Studies of sexual dimorphism often focus on the evolution of elaborate male traits, whereas the evolution of elaborate females has been largely ignored. Yet a phylogenetic perspective suggests that changes in either male or female traits may lead to the evolution of sexual dimorphism. Furthermore, changes in the degree of sexual dichromatism can be caused by gains or losses of elaboration. One common form of elaboration found throughout the animal kingdom is the use of highly saturated and contrasting colors. To investigate further the evolution of female elaboration and sexual dichromatism, we took quantitative measurements of color from New World orioles (Icterus spp.) and then used ancestral-state reconstruction to infer evolutionary changes in male and female elaboration. Our findings suggest that male elaboration is ancestral and strongly conserved but that female elaboration has changed repeatedly, especially through the loss of saturation and contrast. Thus, changes in female—rather than male—color appear to lead to the evolution of sexual dichromatism in orioles. These repeated gains of strong sexual dichromatism through the loss of female elaboration were supported using multiple methods of character coding and reconstruction. Our phylogenetic results suggest that studies of sexual dichromatism cannot assume that color dimorphism arises through increased male elaboration. These findings have important implications for future studies investigating the ultimate causes of sexual dichromatism.

Several recent studies have investigated how different proximate mechanisms of color production contribute to sexual dichromatism. These studies suggest that carotenoid pigments—which are frequently subject to sexual selection—are more strongly associated with sexual dichromatism than melanins. This reasoning implicitly assumes that increased male elaboration leads to sexual dichromatism. However, sexual dichromatism can be generated through multiple evolutionary pathways, including decreases in female elaboration. We examined whether evolutionary changes in carotenoid- and melanin-based plumage were correlated within New World orioles (Icterus spp.), a genus in which male elaboration is ancestral and only female elaboration varies. We found a significant correlation between evolutionary changes in the degree of carotenoid and eumelanin sexual dichromatism. These findings differ from those of previous comparative studies and suggest the possibility of interesting differences when different evolutionary pathways—such as changes in male versus female coloration—lead to sexual dichromatism.

African populations of the Village Weaver (Ploceus cucullatus) are subject to brood parasitism by the egg-mimicking Diederik Cuckoo (Chrysococcyx caprius), which has resulted in high variation in egg color between individuals. Considering the nesting environment of the Village Weaver and the putative pre-parasitism ancestral egg color, I hypothesize that blue-green pigment may protect Village Weaver embryos from solar radiation. On this basis, more intense (more chromatic) blue-green egg colors may have evolved by natural selection in Village Weavers in the absence of Diederik Cuckoos. Moreover, even in African populations that are parasitized, Village Weaver eggs may have diverged in accordance with nesting light environments. In accordance with the proposed hypothesis, over the past two centuries two introduced populations have evolved more intense blue-green egg colors compared with their source populations. Two African source populations also differ from each other in the predicted direction, the population with the sunnier nesting climate having more intensely blue-green eggs. These results suggest that upon relaxation of brood parasitism by an egg mimic, Village Weaver eggs may adapt to solar radiation.

Museum specimens are valuable for studies of plumage color in birds, but feather color may fade over time and not accurately reflect the colors of live birds. In particular, it has been suggested that ultraviolet (UV) color may be more susceptible to degradation than human-visible colors. We used a reflectance spectrophotometer to measure feather color in five species of passerines for which museum specimens were collected consistently over the past 100 years. We found that the feather colors of museum specimens collected within the past 50 years were related closely to the feather colors of live birds. In fact, over a wide range of different colors, we found little change in color measurements for recent (<50 years old) specimens. Furthermore, UV color was not affected more severely by fading than human-visible colors when we confined our analyses to recent specimens. These results provide strong support for the continued use of museum specimens to examine coloration in birds, provided that the specimens were collected relatively recently.

