Understanding when species distributions should be ascribed to patterns in the physical habitat, rather than to the influence of social cues, is a crucial step in understanding avian habitat selection. To distinguish between these mechanisms, we assessed the point pattern of 213 Saltmarsh Sparrow (Ammodramus caudacutus) nests and the spatial autocorrelation of vegetation characteristics at two study sites. Our tests of aggregation at cumulative and discrete distance classes failed to detect any significant nonrandom pattern, which is consistent with the hypothesis that nest placement is random with respect to other nests. When the timing of nesting attempts was taken into account such that only previous or currently active nests were considered, there was still no evidence that females attempted to nest closer to other nests than expected given random site selection. The underlying spatial structure of the vegetation variables was somewhat patchy, but not in a way that was consistent between sites or that matched patterns in nest placement, which suggests that female Saltmarsh Sparrows do not distribute themselves within marshes according to these features. A lack of association between vegetation characteristics and the probability of nest flooding, which is the primary source of nest failure in this species, may explain the apparent lack of spatial structure.

We investigated the importance of passive sperm loss in the outcome of sperm competition in captive, wild-type Muscovy Ducks (Cairina moschata). In nature, Muscovy Ducks can be expected to experience more intense sperm competition than most other waterfowl because of their non-monogamous mating system. We estimated the instantaneous rate of sperm loss from the reproductive tracts of female Muscovy Ducks as 0.0235 ± 0.0018 h^-1 [SE], a fairly typical rate in comparison to the few other species of birds in which passive sperm loss has been measured. We also measured sperm precedence in trials in which a captive female was allowed to mate with two males in succession, with either a 24-h or a 72-h lag between matings. Paternity was determined with microsatellite markers. The mean proportion of a female's eggs fertilized by the second male (P₂) was 0.72 ± 0.14 in trials with the 24-h lag and 0.42 ± 0.13 in trials with the 72-h lag. The last-male precedence observed in the 24-h trials can be explained by a quantitative model in which passive sperm loss alone determines average success, but this model is not consistent with the outcome of the 72-h trials. Other factors, including perhaps postcopulatory female choice, must be acting in addition to passive sperm loss in the trials with the longer lag.

We used radiotelemetry to evaluate at-sea habitat use by Cassin's Auklets (Ptychoramphus aleuticus) that bred at Prince Island, off southern California, from 1999 through 2001. We used logistic regression to compare paired radiotelemetry (presence) with random (pseudo-absence) location-associated habitat variables derived from (1) satellite remote-sensing of sea surface temperature and chlorophyll-a concentration and (2) bathymetry. Compared with random locations within their foraging area and after controlling for distance to colony, odds ratios indicated that Cassin's Auklets with dependent young occurred in relatively shallower, warmer, and chlorophyll-rich water associated with chlorophyll fronts near the insular shelf break. These oceanographic features characterize habitats that support key euphausiid prey (e.g., Thysanoessa spinifera) and also other krill predators. Radiotelemetry combined with satellite remote-sensing of the ocean provides an alternative to vessel-based surveys for evaluating seabird foraging habitats. In the absence of information on the actual distribution, abundance, and, hence, availability of Zooplankton prey for seabirds, environmental factors can serve as proxies to help elucidate distributional patterns of seabirds at sea.

We used radiotelemetry to investigate the spatial behavior of wintering Bicknell's Thrushes (Catharus bicknelli) at a mid-elevation rainforest site and a high-elevation cloud-forest site in the Dominican Republic. We also analyzed blood stable carbon isotopes and fecal samples to compare thrush diets at these two floristically and climatically distinct sites. Birds consumed a primarily fruit-based diet at the mid-elevation site and a primarily arthropod-based diet at the high-elevation site. Despite these dietary differences, individuals at both sites defended and maintained exclusive, minimally overlapping core use areas and home ranges. The mean size of both core use areas and home ranges was similar between males and females and between adults and first-winter birds. Presence of nonterritorial or “floater” individuals was low at both sites (2.7% and 5.6%). Birds at the arthropod-dominated site were observed significantly more often on or within 1 m of the ground than birds at the fruit-heavy site, which were more often observed in the mid-canopy structure above 2 m. Birds at both sites displayed agonistic behaviors toward conspecifics and toward playback of conspecific vocalizations. Exclusive territoriality was the predominant winter social system, and we suggest that both arthropods and fruit are defensible resources for wintering Bicknell's Thrushes.

