow-rumped Warblers (Dendroica coronata) and Blackpoll Warblers (D. striata) in a managed boreal forest in northwestern Newfoundland. At the local scale, both species were associated with locations characterized by dense vegetative cover, and Blackpoll Warblers were also associated with locations characterized by high amounts of coarse woody debris. At broader extents, Yellow-rumped Warblers were associated with patches situated downslope of their previous location, as well as patches surrounded by low amounts of clearcut land cover at the 115-m scale and patches with high foliage density during 2006. Unlike Yellow-rumped Warblers, Blackpoll Warblers were more likely to be observed in patches surrounded by high amounts of clearcut land cover at the 115-m scale and were sensitive to clearcut land cover at the 1,250-m scale. Our results demonstrate the importance of spatial scale in studies of habitat association; given interspecific differences in response to clearcut land cover, they also suggest that a general management strategy for songbirds with respect to clearcut land cover in the boreal forest may remain elusive.

Although postfledging movement patterns have been described for several species, the factors that influence these movements remain unclear. We quantified natal home-range size and dispersal patterns of two songbird species and evaluated the relative importance of nestling condition, brood size, predation risk, and habitat structure on postfledging movements. We radiotagged and tracked 51 Ovenbirds (Seiurus aurocapilla) and 60 Worm-eating Warblers (Helmitheros vermivorum) between 2004 and 2007. For each radiotagged bird, we calculated distances from daily locations to the original nest, successive distances between daily locations, mean dispersal distance from the natal area, number of days before dispersal, and natal home-range size. We built and ranked alternative models to represent mechanisms that potentially influence movements 2 days after fledging. The natal home-range size of Worm-eating Warblers (10.4 ha ± 1.50 [SE]) was twice that of Ovenbirds (5.0 ha ± 0.56). Fledgling age was positively correlated with the distance moved from the nest and between daily locations. Relative body mass at the time of fledging was positively associated with the mean distance between daily locations 2 days after fledging. This research generated two important insights into postfledging ecology: (1) that conditions experienced by birds in the nest may ultimately facilitate or constrain their ability to locate suitable habitat, which is known to influence fledgling survival; and (2) that large natal home ranges and relatively long dispersal distances away from the natal area may contribute to area sensitivity in songbirds.

Delayed natal dispersal occurs in many tropical and southern temperate species. In these species, juveniles remain with their parents on natal territories for periods beyond the age of nutritional independence, in contrast to juveniles of northern temperate species, in which prompt dispersal is more typical. Despite its prominence in the life history of tropical and southern temperate birds and its importance in setting the stage for prolonged social interactions among kin, detailed knowledge about delayed dispersal in most species that inhabit these regions is lacking. We describe patterns of delayed dispersal, territory acquisition, and natal dispersal distances in a Neotropical species, the Buff-breasted Wren (Thryothorus leucotis). Male and female juveniles were both philopatric to natal territories and delayed dispersal for an average of 10 months after fledging. Most juveniles were no longer present on natal territories when their parents began to breed the following year, so opportunities for cooperative breeding were rare. Juveniles that stayed longer on natal territories were more likely to recruit into the local breeding population than individuals that dispersed earlier, and approximately two-thirds of juveniles that acquired territories within the study area shared at least one territorial boundary with kin. By remaining on natal territories for prolonged periods and acquiring territories near their parents, juvenile Buff-breasted Wrens may avoid potential costs associated with floating and may benefit from extended opportunities to interact with kin.

Models for estimating survival probability of nests and young have changed dramatically since the development of the Mayfield method. Improvements in software and a steady increase in computing power have allowed more complexity and realism in these models, allowing researchers to provide better estimates of survival and to relate survival rates to relevant covariates. However, many current analysis methods utilize fixed-effects models with the implicit assumption that the covariates explain all of the variation in the data, other than random variation within a specified family of distributions. This is generally a strong assumption, and, in the presence of heterogeneity and lack of independence, these estimates have been shown to be negatively biased. Others have begun to explore random-effects models for these situations, but a readily applicable Bayesian approach has been lacking. We present a general Bayesian modeling framework appropriate for survival of both nests and young that simultaneously allows for the inclusion of individual covariates and random effects and provides a measure of goodness-of-fit. We used previously published data on survival of Common Goldeneye (Bucephala clangula) ducklings in interior Alaska and on nest survival in three species of prairie-nesting ducks that nested in the Missouri Coteau region of North Dakota to demonstrate this approach. The inclusion of a brood-level random effect in the Common Goldeneye example increased point estimates and credible interval [CI] coverage from 0.62 (95% CI: 0.49–0.73) and 0.66 (95% CI: 0.58–0.74) for 2002 and 2003, respectively, to 0.69 (95% CI: 0.42–0.88) and 0.74 (95% CI: 0.57–0.88) for 2002 and 2003, respectively.

