This study uses mitochondrial DNA (mtDNA) to examine the phylogeography of the White-headed Woodpecker (Picoides albolarvatus), one of the least-studied woodpeckers in North America. A mismatch distribution and calculation of Tajima's D indicate that the overall phylogeographic history of the species is characterized by a recent range expansion that probably occurred after the start of the Pleistocene. In addition, a nested clade phylogeographic analysis indicates that additional processes such as allopatric fragmentation and restricted gene flow have influenced the evolutionary history of this species. Traditionally, the White-headed Woodpecker has been split into two subspecies whose distributions meet in the northern part of the Transverse Ranges in California. The two subspecies differ morphologically, with the southern subspecies having a larger bill in proportion to its body size than the northern subspecies. Geographical variation in mtDNA is concordant with a division at the Transverse Ranges that corresponds to the morphological variation seen between the two subspecies. An analysis of molecular variance indicates that 27% of the genetic variation results from differences between the northern and southern subspecies. Furthermore, birds in the northern part of the range differ from those in the southern part of the range by at least one base substitution. These results agree with the hypothesis that the larger bill of the southern subspecies is the result of recent local adaptation to feeding on the large cones of Coulter pines (Pinus coulteri).

Given the difficulty of following free-living, dispersing juvenile songbirds, relatively little is known about when, where, how, and from whom these young birds learn their songs. To explore these issues, we studied the Chipping Sparrow (Spizella passerina), males of which have a single, simple song, but populations of which may contain 20–30 different songs. In our western Massachusetts study sites, we color-banded 324 nestling and 32 fledgling sparrows. Twelve of these banded males returned to our study areas, dispersing a few hundred meters to 1.8 km away from their natal territories. The song of each yearling closely matched only one of his immediate neighbors on the breeding territory, revealing that a yearling sparrow precisely imitates one of his close neighbors after dispersal. Evidence from this field study and a previous laboratory study show that a young male is able to learn songs either during his hatching year or the following spring, perhaps depending on his chances of song exposure or social interaction with territorial neighbors.

Previous research on individual differences in the acoustic structure of vocalizations and vocal recognition has largely focused on the contexts of parent-offspring interactions, territory defense, sexual interactions, and group cohesion. In contrast, few studies have examined individual differences in the acoustic structure of mobbing and alarm calls. The purpose of this study was to explore individual differences in the acoustic structure of the inflected alarm caw of the American Crow (Corvus brachyrhynchos). The alarm caws of 15 wild, marked individuals were recorded and 25 acoustic measurements were made automatically using customized software. A stepwise discriminant function analysis showed that 20 of the 25 variables were important in discriminating among individuals, with 65% classification success. We used factor analysis to reduce the large number of variables to a set of seven meaningful call features. All of these features differed among individuals, suggesting that American Crows have the potential to discriminate among individual birds on the basis of call structure alone. Five of the features differed between the sexes, with call frequency being the most significant. One clearly subordinate male clustered with the females, raising the possibility that social status partially determines the sex-based differences. Encoding of individual identity in alarm contexts may be adaptive if receiver vigilance and approach urgency depend on the status, reliability, or family membership of the alarm signaler.

Life-history theory predicts that longer-lived, less fecund species should take fewer risks when exposed to predation than shorter-lived, more fecund species. We tested this prediction for seven species of dabbling ducks (Anas) by measuring the approach behavior (behavior of ducks when approaching potential landing sites) of 1099 duck flocks during 37 hunting trials and 491 flocks during 13 trials conducted immediately after the 1999–2000 waterfowl hunting season in California, USA. We also experimentally manipulated the attractiveness of the study site by using two decoy treatments: (1) traditional, stationary decoys only, and (2) traditional decoys in conjunction with a mechanical spinning-wing decoy. Approach behavior of ducks was strongly correlated with their life history. Minimum approach distance was negatively correlated with reproductive output during each decoy treatment and trial type. Similarly, the proportion of flocks taking risk (approaching landing sites to within 45 m) was positively correlated with reproductive output. We found similar patterns of approach behavior in relation to other life-history parameters (i.e., adult female body mass and annual adult female survival rate). Thus, species characterized by a slower life-history strategy (e.g., Northern Pintail [A. acuta]) were more risk-averse than species with a faster life-history strategy (e.g., Cinnamon Teal [A. cyanoptera]). Furthermore, although we were able to reduce risk-averseness using the spinning-wing decoy, we were unable to override the influence of life history on risk-taking behavior. Alternative explanations did not account for the observed correlation between approach behavior and life-history parameters. These results suggest that life history influences the risk-taking behavior of dabbling ducks and provide an explanation for the differential vulnerability of waterfowl to harvest.