To understand the effects of foraging behavior on the amount of food provided to chicks (meal mass and frequency), we monitored nest attendance and diving behavior of 20 Adélie Penguin (Pygoscelis adeliae) pairs that were rearing chicks. Because ice forms on the sea surface at night, parents foraged through cracks or within leads in the sea ice mainly during 0800–2400 hours. Birds that departed the colony in the afternoon and returned in the evening of the same day fed their chicks more frequently than those that made longer trips (i.e., those that departed in the afternoon and returned the next day or departed in the early morning and returned that evening). When the duration of the longest dive bout during each trip was longer, parents brought back heavier meals that contained larger krill. On average, birds made longer dive bouts when diving to greater depths. Thus, daily foraging pattern and foraging depth affected the provisioning rate, but the proportion of time spent foraging during the potential foraging period, total underwater time per day, and parental body condition were not. We suggest that temporal variability in prey availability and individual differences in foraging behavior affect the provisioning rate and, thus, chick growth.

Frugivorous birds are expected to maximize pulp ingestion and, hence, prefer large fruits. Experience and learning may play a role in fruit-size choices, and species may also have innate preferences. We investigated preference for fruit size of Oneseed Hawthorn (Crataegus monogyna) in wild and naive Eurasian Blackbirds (Turdus merula). The preference patterns of wild and naive birds were similar, although greater differences were found among fruit-size classes in wild birds. When presented with a similar number of fruits per size class, both naive and wild birds preferred large fruits. However, when the same fruit mass per size class was offered, they reduced overall fruit consumption, and preferences for large fruits became weaker. The results suggest that Eurasian Blackbirds behave as energy-intake maximizers when feeding on Oneseed Hawthorn fruit and that they are driven, to some extent, by innate preferences for fruit size. However, birds in aviaries may not always behave in the same way as their wild counterparts, and further work is needed to verify that wild birds behave similarly under natural conditions.

The adrenocortical response to perturbation varies considerably within and across avian species during breeding. Among the factors hypothesized to influence this variation is the degree of parental care expressed by an individual. To increase our understanding of the relationship between parental care and the adrenocortical response, we examined corticosterone secretion in the polymorphic White-throated Sparrow (Zonotrichia albicollis) during three breeding stages: prelaying, incubation, and nestling. In addition, we reevaluated previously described morph differences in parental behavior. Tan-striped males provisioned nestlings at higher rates than white-striped males, which is consistent with earlier findings. However, in contrast to previous studies, provisioning rates were similar between female morphs and higher than those exhibited by either male morph. We found that, in males, the more parental morph (tan-striped) expressed a reduced adrenocortical response during the nestling stage, but the less parental morph (white-striped) did not. Females of both morphs exhibited similar and reduced adrenocortical responses during parental stages. In addition, we observed morph differences in baseline corticosterone during the nestling stage: less parental birds (white-striped males) had higher baseline corticosterone levels than more parental birds (females and tan-striped males). These findings support the hypothesis that modulation of baseline corticosterone and the adrenocortical response during breeding is a function of the degree of parental care expressed by an individual. By influencing how parents balance self-maintenance and parental care on a daily basis, or in the face of perturbation, baseline corticosterone and the adrenocortical response may play a role in the alternative reproductive strategies of White-throated Sparrow morphs.

The production of some types of signals is often assumed to be cost-free, yet we know relatively little about the factors that affect signal development. In birds, many plumage signals are produced by the pigment melanin being deposited into growing feathers. Birds synthesize melanin in a complex pathway involving many potentially limiting resources, one of which may be dietary calcium. We tested the effect of dietary calcium on the development of the black throat patch (bib) of juvenile male House Sparrows (Passer domesticus). Subjects were maintained throughout their molt on artificial diets containing either a low, medium, or high level of calcium, or a bicarbonate control diet with a low level of calcium but an acid—base balance equivalent to that of the high-calcium diet. Dietary calcium affected the size of the bib, but not in the predicted direction: birds on the low-calcium diet produced the largest bibs. Birds on the bicarbonate control diet produced bibs intermediate in size that were significantly smaller than those on the low-calcium diet, which suggests that acid—base balance may also influence melanin-based signals. Dietary calcium also had a broader physiological effect; birds on the low-calcium diet were in better condition than those on other diets, but only the calcium treatment explained significant variation in bib size. Although our treatments affected bib size, our results indicate that access to dietary calcium is not a general mechanism for condition dependence of melanin-based ornaments.