The North American Breeding Bird Survey (BBS) is an annual roadside survey used to estimate population change in >420 species of birds that breed in North America. Roadside sampling has been criticized, in part because traffic noise can interfere with bird counts. Since 1997, data have been collected on the numbers of vehicles that pass during counts at each stop. We assessed the effect of traffic by modeling total vehicles as a covariate of counts in hierarchical Poisson regression models used to estimate population change. We selected species for analysis that represent birds detected at low and high abundance and birds with songs of low and high frequencies. Increases in vehicle counts were associated with decreases in bird counts in most of the species examined. The size and direction of these effects remained relatively constant between two alternative models that we analyzed. Although this analysis indicated only a small effect of incorporating traffic effects when modeling roadside counts of birds, we suggest that continued evaluation of changes in traffic at BBS stops should be a component of future BBS analyses.

Each year, hundreds of thousands of shorebirds use Delaware Bay, on the northeast coast of the United States, as a final stopover before migration to breeding areas. The bay provides them with abundant Horseshoe Crab (Limulus polyphemus) eggs, which they use to gain the fat stores necessary for continued migration and subsequent survival on the breeding grounds. However, abundant food attracts dense mixed-species flocks, which may facilitate pathogen transmission, and migration itself may suppress immune defense. Despite the potential importance of disease risk and immune function during migration, little is known about how immune function changes during stopover in migratory shorebirds. To examine this, we measured constitutive immune function in Red Knots (Calidris canutus rufa) during stopover in Delaware Bay. We found lower total leukocyte, lymphocyte, and monocyte concentrations, complement-mediated lysis, and haptoglobin activity in birds recovering protein after migration than in birds storing fat to fuel subsequent flight. We discuss two possible reasons for this result. First, fueling birds may have an increased rate of infection or may be bolstering immune defense in response to high antigen exposure. Second, recovering birds may be immuno-compromised because of the physical strain of migratory flight or as a result of adaptive tradeoffs between immune function and migration.

Abandonment was the most frequent cause of nesting failure in Great Lakes Piping Plovers (Charadrius melodus) during 1993–2007, and observations of color-banded adults suggested that most abandonments involved disappearance of attendant adults rather than behavioral decisions by adults to desert their nests. The purpose of our study was to integrate nest-monitoring histories with mark—resighting analyses to determine whether nest abandonment indicated adult mortality or nest desertion. Nesting Piping Plovers had extremely high within-year resighting probabilities (10-day mean p = 0.908 ± 0.025 [SE] ), and cumulative probabilities of being detected approached 1 for individuals that were present on the breeding grounds for ≥20 days post-abandonment. These observations suggested that desertion would be readily identified unless Piping Plovers left the monitoring areas immediately after deserting their nests. None of the 31 that disappeared (as indicated by nest-monitoring histories) was ever observed again, and an among-year mark—resighting analysis suggested that all had died. From 2002 to 2007, annual mortality associated with disappearances averaged 5.7% of the marked population. Disappearances occurred primarily from 16 May to 19 June, were more common among females, involved individuals that were older than average, and were most frequently attributed to predation by Merlins (Falco columbarius). Our results reveal that most early-season nest abandonment in Piping Plovers was attributable to the death of attendant adults. We believe that this phenomenon may be widespread among other species of birds in which adults are vulnerable to mortality during nesting.