We analyzed the seasonality of molt of African Penguins (Spheniscus demersus) in adult plumage and used information derived from banded individuals to examine the relationship between age, breeding status, and timing of molt in Namibia. Molt seasonality was bimodal, with a major molt peak in the austral autumn and a minor peak in midsummer. African Penguins younger than four years—and, therefore, unlikely to be sexually mature—molted in early January, at the same time as juvenile African Penguins. Birds aged between four and six years molted either in summer or autumn and were likely to be individuals making the transition from nonbreeder to breeder. African Penguins older than six years, considered to be breeders, molted, on average, in early May. Most birds that had been recorded breeding within 12 months of molt molted between March and May. Summer breeding in Namibia appears to force breeders to delay molt until autumn. There was individual variation in molt seasonality that we could not explain by age alone. Estimates of the proportion of potential breeders in the population derived from molt phenology and from the molt histories of banded, known-age individuals were likely to be underestimates and suggested that some adults of breeding age defer breeding.

Brood parasitism and predation are two factors that limit seasonal fecundity in grassland songbirds. We removed Brown-headed Cowbirds (Molothrus ater) in a switchback experiment to examine the effects of brood parasitism and nest predation on the productivity of Dickcissels (Spiza americana). Nesting Dickcissels were monitored at four study plots in northeast Kansas in a two-year study. Brown-headed Cowbirds were captured with drop-in traps at two removal plots, two unmanipulated plots were reference plots, and treatments were reversed between years. To evaluate the effect of Brown-headed Cowbird removals, we compared the percentage of nests parasitized, rates of multiple parasitism, clutch size, daily nest survival rates, and overall productivity per nest between removal and reference plots. Removals of Brown-headed Cowbirds successfully reduced the probability of parasitism and rates of multiple parasitism, but only in one of two years. Brown-headed Cowbirds did not appear to contribute to nest losses, given that few nests were abandoned because of cowbird activity and that the probabilities of nest parasitism and nest survival declined simultaneously over the breeding season. Overall, nest productivity showed no difference between treatments in either year, despite reduced rates of parasitism at removal plots in 2004. High rates of nest predation minimized the potential benefits of Brown-headed Cowbird removals for increasing productivity of Dickcissels. Our results demonstrate that removals can reduce parasitism levels but that the success of removal programs may vary annually, particularly in regions where Brown-headed Cowbirds and nest predators are abundant. Management actions that minimize parasitism and predation by modifying habitat structure may provide better alternatives to programs based on removals.

Birds can save distance and time on their migratory journeys by following great circles rather than rhumblines, but great-circle routes require more complex orientation with changing courses. Flight directions at different places along the route and in relation to the destination can be used to test whether birds migrate along great circles or rhumblines. Such data have indicated great-circle migration among shorebirds at high latitudes, but no critical tests have been made for passerines. Using tracking radar on board the icebreaker Oden in August 2005, we recorded westerly flight directions of passerine migrants over the Chukchi Sea. The main sector of migratory directions was 237–311° centered on a mean heading direction of 274°. The most likely species to participate in this westward trans-Beringia migration, mainly departing from Alaska, were Eastern Yellow Wagtail (Motacilla tschutschensis), Arctic Warbler (Phylloscopus borealis kennicotti), Northern Wheatear (Oenanthe oenanthe), and Bluethroat (Luscinia svecica); all except the Bluethroat were recorded from the ship. Observed flight directions agreed with predicted great-circle courses but not with rhumbline courses for three of these four species with winter quarters in Southeast Asia; no definite conclusion could be drawn for the Northern Wheatear (wintering in East Africa). These results support great-circle migration among passerines traveling between Alaska and Old World winter quarters, though the long-distance precision and orientation mechanisms are still unknown. The relative importance of different evolutionary causes—such as circumvention of geographic barriers, retracing of ancient colonization ways, or distance reduction by great-circle migration—to complex bird migration routes with changing courses remains to be understood.

Western Scrub-Jays (Aphelocoma californica) range throughout the western United States and Mexico and exhibit substantial geographic variation in morphology and behavior. Western Scrub-Jays are a polytypic species complex with three distinct groups (californica, woodhouseii, and sumichrasti) associated with geography and distinguished by morphology, genetics, and behavior. Until recently, the Island Scrub-Jay (A. insularis) and the Florida Scrub-Jay (A. coerulescens) were considered subspecies within the Western Scrub-Jay complex. We analyzed mitochondrial DNA sequences (control region I) to reveal the phylogenetic relationships within Western Scrub-Jays and used maximum likelihood, a Bayesian approach, and a relaxed phylogenetic approach to construct phylogenies. In addition, we used several methods to estimate divergence time between clades. Our results reveal that the interior woodhouseii group, which contains the sumichrasti subclade, and the coastal californica group have had a long and independent evolutionary history. However, samples from a contact zone in western Nevada were genetically woodhouseii and morphologically californica. Island Scrub-Jays evolved from the coastal californica, which makes Western Scrub-Jays paraphyletic with respect to Island Scrub-Jays. To solve the problem of paraphyly and to more accurately define the diversity that exists within Western Scrub-Jays, we suggest splitting Western Scrub-Jays into two or three species, California Scrub-Jay (A. californica), Woodhouse's Scrub-Jay (A. woodhouseii), and, potentially, Sumichrast's Scrub-Jay (A. sumichrasti).