We documented the local density and sex, age-class, and body size distributions of Western Sandpipers (Calidris mauri) among habitats at Bahía Santa María, northwestern Mexico, during the nonbreeding season. Three habitats were recognized: brackish flats, mangroves, and cattail marshes, which we ranked as richest to poorest in food resources and safest to most dangerous in predation danger. Western Sandpiper population structure differed among habitats. Bird densities were highest in brackish flats, the richest and safest habitat, and males and adults of both sexes were overrepresented. In cattail marshes, which appeared to be the poorest and most dangerous habitat, bird densities were lower, and the sex ratio and age ratios within each sex were more even. In mangroves, bird densities were similar to those in cattail marshes, but sex and age ratios were similar to those in brackish flats. Exposed culmen, an index of structural size, was not related to habitat use in either sex. Body mass of immature males was more variable than that of adults among habitats and immature males gained mass throughout the winter. Birds in brackish flats and mangroves were initially heavier, but tended to lose mass, whereas birds in cattail marshes were initially lighter, but tended to gain mass. Mass distributions thus converged in late winter. While the social and ecological causes and significance of differential sex and age-class distributions among habitats remain largely unquantified, evidence from this and previous studies suggests that nonbreeding population structure is a common phenomenon with important implications for migratory shorebirds.

We studied wintering Willow Flycatchers (Empidonax traillii) in two seasonal freshwater wetland habitats in northwestern Costa Rica during five boreal winters, to determine habitat occupancy, overwinter and between-year site and territory fidelity, and the degree to which the sexes maintain and defend winter territories. Both males and females used agonistic displays, song, and other vocalizations to maintain and defend mutually exclusive winter territories. Males were generally more abundant than females, but this varied by site and year. There was no significant difference in male and female territory size, nor any indication of sexual habitat segregation. Similarity in morphology and aggressiveness between the sexes may account for the lack of habitat segregation and the ability of females to maintain territories at wintering sites. Each year, 80%–92% of banded flycatchers that were present in midwinter remained at the site until late winter; of these, 86%–100% of individuals maintained the same territories throughout the entire period. We also observed nonterritorial floaters that subsequently established and held winter territories. Between-year site fidelity averaged 68%, and almost all returning birds established territories with boundaries similar to the previous year. Between-year apparent survivorship estimates ranged annually from 54%–72%, with no difference between sites but weak support for higher survivorship of males compared to females. Values for winter site and territory fidelity were generally higher than those reported for other species and for Willow Flycatchers on the breeding grounds; between-year survivorship estimates were similar to those reported for breeding flycatchers.