We studied growth in the Green-rumped Parrotlet (Forpus passerinus), a small Neotropical parrotlet that has an unusually long nestling period (28–35 days) and feeds nestlings nutritionally poor seeds. We asked why nestlings grow slowly even though nest predation is their main mortality factor. We examined nutrient accretion and the development of thermoregulation and computed an energy budget until fledging. We described three periods of growth: (1) days 1–13, when peak accretion for sodium, lipids, and energy occurred; (2) days 14–22, when nestlings became endothermic and accretion for proteins, calcium, and phosphorus peaked; and (3) days 23–30, when nestlings reached 90% of the asymptotic values of body components. The deposition rate of lipids (logistic constant K = 0.33) was higher than that of protein (K = 0.19), ash and calcium (K = 0.20), and, particularly, phosphorus (K = 0.14). In concordance with their slow growth, nestlings became endothermic only 10 days before fledging, considerably later than expected from asymptotic mass. Total metabolized energy during the nestling period was 1,133.3 kJ, of which 59.2% accounted for resting metabolic rate and 26.2% for activity. Growth efficiency, the proportion of total metabolized energy allocated to tissue deposition, was 14.5%, one of the lowest reported for altricial nestlings. We argue that nestling growth was not energy-limited and that limiting nutrients were deposited slowly as a result of restrictions imposed by low availability of protein and phosphorus in the diet. We propose that slow growth and poor diets are interrelated in Green-rumped Parrotlets and other Psittaciformes, but the direction of the causal relationship between them is unclear.

Spontaneous oscillator synchrony has been documented in a wide variety of electrical, mechanical, chemical, and biological systems, including the menstrual cycles of women and estrous cycles of Norway Rats (Rattus norvegicus). In temperate regions, many colonial birds breed seasonally in a time window set by photoperiod; some studies have suggested that heightened social stimulation in denser colonies can lead to a tightened annual reproductive pulse. It has been unknown, however, whether the analog of menstrual synchrony occurs in birds—that is, whether avian ovulation cycles can synchronize on a daily timescale within the annual breeding pulse. We report every-other-day clutch-initiation and egg-laying synchrony in a breeding colony of Glaucous-winged Gulls (Larus glaucescens) and show that the level of synchrony declined with decreasing colony density. We also pose a mathematical model based on the hypothesis that preovulatory luteinizing hormone surges synchronize through social stimulation. Model predictions are consistent with observations. Finally, we suggest a procedure for identifying synchronous egg laying in other colonies and species.

Roads may have detrimental effects on many bird species, but areas adjacent to roads also provide habitat and food for some species. To address the influence of roadside habitat on the federally threatened Florida Scrub-Jay (Aphelocoma coerulescens), we compared foraging effort, the amount of food collected, and estimated energy intake in three habitat types: (1) edges along a paved road (roadside), (2) edges created by human-maintained habitat without a road (pasture), and (3) natural scrub-dominated areas with minimal human-maintained edges (interior). We used focal watches of male breeders during three stages of the breeding season (incubation, nestling, and fledged young) in two consecutive years to assess variation in food availability and energetic intake among the three habitat types. Florida Scrub-Jays in roadside habitats handled (consumed, cached, or fed to their mate or offspring) significantly more food items and spent less time foraging during the nestling stage than interior and pasture jays, but no differences in handled food were found among the three habitat types during the incubation and fledgling stages. Although they spent less time foraging, roadside jays had higher rates of energy intake than interior and pasture jays during the incubation stage. There were no differences in these measures of foraging during the incubation, nestling, and fledgling stages between interior and pasture jays. Our results suggest that roads or roadside habitat, not simply edge habitats, have a positive effect on food availability and energy intake in Florida Scrub-Jays, although the patterns differ across breeding stages.