We compared the pronounced geographic pattern in the recolonization of Britain by the Eurasian Sparrowhawk (Accipiter nisus) from 1970 onward with the spatiotemporal pattern among House Sparrow (Passer domesticus) populations over the same period, using data on the occurrence of both species at garden feeding stations. Using a simulation of House Sparrow population trends based on a logistic model that incorporated a predation index derived from Eurasian Sparrowhawk incidence functions, we generated a close approximation to the unique trajectories among House Sparrow populations in rural and urban sites in different regions of Britain. We carried out further comparisons using two contrasting methods that focused solely on temporal patterns. We used estimates of the varying date of Eurasian Sparrowhawk recolonization at different sites to derive time variables in relation to recolonization date. One such relative time variable proved to be a better predictor of House Sparrow numbers than chronological time; it indicated that House Sparrow numbers were generally stable or increasing prior to recolonization by Eurasian Sparrowhawks but declined continuously afterward. We also detected a significantly greater decrease in House Sparrow numbers when Eurasian Sparrowhawks were present using a method that compared annual changes in the abundance of prey species in the presence or absence of a predator. On the basis of these results, we argue that predation by Eurasian Sparrowhawks may be a sufficient explanation for the decline in House Sparrows in Britain. We also argue that urban House Sparrow populations' long-term release from predator pressure made them especially vulnerable when urban habitats were colonized by Eurasian Sparrowhawks.

Resident or short-distance migrant birds that occupy urban habitats are known to breed earlier than nearby rural populations, but similar data on long-distance tropical migrants are lacking. To understand the relationship between urbanization and reproductive phenology of a tropical migratory bird species, we (1) described variation in patterns and consequences of breeding phenology across an urban-to-rural gradient and (2) assessed underlying reasons why phenology may be related to urbanization. We studied Acadian Flycatchers (Empidonax virescens) between 2001 and 2007 in 35 forests spanning an urban-to-rural gradient in central Ohio. The general pattern of breeding phenology was opposite of that described for most resident and short-distance migrant birds. At higher levels of urbanization, site arrival dates and clutch initiations were later and cessation of breeding was earlier than in forests of more rural landscapes. The phenological shifts reduced the length of the nesting season in urban landscapes, with the result that birds in more urban landscapes initiated fewer nests and fledged fewer young than their rural-breeding counterparts. Underlying causes of phenological differences are less clear. One possibility supported by our data is that urban forests are less desirable and selected later by smaller females, which initiated first clutches later in the nesting season than larger females. This study provides the first evidence that urbanization is associated with attenuated nesting seasons for tropical migratory birds and that this shift in breeding phenology may have reproductive consequences.

We investigated the phylogenetic relationships of Campylorhamphus pucherani using DNA sequences from three mitochondrial genes and a nuclear intron, as well as 84 morphological characters from the skeleton, the integument, and the musculature. The molecular phylogeny indicated that C. pucherani is not part of Campylorhamphus; instead, it is the sister species to Drymornis bridgesii, in a clade that also contains Lepidocolaptes. The morphological phylogeny also placed C. pucherani in a clade that contains Drymornis and Lepidocolaptes. Using a morphometric analysis of size and shape diversity, we demonstrated that the inclusion of C. pucherani in Drymornis would create an excessively heterogeneous genus compared with other dendrocolaptine genera. Because no generic name is available for C. pucherani, we describe the new genus Drymotoxeres for this species.

We estimated phylogenetic relationships among all 15 extant species of cranes in the gruiform family Gruidae from complete sequences of their mitochondrial genomes. The gene order of crane mitochondrial genomes corresponds to that of the chicken and present few structural novelties compared with previously described birds. Sequences of the control region, particularly domains I and III, are highly divergent among species and include tandem repeats, duplications, and numerous indels. Phylogenetic analyses confirmed the well-established, reciprocal monophyly of clades Balearicinae (crowned cranes) and Gruinae (anatomically derived cranes), as well as previously identified lineages within Gruinae: Leucogeranus and the species groups Anthropoides, Canadensis, Antigone, and Americana. As in previous molecular phylogenies, Leucogeranus is resolved as sister to all other gruines. In addition, the Sandhill Crane (Grus canadensis) is resolved as sister to the Antigone species group, resulting in a Pacific Rim clade that has not previously been suggested. Only relationships among the Anthropoides, Americana, and Pacific Rim groups remain unresolved in our analyses. The crane fossil record provides reasonable calibration points for the most recent common ancestor of Gruinae (Middle Miocene) and the minimum age of Grus americana (Late Pliocene). Bayesian estimates of divergence dates from mitochondrial DNA sequences suggest that balearicines and gruines separated in the late Oligocene and that radiations of living species within these clades took place in the Neogene.

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.