Although polygyny can potentially increase male reproductive success, the benefits of this strategy could be offset by losses to extra-pair paternity or reduced offspring survival. We developed microsatellite markers to assess the influence of extra-pair offspring (EPO) on reproductive success and paternity in monogamous and polygynous pairs of the facultatively polygynous Southwestern Willow Flycatcher (Empidonax traillii extimus). Based on genotypes of 140 offspring from 56 clutches over six years, 14% of nestlings in our study population were extra-pair offspring, with 23% of all successful nests containing at least one EPO. We found that polygynous males produced 2.11 ± 0.35 offspring per season, compared to 1.15 ± 0.18 for monogamous males. This increased reproductive success was due primarily to the increased number of nests of polygynous males, as the number of offspring per pair did not differ between monogamous and polygynous males. Twenty of the 140 genotyped nestlings were extra-pair offspring. Sires could be assigned to 16 of these; one polygynous male sired two EPO in one nest, two monogamous males sired eight EPO in two nests, and four nonterritorial males sired six EPO in four nests. Overall, these results indicate that in this population, females of polygynous males did not raise a disproportionate number of EPO as a result of the polygynous mating strategy of their mate, and that both territorial and nonterritorial males sired EPO.

Blue-black Grassquits (Volatinia jacarina) are small, granivorous, Neotropical birds that are abundant in central Brazil. During the reproductive season, the socially monogamous males acquire a blue-black plumage and defend very small, clustered territories that resemble leks. They execute a conspicuous courtship display that consists of a leap, revealing white under-wing patches, synchronized with a vocalization. We collected data on the morphology and behavior of banded males and characteristics of their territories to determine how these factors may influence acquisition of mates and nesting. For a second group of birds in the area, we used microsatellite genotyping to test the breeding synchrony hypothesis, which predicts that tropical species that breed synchronously should exhibit high rates of extra-pair fertilization (EPF). We found that males that successfully formed a pair bond differed from unsuccessful males in their behavior, but not in morphological attributes or territory features. Successful males spent more time in their territories, executed displays for longer periods and at greater rates, and their display leaps were higher. These results point to the greater importance of behavior relative to other factors in the successful reproduction of Blue-black Grassquit males. In the second group of birds, EPFs occurred in 63% of 11 nests and involved 50% of the 20 chicks sampled. This exceptionally high incidence of EPF in the small sample analyzed occurred in diverse contexts, including intraspecific parasitism and quasi-parasitism, a rare type of maternity loss where the resident female is parasitized by other females that were fertilized by the resident male. A short and highly synchronized breeding season, clustered breeding in small territories, and granivorous habits may contribute to the high rates of EPF in this tropical species.

Few studies have examined how avian life-history traits vary within populations as elevation increases and climate becomes more severe. We compared egg and clutch sizes of Mountain Bluebirds (Sialia currucoides) nesting at two elevations (1500 m and 2500 m above sea level) in the Bighorn Mountains of Wyoming over two years. Eggs laid by females at the high-elevation site were, on average, significantly (6%) smaller in volume than eggs laid by their lower-elevation counterparts. Across elevations, egg size showed a significant positive correlation with female body condition (weight relative to size), and high-elevation females had significantly lower indices of condition than low-elevation females. Temperatures during clutch formation were colder at the high-elevation site, and egg size was negatively related to temperature after controlling for the effects of female condition. Clutches of females at high elevations were, on average, marginally smaller (by 5%, 0.3 eggs) than clutches of low-elevation females. Unlike egg size, clutch size was unrelated to either female condition or temperature during clutch formation. This suggests that, when under energetic or nutritional stress at high elevations, females sacrifice egg size before sacrificing clutch size.

Nestlings can exhibit considerable variation in developmental patterns both within and among locations due to differences in environmental conditions and parental investment. I investigated trade-offs between nestling growth rate and residual body mass (body condition) at three locations across the range of the Tree Swallow (Tachycineta bicolor). Nestlings at the northern extreme of the range in Alaska had slower growth rates, lower body mass, and higher residual body mass than nestlings in New York and Tennessee. High insect availability was correlated with increased growth rates of nestlings in New York and Tennessee, but not in Alaska. Conversely, nestlings in Alaska showed increased residual body mass with high insect availability, but nestlings in New York and Tennessee did not. The trade-off between growth rate and residual body mass varied among sites, with fast-growing nestlings in Tennessee maintaining a higher residual body mass than those in Alaska. These results suggest that factors affecting offspring growth and condition vary among sites, leading to geographical differences in offspring development trajectories.

