Natal dispersal is a key life-history component that may be influenced by the fitness consequences of inbreeding. We studied natal dispersal and inbreeding within a large population of cooperatively breeding, endangered Red-cockaded Woodpeckers (Picoides borealis). We assessed the costs of close inbreeding, the spatial distribution of related males and its relationship to dispersal distance of females, and the change in dispersal behavior of females in the presence of closely related males. Close inbreeding resulted in a significant loss of fitness, through two separate effects: closely related pairs (kinship coefficient ≥ 0.125) exhibited lowered hatching rates and lowered survival and recruitment of fledglings relative to unrelated pairs. Despite a highly predictable spatial clustering of closely related males near the female's natal territory, natal dispersal distance of females was not sufficient to avoid these males as mates. Females changed dispersal behavior in the presence of closely related males on the natal territory: female fledglings were significantly more likely to disperse from natal territories if there were closely related males breeding there in the following year. Females did not change dispersal behavior in the presence of related males that were not on the natal territory. We suggest that dispersal behavior is a trade-off between benefits of short-distance dispersal, e.g., an advantage in competing for scarce breeding vacancies, and the substantial cost of close inbreeding.

Dispersal data are inevitably biased toward short-distance events, often highly so. We illustrate this problem using our long-term study of Acorn Woodpeckers (Melanerpes formicivorus) in central coastal California. Estimating the proportion of birds disappearing from the study area and correcting for detectability within the maximum observable distance are the first steps toward achieving a realistic estimate of dispersal distributions. Unfortunately, there is generally no objective way to determine the fates of birds not accounted for by these procedures, much less estimating the distances they may have moved. Estimated mean and root-mean-square dispersal distances range from 0.22–2.90 km for males and 0.53–9.57 km for females depending on what assumptions and corrections are made. Three field methods used to help correct for bias beyond the limits of normal study areas include surveying alternative study sites, expanding the study site (super study sites), and radio-tracking dispersers within a population. All of these methods have their limitations or can only be used in special cases. New technologies may help alleviate this problem in the near future. Until then, we urge caution in interpreting observed dispersal data from all but the most isolated of avian populations.

We studied recruitment and dispersal of White-tailed Ptarmigan (Lagopus leucurus) breeding in naturally fragmented alpine habitats at four study sites in Colorado from 1987–1998. Almost all recruitment for both sexes, particularly females, was of birds produced outside local populations and also external to nearby studied populations. Populations were more dependent on female recruitment than on male recruitment to sustain them, and patterns of recruitment were not correlated with local survival of adults or production of young the previous year, except at one site for females. Over 95% of recruits were yearlings. Breeding dispersal of adults, an infrequent but regular event, was also important to inter-population connectivity. Our data for multiple populations allowed us to describe movement patterns among populations to assess consistency with conditions required for a rescue system. After widespread reproductive failure in one year, we expected all populations the next year would have low recruitment due to a reduced supply of recruits produced in the region. Recruitment was low, but impact varied among populations. We conducted an over-winter study of radio-marked offspring to determine possible influences of winter site location and relatives on recruitment patterns. Contrary to expectation, offspring remained on or near breeding sites in winter, but were not located near their mothers or siblings. Recruitment location was related to winter site location. White-tailed Ptarmigan exhibit a well developed capacity for external recruitment that allows them to persist in small populations with stochastic conditions for breeding and survival. Extensive external recruitment may be a general pattern for birds.

Neotropical migrant birds have undergone significant changes in population size, due in part to alterations in the landscape in their breeding range. Some alterations have resulted in the isolation of areas containing optimal habitat for breeding. Isolation between habitat fragments could reduce gene flow between populations, which might result in loss of genetic variation due to genetic drift. To test whether isolation due to distance between populations may affect migratory birds as much as sedentary birds, we used four microsatellite loci as genetic markers to compare gene flow and population structure in migratory and sedentary House Wrens (Troglodytes aedon and T. musculus, respectively). If migratory behavior enhanced gene flow, we expected to find that populations of migratory birds were genetically more similar than populations of sedentary birds, and that gene flow declined more rapidly with distance in sedentary than in migratory populations. Blood samples were collected from 18–25 migratory House Wrens at each of six sites in Ohio separated by distances from 25 to over 300 km, and from 16–20 sedentary House Wrens at each of six sites in Costa Rica, also at distances up to 350 km. We used heterologous microsatellite primers to obtain estimates for R_ST (population subdivision) and Nm (number of immigrants per generation) in relation to distance between pairs of populations. In the migratory populations, Mantel permutational tests showed no effect of distance on R_ST or Nm at distances between 25 and 300 km. In the sedentary birds, R_ST increased and Nm decreased significantly as distance between populations increased from 25 to 300 km. F_ST values were not different from those obtained using Slatkin's (1995) R_ST statistics. These results are consistent with our hypothesis that migratory behavior enhances gene flow.