We show that the topology of separate elements in avian compound rhamphothecae are strongly similar among different clades, not only in external appearance but in how these elements conform to underlying structures. We conducted a morphological survey of 81 extant bird species and tested superficial similarities in external beak morphology for substantive similarity in associated skeletal structures and nerve courses. A revised set of morphological characters for compound rhamphothecae was optimized onto three recent phylogenetic trees to assess the relationships of homology and homoplasy in rhamphothecal morphology. Osteological correlates of rhamphothecae from the extinct basal ornithurine birds Hesperornis and Ichthyornis show that compound rhamphothecae are the primitive state for the clade including extant birds (Neornithes). Simple rhamphothecae are the result of the loss of softer keratinous grooves between rhamphothecal components, and there are many examples of transitional forms between compound and simple rhamphothecae in which the grooves remain as shallow depressions without a pronounced edge. Ancestral-character-state reconstructions of rhamphothecal morphology within Neornithes also show a considerable amount of homoplasy. We suggest that frequent homoplasy in rhamphothecal morphology is the result of underlying similarity in facial development.

Examination of contact zones between closely related species is important for understanding speciation, because the interactions in such zones may change the evolutionary direction of one or both taxa. To expose the composition and dynamics of a contact zone between two dove species, Streptopelia vinacea and S. capicola, we used mitochondrial DNA, amplified fragment-length polymorphism (AFLP) markers, and morphological and color measurements. We combined a field study on contact-zone and parental-species individuals with an examination of F₁ hybrids reared in captivity. We found that the contact zone is a narrow hybrid zone characterized by a high frequency of hybrids, a lack of clear parental species forms, a high incidence of S. capicola mtDNA, and an AFLP marker distribution more similar to that of S. vinacea. In morphology and color, field hybrids were more similar to S. vinacea and significantly different from S. capicola. F₁ hybrids were more similar to S. capicola in color. The laboratory data showed that both types of mixed matings produced viable F₁ offspring. Taken together, the results indicate the existence of a unimodal hybrid zone with asymmetric introgression from S. capicola into S. vinacea. The origin of this hybrid zone is most likely a combination of geographic and behavioral factors and suggests a balance between dispersal and selection.

We examined the population genetics and phylogenetics of Falcipennis canadensis isleibi, a subspecies of Spruce Grouse from the Alexander Archipelago of southeast Alaska, which was recently given subspecies status on the basis of subtle differences in plumage coloration and its limited distribution on several islands. The taxonomic status of Fc. isleibi is particularly consequential, both because little is known about its evolutionary, demographic, and conservation status and because island endemics often face high extinction risks. Samples were collected from central Alaska, British Columbia, and Prince of Wales (POW) and Zarembo (ZAM) islands in the Alexander Archipelago and identified to subspecies using established morphological traits. We sequenced the cytochrome-c oxidase I (COI) subunit of the mitochondrial genome (n = 62) and genotyped each individual at six nuclear microsatellite loci (n = 65). Individuals from POW and ZAM shared a unique mitochondrial haplotype not observed in other populations of other subspecies (F. c. franklinii and F. c. canadensis), whereas haplotypes were shared by individuals identified as franklinii or canadensis. Microsatellite loci revealed significant divergence among all subspecies populations ( = 0.352) as well as divergence between POW and ZAM populations of F. c. isleibi. These data corroborate the morphological classification of F.c. isleibi as a separate subspecies. Spruce Grouse are not managed as a single species by the state of Alaska, but instead as an aggregate with other forest grouse species. Our results indicate that populations of F.c. isleibi warrant special management attention to maintain this distinct evolutionary lineage.