In two contrasting breeding seasons, we investigated the effects of provisioning on chick growth and survival of the Magnificent Frigatebird (Fregata magnificens), a socially monogamous, dimorphic seabird that rears a single chick for more than a year, shows specialized feeding techniques, and depends on unpredictable food sources. We hypothesized that chicks of this seabird would increase their chances of survival by varying their growth in relation to food availability. We estimated the amount of food ingested by a chick using electronic scales placed at the nest and recorded feeding rates, growth rate, fledging size, and fledging age. Body mass and bill and ulna lengths were also measured. Not surprisingly, provisioning and growth were higher in the year with apparently higher food availability; however, developmental variables did not show the same pattern. This work shows a clear relationship between provisioning and growth and that growth variability occurs in this species. Understanding the relationship between provisioning and growth provides insight into life histories and elucidates the influence of variation in provisioning on fitness.

National parks in Alaska are generally assumed to be high-quality, undisturbed wildlife habitats. However, these parks attract recreational users, whose presence may reduce the suitability of key habitats for nesting shorebirds. In Kenai Fjords National Park, Black Oystercatchers (Haematopus bachmani) often breed on gravel beaches that are also popular campsites. In this study, we examined the effects of recreational activities in coastal Alaska on reproductive performance of Black Oystercatchers. We monitored survival of nests and chicks on 35 to 39 breeding territories annually during four breeding seasons (2001–2004). Most recreational disturbance on these territories occurred after the peak hatching date of first clutches. Annual productivity was low (average of 0.35 chicks per pair), but was not strongly affected by recreational disturbance. Daily survival of nests varied annually and declined over the season. Our results suggest that nest survival was lower during periods of extreme high tides. Daily survival rate of broods increased over the season and was higher on island than mainland territories, likely due to differences in predator communities. Territory occupancy rate and site fidelity were high; 95% of color-banded oystercatchers returned to the same breeding territory in the subsequent year. We conclude that Black Oystercatchers are resilient to low levels of recreational disturbance. However, in light of projected increases in recreation, we suggest managers move campsites away from the traditional nest sites identified in this study to minimize future disturbances.

Fire alters the structure and composition of shrublands and affects habitat quality for the associated avifauna. Because shrubland ecosystems have been greatly reduced from their original extent in western North America and fire is increasingly being used to manage these landscapes, a better understanding of how fire affects the associated vegetation and wildlife is imperative. We evaluated the response of Green-tailed Towhees (Pipilo chlorurus) to prescribed fire in the montane shrublands of Rocky Mountain National Park, Colorado during 2002 and 2003. Three to five years following prescribed burning, Green-tailed Towhee density and shrub cover were generally higher in unburned areas. Nests (n  =  179) were located in unburned vegetation; within burned sites, all nests were in remnant patches. Green-tailed Towhee nest survival was 57% (95% CI  =  49%–65%) across the two years of the study. More than half of the nests were in common juniper (Juniperus communis) shrubs, and nest survival was higher for nests in junipers than those in other shrub species. Daily nest survival rates were lower at the site with the highest density of towhees and declined over the breeding season. With regard to shrub cover, opposite trends were observed for nest-site selection and nest survival: nest plots had greater shrub cover than non-nest plots, but nest survival decreased with increasing shrub cover. Because shrub cover affects towhee density and nest survival in conflicting ways, fire management at Rocky Mountain National Park alters both habitat availability and suitability for Green-tailed Towhees.