I documented the use by nesting birds and availability of arboreal termite nests (termitaria) in the Peruvian Amazon. Birds occupy about 1% of the termitaria annually, suggesting that termitarium availability does not limit reproductive output. Birds choose termitaria that are larger and higher than average, and the three most common termitarium-nesting species differ in their use of termitaria. Two species of Brotogeris parakeets use termitaria with similar characteristics, but Tui Parakeets (B. sanctithomae) nest in young forests and edge habitats whereas Cobalt-winged Parakeets (B. cyanoptera) use mature forests. Termitaria used by Black-tailed Trogons (Trogon melanurus) are larger and lower than those used by the two Brotogeris species. The contention that birds usually nest in termitaria still occupied by termites was upheld, but the presence or absence of termites did not explain a significant proportion of the difference between used and available termitaria after removing the effects of height, volume, and substrate type. Birds choose to nest in termitaria inhabited by both termites and aggressive biting ants (Dolichoderus sp.). These ants may be protecting the birds' nests by attacking predators or by providing a sort of “olfactory camouflage.”

I tape-recorded and counted the songs of color-banded Golden-cheeked Warblers (Dendroica chrysoparia) on Fort Hood, Texas in 1993 and 1994 to determine whether males use a two-category song system common to many wood-warbler species. More than 97% of all songs I documented belonged to two categories: A and B. A songs were higher in frequency, shorter, less complex, and were delivered at lower rates than B songs. Males used A songs primarily early in the nesting season, when near females, and from the interior of territories. In contrast, B songs were more common later in the nesting season, at dawn, and when males sang near territory boundaries. Songs delivered near territory edges were usually sung from one or two preferred perches on each male's territory that often coincided with the edge of a cliff or a break in the forest canopy. Based on these data, and in contrast to the implications of an early account of Golden-cheeked Warbler song use, this species shares the song system used by many wood-warbler species. Furthermore, the patterns of song use that I observed suggest that males do not sing randomly with respect to time or location on territory, and monitoring efforts that assume random singing across time and space may result in inaccurate or biased estimates of population sizes and habitat preferences.

We assessed the effect of beak morphology on the acoustic structure of woodcreeper (subfamily Dendrocolaptinae) songs using a comparative analysis of independent contrasts. For the song of each species, we measured the maximum and minimum frequencies, the bandwidth, and the emphasized frequency. Residuals of variation in beak length and acoustic frequencies after controlling for body size and phylogeny were calculated for each species and compared. We found a negative relationship between the residuals of acoustic frequencies and the residuals of beak length. This relationship was significant for emphasized frequency when we excluded two open-habitat species, Scimitar-billed Woodcreeper (Drymornis bridgesii) and Narrow-billed Woodcreeper (Lepidocolaptes angustirostris). This result is consistent with the hypothesis that the suprasyringeal vocal tract has resonating properties that affect the frequency spectrum of the song.