We used capture–mark–recapture (or re-encounter) analysis of a metapopulation to estimate the probability of survival, re-encounter, and dispersal of Arctic Terns (Sterna paradisaea) nesting in the Gulf of Maine and the Bay of Fundy. Before our study, there were only a few anecdotal accounts of breeding dispersal, and the only estimates of survival for this species were calculated in the 1950s and 1960s in the United Kingdom, using return rates unadjusted for recapture probability. Approximately 45% of the North American breeding population nests in the Gulf of Maine region; 95% of these nest on the four islands studied. Re-encounter observations of 2,295 adult Arctic Terns banded on these four key islands were collected from 1999 to 2005. An information-theoretic approach was used to determine the model best describing survival and movement patterns. Models using the program M-SURGE suggested that the apparent survival of adult Arctic Terns was colony- and year-specific, ranging from 0.704 to 0.960 when transient individuals were accounted for. Re-encounter probabilities were generally low, ranging from 0.12 to 0.74, depending on colony and year. Fidelity to previous breeding colonies was high; estimated probability of movement among colonies ranged from 0.000 to 0.015. Breeding dispersal was negatively correlated with distances among islands, but not with colony size. There was no difference between male and female Arctic Terns in survival, re-encounter, or breeding dispersal.

The disturbance associated with nest monitoring raises concerns about the validity of the estimated nest success and the well-being of the populations under study. Observer activity may attract or deter predators to or from bird nests, thus decreasing or increasing nest success. Results of previous studies related nest success to frequency of nest visits or estimated survival over rechecking intervals of different length. Such studies usually cannot reveal the underlying mechanism through which predation rate is influenced, because the timing of predation remains unknown. I measured, using data loggers, the exact survival times of 747 nests of 11 songbird species in fragmented woodland in the Czech Republic in 2001–2003 and analyzed the temporal relationship between predation and observer visits. I found only a short-term observer effect that lowered the hazard of predation during 2 h after a visit but did not appreciably affect the overall nest success. The timing of nest visits and the short duration of the effect imply that predators were deterred from the nests directly by the observer's presence, rather than by long-lasting cues (scent trails, damage to vegetation), and that diurnal predators (mainly corvids) responded to observer presence. This effect was consistent across years but differed between species groups. Deterrence of avian predators was profitable for a heterogeneous "warbler" group of species with limited nest-defense ability (model-averaged hazard ratio: 0.38; 95% confidence interval: 0.12–1.25), but it had little effect on thrushes (Turdus spp.; 1.01; 0.28–3.68). I support the view that predation on songbird nests is not increased by repeated observer visits, especially in situations where nest densities and background human disturbance are high.

The yellow-breasted meadowlarks have endured more than a century of debate over species limits and patterns of diversity, ending with the current recognition of two species, the Eastern and Western meadowlarks (Sturnella magna and S. neglecta), by most authorities. Recently, it has been suggested that a form of the Eastern Meadowlark from the desert Southwest of the United States and northern Mexico is a distinct taxon, Lilian's Meadowlark (S. lilianae). We gathered sequence data from the mitochondrial genes cytochrome b and ND2 and from an intron of the sex-linked gene aconitase 1, from samples of all three forms from across their ranges. By genealogical concordance, these data strongly support the existence of three differentiated, historically isolated lineages. We recommend species recognition for S. lilianae (including the Mexican form auropectoralis), and note that its distributional limits in Mexico require clarification. Finally, we note that Z-linked nuclear markers may be particularly useful for lineage delimitation and phylogeny estimation in groups characterized by large variance in male reproductive success.