We describe the timing and location of the prebasic molt in the Ash-throated Flycatcher (Myiarchus cinerascens), a hawking insectivore with resident populations in Mexico and migrant populations that breed in the western United States. The timing of fall molt with respect to migration is of particular interest for Ash-throated Flycatchers from the United States because they breed in arid lowland habitats that are probably unproductive in late summer, and because time constraints on molt might force northern populations to leave their breeding grounds before molting. Adults and juveniles depart their breeding grounds to arrive and molt in the region of the Mexican monsoon shortly after the monsoon rains begin. Diminishing food on the breeding grounds and increasing food in the monsoon region seem more important than time constraints for explaining molt-related movements by northern populations, because more southerly breeding birds east and west of the monsoon region also move to the monsoon region to molt. We found age class differences in the timing and duration of molt. In adults the primary molt starts approximately 14 July and requires 76 days to complete, whereas in juveniles, primary molt starts approximately 1 August (18 days after adults) but requires only 50 days to complete. We found no evidence that juveniles molt more primaries simultaneously than adults, so we conclude that the daily growth rate of individual feathers must be higher in juveniles than adults.

Arctic-nesting geese depend on nutrients acquired during spring migration for reproduction, and thus should attempt to maximize nutrient intake while on staging areas. We investigated site use of Black Brant (Branta bernicla nigricans) at an important staging location—Humboldt Bay, California—to determine whether birds selected the most profitable feeding areas available. Migrating Brant feed almost exclusively on eelgrass (Zostera marina), which is restricted in availability due to daily and seasonal tidal cycles. We mapped foraging Brant locations during low tides and collected eelgrass samples to describe food resources in 31 areas in the bay. We used negative binomial regression to evaluate goose densities during different tidal levels and times of season as a function of food biomass and nutrient content, distance from grit sites, and substrate elevation. Results varied by time of season and tidal depth, but Brant densities were positively correlated with eelgrass protein, calcium, and biomass in most analyses. Brant usually fed in the deepest possible areas permitted by tides, and closer to tidal channels, where biomass and nutrient content of eelgrass were greater and where depletion from grazing was probably less. During higher low tides, Brant fed closer to previously visited grit sites. Tide cycles change over the course of the Brant's staging period on the bay, enabling longer and more frequent access to deeper eelgrass meadows as spring progresses. These seasonal changes in tidal pattern coincide with seasonal changes in Brant use of the bay. Thus, migration patterns for estuarine bird species might be shaped by latitudinal gradients in both food phenology and seasonal tidal patterns.

Endogenous stores of energy allow birds to survive periods of severe weather and food shortage during winter. We documented changes in lipid, protein, moisture, and ash in body tissues of adult female Pacific Black Brant (Branta bernicla nigricans) and modeled the energetic costs of wintering. Birds were collected at the extremes of their winter range, in Alaska and Baja California, Mexico. Body lipids decreased over winter for birds in Alaska but increased for those in Baja California. Conversely, body protein increased over winter for Brant in Alaska and remained stable for birds in Baja California. Lipid stores likely fuel migration for Brant wintering in Baja California and ensure winter survival for those in Alaska. Increases in body protein may support earlier reproduction for Brant in Alaska. Predicted energy demands were similar between sites during late winter but avenues of expenditure were different. Birds in Baja California spent more energy on lipid synthesis while those in Alaska incurred higher thermoregulatory costs. Estimated daily intake rates of eelgrass were similar between sites in early winter; however, feeding time was more constrained in Alaska because of high tides and short photoperiods. Despite differences in energetic costs and foraging time, Brant wintering at both sites appeared to be in good condition. We suggest that wintering in Alaska may be more advantageous than long-distance migration if winter survival is similar between sites and constraints on foraging time do not impair body condition.