We determined the numerical and functional responses of migrant Bald Eagles (Haliaeetus leucocephalus) feeding on spawning kokanee salmon (Oncorhynchus nerka) at Hauser Reservoir, Montana from 1991–1995. Number of Bald Eagles was positively correlated with the fluctuating number of salmon carcasses during four of five years. Immigration and emigration rates were similar across years and were facilitated by several behavioral and physical characteristics of eagles: group foraging, communal roosting, and keen eyesight. Number of subadult eagles showed closer synchrony with density of salmon carcasses than did adult eagles. Eagles scavenging for salmon exhibited a Type II functional response. Handling times of scavenging eagles remained constant across the range of salmon carcass densities, whereas daily attack rates increased. Functional responses of scavenging eagles differed between age groups; adults exhibited a Type I response, whereas that of subadults could not be characterized. Handling times of scavenging adults were constant, but those of subadults increased with salmon density. Attack rates of scavenging adults increased with salmon carcass density. Consumption rates differed between age groups and among eagles using foraging modes of scavenging, stooping, and pirating, which suggests that eagles viewed live and dead salmon as alternative prey types. Bald Eagle scavenging of kokanee salmon was inversely density dependent.

We describe the diet of the Magnificent Frigatebird Fregata magnificens at Isla Isabel off the Pacific coast of Mexico based on 158 regurgitates (555 prey items) from males, females, chicks, and juveniles. The diet included 50 species of fishes (21 identified to genus only), 1 species of squid, and 2 species of crustaceans. Diplectum pacificum and Anchoa lucida were the most frequent species of fish in the frigatebird's diet. No differences in prey composition or prey size were found between males and females, but females disgorged 62% more food. This difference mirrors the bigger size (15% larger than males) and larger contribution of females to chick feeding. Flying juveniles consumed prey in different proportions than the adults and disgorged marginally more food. Juveniles may obtain food in different patches than adults and complement this source with maternal feedings, or they may be more likely to regurgitate. Diet composition of males, females, and flying juveniles changed during the 4-month period of this study, but the mass of regurgitates did not change as the breeding season progressed, suggesting that availability of prey species changes over time. Most of the diet of this population probably comes from opportunistic feeding on fisheries, because the variety of fishes disgorged is remarkably similar to the published list of fishes discarded by prawn-fishing boats in the area. If our assumption is true, kleptoparasitism and direct fishing are only marginally represented in the diet of this population.

We used a new immersion monitor to study the foraging movements of two species of albatrosses that nest in the Hawaiian Islands. The monitors showed that breeding male Black-footed Albatrosses (Phoebastria nigripes) land on the water more frequently during the day than at night. Breeding male Laysan Albatross (Phoebastria immutabilis) behavior was more variable and also showed a diurnal bias. We found no evidence of a nocturnal foraging bias in either species; in particular, these species do not seem to be limited to live capture of nocturnally available squid. Such squid may, nonetheless, contribute to the diet as a result of scavenging.

We analyzed patterns of species richness, size, structure, and composition of mixed-species flocks in relation to forest fragment size and forest successional stage during dry and rainy seasons, at the state of Minas Gerais, southeastern Brazil. Three forest fragments (1.7, 50, and 200 ha) were used for fragment size analysis, and two fragments (200 and 300 ha) were used for successional stage analysis. Fragment size and season affected flock richness, size, stability, and composition. In the 1.7-ha fragment, flock species richness, size, and stability were significantly different only during the rainy season. Fragment successional stage also influenced flock richness and size, although season did not. Flock composition also had changes related to fragment successional stage. Fragment geometry seems to be an important factor influencing flock structure and composition.

We tested whether Hooded Warblers (Wilsonia citrina) avoided abrupt forest edges by radiotracking males breeding in small, isolated forest patches (0.5–2.0 ha) in northwest Pennsylvania. Because territory edges were synonymous with abrupt forest edges in all cases, we compared space use patterns with males radiotracked in a nearby continuous forest (150 ha), where we defined edge from territorial boundaries. Based on the proportion of edge to core area, males in both habitats avoided the area within 20 m of the edge, implying that males responded to the presence of territory edge rather than forest edge. Surprisingly, however, males in isolated fragments used the edge area significantly more than males in continuous forest, even when measured against the relative amount of edge area within each territory. Elevated levels of edge use were not related to distance of nests to edges, nest stage, or time of day. We conclude that the presence of physical edges is not the sole determinant of territorial space use in this species and there are likely additional social factors influencing occupancy rates in small, isolated woodlots. Therefore, definitions of forest-interior species based on edge use need to be reconsidered.