Habitat selection by migratory bird species affects their fitness. Studies of populations with marked individuals of known reproductive performance provide the greatest insight on the relationship between a species and the range of habitats it occupies. Canada Warblers (Wilsonia canadensis) have not been intensively investigated at the population level, despite significant regional declines in their numbers over the past 40 years (e.g., 4.6% year⁻¹ in New Hampshire). We mapped 92 male territories over four years and quantified habitat structure and habitat composition for territories and nonterritory areas. Analyses revealed more shrubs (stems and foliage), more perch trees, and lower canopy height on territories. Birds returned at an average rate of 52.0 ± 2.96% (SE) and exhibited average between-year shifts of 32 m in territory locations. Over the four years, males had high pairing success (91.0 ± 5.61%). Three-quarters of paired males fledged at least one young. Pairing and fledging success did not influence site fidelity. Paired males had more shrub stems and song-perch trees. Territories of earlier-arriving males had more shrub stems. The high proportion of males pairing and successfully fledging young, together with the high average return rates, indicate that areas with dense subcanopy vegetation constitute prime Canada Warbler breeding habitat in New Hampshire. Timber harvest practices that result in high shrub density and residual standing trees, such as deferment or two-age harvest, have the potential to slow Canada Warbler population declines, but only if they are widely applied in forest management.

Responses of parent birds to changes in demands by their offspring have typically been investigated by manipulating brood size and testing for altered patterns of provisioning. We applied an alternative method to breeding pairs of American Kestrels (Falco sparverius) by modifying the duration of their nesting periods. Rather than focusing on how hard parents can work on any given day, this novel approach tests how long they can sustain the stress of provisioning and the associated behavioral consequences. We manipulated nesting periods by exchanging nearly fledged young at the age of 20 days with offspring from other nests that were 10 days old. We found that males provisioned their second foster broods at rates similar to those for their original broods. By contrast, females brooded offspring in second foster nests less and also delivered less food to them. As a consequence, male offspring in second nests gained less mass than those in first nests, and nestlings of both sexes had reduced feather growth in second nests. Our results, together with those from previous investigations on parental behavior of American Kestrels, suggest that investment strategies of males and females are determined by different proximate mechanisms. Males appear to invest according to the number of young in their nests, whereas females appear to fine-tune their investment according to variation in attributes of individual offspring, such as nutritional condition or reproductive value. We further suggest that female parents invested less in second foster broods because they are more susceptible to costs of reproduction than males.

Chick-a-dee calls are common vocal signals in chickadees (Poecile spp.) that function in social organization. Earlier work indicated that the call is a structurally complex vocal system, in that it is open-ended and, theoretically, could convey a large amount of information. However, little quantitative empirical work has addressed whether signalers actually produce distinct chick-a-dee calls in different environmental or behavioral contexts. I tested this question in an eastern population of Carolina Chickadees (Poecile carolinensis). Calls were recorded from free-living birds, and contextual variables were noted at the time of call production. The structure of the chick-a-dee call—the average number of note types used in calls and the different categories of note composition used commonly by birds—was associated with a diverse set of variables, including the proximity of the signaler to the ground, the signaler's flight behavior and local population, and the presence of an avian predator. These results suggest that a receiver could gain considerable information about the signaler and its immediate environment from the different uses of note types in a signaler's calls. Furthermore, these findings support the notion, raised in earlier studies, that the chick-a-dee call is structurally and informationally complex.

One long-standing ornithological paradigm holds that song learning in oscine songbirds has a cultural component, whereas suboscine songbirds inherit songs genetically. Recent studies reveal that suboscine song may be more variable and complex than previously realized. Several suboscine species show marked individual variation in their songs—variation that may play a role in individual recognition and neighbor–stranger discrimination—and a few suboscine species show indications of song learning. We investigated individual variation in the vocalizations of a suboscine passerine, the Screaming Piha (Lipaugus vociferans), from recordings of 26 males at four lek sites along the Tambopata River in Peru. Male Screaming Piha songs consist of quiet introductory syllables followed by two explosively loud syllables that sound like an emphatic pee haw. We used three complementary methods to examine variation in song characteristics. Spectrogram cross-correlation revealed significant consistency within individual males and variability among males. Analysis of fine structural characteristics revealed that all measured song features were significantly less variable within individuals than among individuals. Canonical discriminant analysis based on these 13 song features correctly classified 93.2% of songs by individual and 76.4% of songs by lek site. Our results indicate that there is sufficient consistency in song features within males and sufficient variation among males for identification of individuals on the basis of songs and, to a lesser extent, that song features vary with the lek site of the singer. We conclude that Screaming Pihas sing songs that are individually distinctive and bear a lek signature.