We combined Breeding Bird Survey point count protocol and distance sampling to survey spring migrant and breeding birds in Vicksburg National Military Park on 33 days between March and June of 2003 and 2004. For 26 of 106 detected species, we used program DISTANCE to estimate detection probabilities and densities from 660 3-min point counts in which detections were recorded within four distance annuli. For most species, estimates of detection probability, and thereby density estimates, were improved through incorporation of the proportion of forest cover at point count locations as a covariate. Our results suggest Breeding Bird Surveys would benefit from the use of distance sampling and a quantitative characterization of habitat at point count locations. During spring migration, we estimated that the most common migrant species accounted for a population of 5000–9000 birds in Vicksburg National Military Park (636 ha). Species with average populations of >300 individuals during migration were: Blue-gray Gnatcatcher (Polioptila caerulea), Cedar Waxwing (Bombycilla cedrorum), White-eyed Vireo (Vireo griseus), Indigo Bunting (Passerina cyanea), and Ruby-crowned Kinglet (Regulus calendula). Of 56 species that bred in Vicksburg National Military Park, we estimated that the most common 18 species accounted for >8150 individuals. The six most abundant breeding species, Blue-gray Gnatcatcher, White-eyed Vireo, Summer Tanager (Piranga rubra), Northern Cardinal (Cardinalis cardinalis), Carolina Wren (Thryothorus ludovicianus), and Brown-headed Cowbird (Molothrus ater), accounted for >5800 individuals.

Declines in avian populations highlight a need for rigorous, broad-scale monitoring programs to document trends in avian populations that occur in low densities across expansive landscapes. Accounting for the spatial variation and variation in detection probability inherent to monitoring programs is thought to be effort-intensive and time-consuming. We determined the feasibility of the analytical method developed by Royle and Nichols (2003), which uses presence-absence (detection-nondetection) field data, to estimate abundance of Mountain Plovers (Charadrius montanus) per sampling unit in agricultural fields, grassland, and prairie dog habitat in eastern Colorado. Field methods were easy to implement and results suggest that the analytical method provides valuable insight into population patterning among habitats. Mountain Plover abundance was highest in prairie dog habitat, slightly lower in agricultural fields, and substantially lower in grassland. These results provided valuable insight to focus future research into Mountain Plover ecology and conservation.

We investigated nest-hole excavation by the Red-naped Sapsucker (Syphrapicus nuchalis) in aspen (Populus tremuloides) woodlands in western Colorado. Sapsuckers excavate nest cavities primarily in aspens infected with a heartwood rot fungus (Phellinus tremulae), which softens the heartwood of infected trees. We assessed the interior condition of fungus-infected aspen trunks by extracting wood samples with an increment corer to determine whether sapsuckers chose nest-hole locations based on the extent of healthy sapwood remaining. Comparing fungus-infected trees with and without cavities, cavity-bearing trees had thinner healthy sapwood. The depth of healthy sapwood also varied with compass direction, being thinnest on the south sides of fungus-infected aspens. Cavity entrance orientations were significantly biased to the south-southeast, corresponding with the directional bias in heartwood rot. These results suggest that the depth of healthy sapwood, and hence excavation effort, may be important in determining nest hole location for the Red-naped Sapsucker.

Over four years, nestling Pied Flycatchers (Ficedula hypoleuca) were banded and recaptured in nest boxes at a 44 km long and 1–1.5 km wide study area along the Courish Spit on the southeast Baltic coast. The return rate for males was nearly twice as high as for females. Males settled significantly closer to their natal sites than predicted by the null model, which assumed that any nest box in the study area was selected at random. For females, the frequency distribution of natal dispersal distances was not significantly different from that predicted by the null model. The difference in average dispersal distance between the sexes was highly significant. Although some individuals settled within tens of kilometers, most male Pied Flycatchers settled within several kilometers of their natal sites. We suggest that even if females settle on average farther from their natal sites than males do, both sexes imprint on a relatively small (several kilometers in diameter) area during postfledging exploration, to which they return each spring.

We report the wing bones of a small passeriform bird from the early Oligocene of France, which are among the earliest fossil remains of Passeriformes in Europe. The specimen is clearly distinguished from oscines, to which all extant European passeriforms belong, and closely resembles suboscine passerines in presumably derived features. If future, more complete specimens support its assignment to the suboscines, it would be the earliest fossil record of this passeriform taxon. Together with other fossils from the early Oligocene of Germany, it indicates that nonoscine passerines colonized Europe before the arrival of oscines.