Sexual size dimorphism occurs throughout the animal kingdom, and its ecological and evolutionary causes and implications have been intensively studied. Sex-specific differences in bill curvature are known in several species of birds, including some tropical hummingbirds. Despite the importance of bill shape for foraging, comparative studies of sexual dimorphism of bill shape are few. We quantified bill shape in two temperate hummingbird species, Black-chinned Hummingbird (Archilocus alexandri) and Ruby-throated Hummingbird (A. colubris) and compared patterns of sexual shape dimorphism. Several commonly used bill-curvature indices yielded contrasting results; one found differences between species and sexes, a second identified no differences in curvature, and a circle-curvature approach revealed shape differences between species and between the sexes. By contrast, landmark-based geometric morphometric methods identified significant differences in sexual shape dimorphism and also revealed that Ruby-throated Hummingbirds exhibited significant sexual differences in shape, whereas Black-chinned Hummingbirds did not. Female Ruby-throated Hummingbirds exhibited relatively greater bill curvature than males, a pattern consistent with observations of some tropical hummingbirds. Although the causes of differences in bill-shape dimorphism between Black-chinned and Ruby-throated hummingbirds remain unclear, we hypothesize that it may be attributable to differences in the structure of the community in which each species breeds and the interplay between inter- and intraspecific competition for resources in these communities. Finally, we recommend that future studies of bill shape include geometric morphometric approaches because they are better suited than univariate approaches for identifying more complex shape differences within and among species.

The riparian habitats of the arid southwestern United States provide critical stopover habitat for avian migrants, but they have been severely altered by invasive tamarisk (Tamarix spp.). The responses of birds to such habitat alterations are not well understood. We combined ecological and physiological measurements to provide an integrative assessment of how tamarisk invasion affects the stopover ecology of vernally migrating Wilson's Warblers (Wilsonia pusilla) along the San Pedro River in Arizona. Despite higher arthropod biomass in native cottonwood—willow habitat, the refueling rate of Wilson's Warblers, as measured by plasma metabolite profiling, was higher in tamarisk. Density and detections of Wilson's Warblers did not differ between habitats, but both measurements were significantly higher in cottonwood—willow habitat for the other members of the Wilson's Warbler foraging guild. Our measurements of food resources and migrant densities suggest that cottonwood—willow may provide high-quality stopover habitat. But when plasma metabolites are included, our results indicate that tamarisk offers superior habitat for refueling Wilson's Warblers, possibly because of release from high interspecific competition in cottonwood—willow. Our results demonstrate the importance of measuring refueling performance in the assessment of stopover habitat quality and the value of including plasma metabolite profiling in studies of avian stopover ecology.

Temporal and energetic constraints associated with migration may compromise plumage quality and, ultimately, flight ability in migratory birds. As a consequence, migrants may invest more resources in parts of the plumage that are essential for long, sustained flight (such as the primary wing feathers) than in less important feather tracts. We used migratory and sedentary Blackcaps (Sylvia atricapilla) to analyze within- and between-individual variation in the mass and quality of wing and tail feathers. Migratory Blackcaps in both adult and juvenile plumage had lighter tail feathers than sedentary Blackcaps, but the primary feathers were of similar mass. Interestingly, the quality of primary and tail feathers (estimated from the mass of the feather in relation to its size) were positively correlated within individuals. However, migratory individuals had higher-quality primary feathers than sedentary individuals, given the quality of their tail feathers. Therefore, migratory Blackcaps appeared to preferentially allocate limited resources to primary feathers at the expense of the quality of the less important tail feathers. We suggest that this represents an adaptive mechanism to reduce the costs of migration constraints on plumage functionality.

Helminthic parasites occur at high frequencies in waterbirds, but little is known about their effects on host population dynamics. In 2004–2005, we examined the effect of helminthic parasites on fledging success of semiprecocial American Coot (Fulica americana) chicks by experimentally dosing day-old chicks with the anthelmintic drug fenbendazole (treatments) or sterile water (controls) and measuring their survival to 40 days of age using mark—resighting analyses. In 2005, we also provided anthelmintic (treatment) or plain (control) supplemental food to incubating adults to determine whether chick survival was further influenced by parasite burdens of parents. Treated offspring had approximately half as many helminthic parasites as untreated offspring, but we could not demonstrate a reduction in parasite burdens among treated adults. Chicks that received fenbendazole in 2004 had 0.510 (85% confidence interval [CI]: 0.447–0.588) cumulative survival to 40 days of age, versus 0.387 (85% CI: 0.305–0.462) survival in untreated chicks. In 2005, offspring survival to 40 days posthatch was an additive function of both offspring and parental treatment, with survival averaging 0.578 (85% CI: 0.502–0.654) when both parents and chicks were treated, 0.461 (85% CI: 0.381–0.544) when only chicks were treated, 0.452 (85% CI: 0.375–0.533) when only adults were treated, and 0.334 (85% CI: 0.254–0.424) when neither was treated with fenbendazole. Our results provide compelling evidence that treatment with anthelmintic drugs increased fledging success and suggest that parasite burdens have important consequences for offspring survival in American Coots.