Parasite defense is costly, and the detrimental effects of parasites, which can be measured in terms of parasite virulence, are thought to be influenced by the resources available to the host and, ultimately, by environmental conditions. Hence, if conditions are good, hosts can tolerate a certain number of parasites without suffering severe effects. In addition, the presence of other parasites can influence the virulence of a focal parasite either positively or negatively. We tested whether an experimental tick infestation reduced nestling performance in Great Tits (Parus major) and whether the effect was altered by a maternal response induced by Hen Fleas (Ceratophyllus gallinae) that is known to protect nestlings against flea infestations (i.e., we tested whether one parasite can alter the virulence of another parasite across host generations). We induced the maternal effect by experimentally infesting half the birds' nests with fleas during egg laying. After hatching, nestlings were cross-fostered into broods that then contained both nestlings with and without the maternal effect. Half of these broods were infested with five tick larvae per nestling. This resulted in tick infestation levels similar to levels found in natural populations. The tick infestation did not affect nestling mass, tarsus length, or time until fledging. Thus, an effect of the flea-induced maternal effect on tick virulence was not detectable. From these results, we concluded that either tick larvae do not affect nestlings, or nestlings or their parents can compensate for the negative consequences of tick infestations in numbers similar to those that occur in nature.

Populations occupying "sink" habitats can persist if productive local subpopulations exist, if immigrants rescue the population, or if both processes occur. We tested these hypotheses by combining capture–mark–recapture data and recruit origin assignments obtained from feather stable-isotope values from a local Mallard (Anas platyrhynchos) population breeding near Minnedosa, Manitoba, during 2002–2005. Effects important to population growth rates included female nest location (nest tunnel vs. non-tunnel) and recruitment of yearling females originating locally or from nearby parkland areas rather than from more distant regions. Population growth rates of tunnel-nesting females (mean = 1.21 ± 0.22 [SD], n = 3 years) annually exceeded population stability, primarily because the apparent annual survival rate was consistently >0.75. Population growth rates for non-tunnel females (0.90 ± 0.17, n = 3 years) varied annually in response to recruitment rates of yearling females from Aspen Parkland areas; there was little support for models that represented population rescue by yearling immigrants produced in the U.S. Prairie Pothole and Canadian Boreal Forest regions. Elevated apparent survival rates of adult females using nest-tunnel locations and fine-scale dispersal of yearling females recruited from local subpopulations or nearby source populations are responsible for sustaining local Mallard levels near Minnedosa. This is the first study to demonstrate clearly the value of nest tunnels for increasing adult female survival and productivity of Mallards at a local scale. Integrating mark–recapture and isotopic information may be valuable in testing ecological and management hypotheses about dispersal and demographic processes, as well as in determining the value of nest-structure programs for avian conservation.

The North American Breeding Bird Survey (BBS) provides a widely used source of information on changes in bird population abundance based on data obtained for >50 years by 3-min point counts (Sauer et al. 2005). Rosenberg and Blancher (2005) provided a method that purports to convert BBS data into estimates of absolute abundance. To test this method, we compiled detection efficiencies using BBS protocol at five stations in southern New York where territories of most breeding birds were known. Following the Rosenberg-Blancher method, we assigned species to distance categories, within which it is assumed that the equivalent of 100% of a species will be detected. Field results show that individual detection efficiencies varied from 3% to 49% among 29 species. These values are similar to results from other field studies. Most males did not sing within a 3-min count during June, and the detection distances assumed by the method are much too high. We recommend that conservation priorities of the Landbird Conservation Plan by Partners in Flight should not be based on population estimates derived by such an erroneous method.