We report two new late Pleistocene avifaunas from New Mexico, recovered from Sandia Cave during archaeological excavations by F. Hibben in the 1930s and the nearby Marmot Cave excavated in 2000. The fossil assemblage from Sandia Cave consists of at least 30 taxa, including seven extralimital and two extinct species, Coragyps occidentalis (extinct vulture) and Ectopistes migratorius (Passenger Pigeon). The avifauna from Marmot Cave is limited to eight taxa shared with Sandia Cave. Two new records of Gymnogyps californianus (California Condor) are reported from these sites, as well as new records of Lagopus sp. (ptarmigan), Aegolius funereus (Boreal Owl), and Micrathene whitneyi (Elf Owl) from New Mexico. Two new radiocarbon dates on fossil G. californianus from Sandia and Marmot cave are reported at 10 795 ± 50 and 25 090 ± 220 ¹⁴C years before present (B.P.), respectively. These collections provide further evidence for mixed avian communities in New Mexico during the late Pleistocene and are similar to other cave avifaunas of comparable age from the Great Basin and Rocky Mountain regions. The birds from Sandia Cave that are shared with other fossil avifaunas include species currently found in arctic tundra, boreal, and steppe habitats, as well as open, xeric communities. This collection provides additional evidence for widespread steppe-tundra, shrub, and subalpine forest environments at lower elevations of western North America during the late Pleistocene.

We studied the breeding success of resident Bald Eagles (Haliaeetus leucocephalus) over a 20-year period along the Pit River drainage in northern California. In 258 nesting attempts at 10 intensively studied nesting territories, 0.31 to 1.65 young were produced per year per occupied territory (mean  =  0.97), with average nesting success of 62%. Nineteen individually banded breeding adult Bald Eagles produced from zero to 36 young during their lifetimes, and birds remained on their territories for 1–16 years following capture as adults. We calculated a 90% annual survival rate for breeding adults from our sample of 19 birds, with longevity of one banded eagle at 22 years. Eagles that bred on a territory for a greater number of years did not produce a greater number of young annually on average than other breeding birds. Larger males, as evidenced by body mass at capture, produced significantly more young over their lifetimes than smaller males. This same relationship did not hold for females, however. Seven banded pairs of adults remained together on their territories for 3–15 years. Reproduction decreased significantly following replacement of a breeding adult on a territory, and this effect continued for 2–3 years following replacement.

On 11 July 1985, an albino juvenile Great Frigatebird (Fregata minor) was collected by RWS and EAS on Christmas Island (2°N, 157°W) in the tropical Pacific. First observed on 13 July 1984 as a 55–60-day-old chick, the albino was seen flying about the colony on 4 November 1984 and again in February 1985. In July 1985 the juvenile was at its nest with such badly abraded plumage that it could not fly. Burtt (1986) proposed an aerodynamic model that predicts the distribution of melanic feathers in response to abrasion from airborne particles in a flying bird. The albino frigatebird provides a test of this model, since frigatebirds spend most of their time flying and rarely contact water, ground, or objects. Abrasion of the primaries and tail of this albino Great Frigatebird follows the pattern predicted by Burtt (1986). Furthermore, the pattern of damage to secondaries and tertiaries suggests that friction of feathers against each other is another important source of wear.

The relationship between the Brown-headed Cowbird (Molothrus ater) and its cavity-nesting hosts has received little attention because of the assumption that cowbirds rarely parasitize these hosts. We tested the Eastern Bluebird (Sialia sialis), a host that is sometimes heavily parasitized by cowbirds, for egg ejection behavior. Bluebirds ejected 65% of experimentally added cowbird eggs (n  =  20), but ejected no experimentally added conspecific eggs (n  =  66). This suggests that cowbird parasitism, not conspecific brood parasitism, is the selective pressure responsible for egg ejection in this species. This level of rejection may be conservative because bluebirds nest in dark cavities, which may make cowbird eggs difficult to detect by bluebirds.