Life-history theory suggests that long-lived bird species will adjust their nesting effort according to current conditions to balance the costs and benefits of current reproduction with their long-term needs for survival and future reproduction. However, responses to the same habitat conditions may differ between species, even within the same ecosystem, to produce different nesting and population patterns. We examined differences in the nesting ecology of two sympatric wading species, Great Egret (Ardea alba) and White Ibis (Eudocimus albus), between years with high (2006) and below-average (2007) prey availability in the Florida Everglades. Clutch size of White Ibises decreased by ∼19% from 2006 to 2007, whereas Great Egret clutch size remained constant. Model selection identified rain, water depth, Julian date, year, and prey biomass as parameters that most influenced daily survival rates (DSR) of White Ibis nests, whereas nest stage, region, Julian date, water depth, and the quadratic form of water recession rate most influenced Great Egret nest DSR. Daily survival for both Great Egret and Whites Ibis nests was higher in 2006 (DSR = 0.992 and 0.999, respectively) than in 2007 (DSR = 0.981 and 0.979). Our results support the hypothesis that prey availability and hydrological factors play crucial roles in regulating populations of wading birds in the Florida Everglades. Results also demonstrated that White Ibis reproduction was more sensitive to changes in hydrological conditions and prey availability than Great Egret reproduction.

The rapid multiclutch mating system of the Mountain Plover (Charadrius montanus) provides an opportunity to examine sex differences in natal, within-year, and between-year breeding dispersal. We used nest locations over a 14-year period from a population of Mountain Plovers breeding on prairie dog colonies in Montana to examine sex-related patterns in natal and within-year breeding dispersal. Additionally, we modeled between-year dispersal distances in relation to sex, previous nest fate, and the occurrence of sylvatic plague in the colonies. We also modeled successive nest fate using dispersal distance and these same covariates. We found no evidence of sex differences in distances moved during natal dispersal (mean = 13.0 km for 16 males; mean = 10.2 km for 22 females) or within-year breeding dispersal (mean = 2.8 km for 22 males; mean = 3.0 km for 26 females). The mean (± SE) dispersal distance was 2.7 ± 0.60 km (n = 115) for males nesting in consecutive years and 4.3 ± 0.87 km (n = 87) for females. Previous nest fate was the only factor that had a strong effect on between-year breeding dispersal. On average, birds that were previously successful moved 3.0 ± 0.55 km (n = 149), whereas unsuccessful birds moved 4.6 ± 1.18 km (n = 53). None of the effects tested was suitable for predicting subsequent nest fate. Our work provides a better understanding of dispersal in an uncommon shorebird, additional insight into a novel mating system, and a basis for testing theories of avian dispersal.

We describe Laniarius willardi, a new species of boubou shrike (Malaconotidae) from the Albertine Rift of Africa. The most conspicuous, distinguishing morphological feature of the species is a gray to blue-gray iris. This and external morphometric data indicate that L. willardi is diagnosable from other black or sooty boubous. Further, L. willardi is genetically diagnosable, and its closest relative is the Mountain Sooty Boubou (L. poensis camerunensis) from Cameroon. The Crimson-breasted Bush-shrike (L. atrococcineus) and the Lowland Sooty Boubou (L. leucorhynchus) are together the sister clade to L. willardi—L.p. camerunensis. Laniarius willardi and the geographically codistributed L. p. holomelas differ by 11.5% in uncorrected sequence divergence, and elevational data taken from museum specimens suggest the possibility of elevational segregation of the species at ∼2,000 m, with L. willardi occurring at lower elevations. Our broad sampling of black and sooty boubou taxa indicate that (1) races of Mountain Sooty Boubou (L. poensis) do not form a monophyletic clade; (2) L. p. camerunensis may represent multiple, nonsister lineages; and (3) at least one race of Fülleborn's Black Boubou (L. fuelleborni usambaricus) is genetically distinct from other races of that species.

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.