We describe the occurrence and behavior of Razorbills (Alca torda) visiting Coats Island, Northern Hudson Bay, an area where sea-ice cover in summer has been much reduced since the mid-1990s. Coats Island is 300 km from the previous most-westerly breeding site for the species and nearly 2,000 km from the nearest large colony, in Newfoundland and Labrador. Razorbills appeared at Coats Island coincidentally with an increase in the delivery of Capelin (Mallotus villosus) and sand lance (Ammodytes spp.) to Thick-billed Murre (Uria lomvia) nestlings at the same site and disappeared when sand lance also disappeared. Razorbill populations are expanding in eastern North America, and this expansion may partly account for their dispersal. The ability of Razorbills to track changes in a preferred prey item well outside the boundary of their normal range suggests that this species is capable of adapting rapidly to climate change.

The health state of nestlings can be a useful bioindicator of the quality of the environment in which they are reared, but, to enable detection of responses to environmental change, the variation of health parameters under natural conditions should be evaluated. We describe the variation of morphological, biochemical, and hematological variables in relation to time of sampling, hatching date, brood size and type, and year in nestlings of two populations of Great Tits (Parus major) in Choupal, Portugal, and Wytham, United Kingdom. The influence of these health variables on nestlings' survival to first winter and recruitment into the breeding population was assessed in Wytham. Variation in plasma protein, total plasma cholinesterase (ChE), and acetylcholinesterase activities reflected circadian rhythms. Hatching date affected total plasma ChE and butyrylcholinesterase (BuChE) activities, and levels of red-blood-cell hemoglobin (Hb) and hematocrit (HCT). In Choupal, HCT increased with brood size. Nestlings in Choupal had significantly lower protein and Hb levels, and higher glutathione peroxidase (GSH-Px) activity, during a drier year. Second-brood nestlings had significantly lower levels of Hb and HCT. Of the studied variables, only plasma BuChE and red-blood-cell GSH-Px activities were related to nestlings' survival to first winter and recruitment.

Song sharing among neighboring males is a well-known, frequent outcome of song learning in oscine passerines and some other groups, but only limited investigations of the spatial scale of this phenomenon have been pursued. On the basis of recordings of 1,043 individuals, we investigated song sharing in Dickcissels (Spiza americana) at local and regional scales at sites from northern Kansas to northern Oklahoma. Classification of song elements revealed decreasing song similarity with increasing distances between individual birds at small to intermediate scales, to ~10 km. At the largest spatial scales (10–300 km between sites), there was very little similarity among sites and no obvious tendency for a decrease in similarity with increasing distances among our 30 sites. At our intensively sampled site, analyses of quantitative measurements showed that, at least for our most widely shared song element, frequency and duration were more similar in closer birds. Thus, distance between birds influences both quantitative and qualitative song similarity in Dickcissels. Variability existed among sites in the shape of the song-sharing decay curve, which indicates that other factors besides distance also govern song-sharing patterns. We found high repeatability of individual songs for both second-year (SY) and after-second-year (ASY) males throughout the season, and high conformity to the local song neighborhood in both SY and ASY males from their first recording soon after arrival in May. Returning ASY males sang the same song they had produced the previous breeding season.

Many bird species migrate long distances without any food intake and must optimize storage of energy with respect to minimization of aerodynamic drag. To contribute to the understanding of this issue, we investigated, by magnetic resonance imaging (MRI), spatial distributions of body fat during the accumulation process before migration. We collected data from 12 Lesser Whitethroats (Sylvia curruca), 9 European Robins (Erithacus rubecula), 8 Blackcaps (Sylvia atricapilla), and 5 Willow Warblers (Phylloscopus trochilus). On average, each bird was examined 3.2 times. Adipose tissue was visualized using T1-weighted spin-echo MRI at 1.5 T. Fat-containing pixels were identified by an image-segmentation procedure. Data were analyzed with respect to (1) fat distribution within the body, (2) relationship between frontal surface area and fat mass increase, (3) fat mass increase in comparison with increase in total body mass, and (4) fat mass in relation to standardized visual classification of fat deposits. Fat increase was reflected by a larger frontal area, though adipose tissue was not deposited equally along the length of the bird. Slices with largest frontal area showed relatively low fractions of fat. Frontal area increased less than expected from conventional geometrical models, which indicates that the body shape is altered. The increase in total body mass was generally higher than the total fat mass increase, which indicates that other tissue, most likely flight muscle, can metabolize rapidly in correlation with fat accumulation. In Blackcap, total fat mass was not linearly related to standardized fat-deposit classes.