We investigated population trends, adult survival, and productivity indices of a breeding population of Warbling Vireos (Vireo gilvus) in north coastal California using capture-recapture data from 19 years of standardized mist-netting conducted at Point Reyes National Seashore. We found significant long-term declines in abundance of both breeding and migratory Warbling Vireos. In addition, we found a significant long-term decline of hatching-year birds captured during the breeding season. The number of new adults in a given year, defined as those birds not previously banded and assumed to be an index of adult recruitment, was significantly correlated with the capture rate of hatching-year birds in the previous year, suggesting a link between reproductive success and adult abundance and recruitment. Our analysis of capture-recapture data provided an estimate of 50.4% for adult annual survival, similar to estimates for other species in stable populations. We could detect no temporal trend in survival. Nest survivorship from areas near our netting site was relatively low. We suggest that the decline of breeding and migratory populations of Warbling Vireos observed in coastal California may be the result of low productivity on the breeding grounds.

Using museum specimens, I document the molt cycles and molting grounds of the Gray Vireo (Vireo vicinior). During prebasic molts, adult female Gray Vireos replace their primaries in 57 days, whereas adult males take 70 days; all body plumage is replaced during this molt. Prebasic molts occur almost exclusively on the breeding grounds; just 3 of 41 specimens replacing primaries were collected away from breeding grounds. No molting specimens were collected from wintering areas. Prealternate molt occurs on the wintering grounds, and appears limited to the replacement of innermost secondaries and a limited molt of body plumage. By performing prebasic molt on breeding grounds, the Gray Vireo differs from several other western breeding passerine species that use desert regions of the southwestern United States and northwestern Mexico to exploit late summer food resources. The areas of these southwestern desert regions used by other species form a small portion of the breeding grounds, and encompass the entire wintering grounds, of Gray Vireos. I hypothesize that this contrast in molting regions is not due to differences in the general timing of prebasic molts among these species; rather, the contrast may be due to constraints imposed on Gray Vireos by a dietary shift to fruit during winter and the need to defend winter territories.

We studied nesting effort and success of Northern Pintails (Anas acuta) in southern Alberta. Annual nesting success estimates ranged from 6–18%. Clutch size averaged 7.2, and declined in a simple curvilinear fashion with nest initiation date. We found no relationship between egg size and clutch size or evidence from one year to the next of a trade-off between current and future investment in eggs. Within-year renesting rate ranged from 55%, based on a sample of 20 decoy-trapped females that lost their first nests to predators, to 85% based on a sample of 13 nest-trapped females forced to renest when we removed their clutches. Greater investment in initial clutches led to longer delays in laying replacement clutches. Because delays in renesting are costly (late-nesting females produce fewer offspring), females must contend with a trade-off between maximizing reproductive output in initial clutches versus the risk of delayed renesting if the first clutch should fail. We suggest that pintail reproductive traits have evolved primarily in response to short nesting seasons and variable environments.

We examined the influence of vegetation and predator community on nesting success of songbirds in the grasslands of eastern North Dakota, USA. Each year, eight sites were chosen: four were subject to predator removal, and four were non-removal sites. On each site, nests of grassland songbirds were monitored, and simulated nests were used to examine how vegetation characteristics at nests affect nest success. Vegetative characteristics at simulated nests did not differ from those at natural nests, but successful natural nests had greater forb and lesser grass cover than unsuccessful nests, whereas no differences in vegetation were detected between successful and depredated simulated nests. On non-removal sites, small mammals and ground squirrels (Spermophilus sp.) depredated nests in taller and denser cover when compared to nests destroyed by medium-sized mammals and birds. On removal sites, we found no difference in vegetation characteristics of nests depredated by different predator types. However, each group of mammalian predators depredated simulated nests with different vegetation characteristics on removal versus non-removal sites. On sites where predators were removed, small mammals and ground squirrels preyed on simulated nests in shorter vegetation containing fewer forbs, ground squirrels preyed on nests with higher grass cover and lower vertical density, and medium-sized carnivores preyed on nests in taller vegetation. These results support the hypothesis that high predator diversity may reduce the chance of “safe” nest sites, and suggest that the behavior of low-level predators may change when top-level predators are removed.

I used behavioral, meteorological, and laboratory metabolism data to calculate daily energy expenditure (DEE) in seasonally acclimatized Mountain Chickadees (Poecile gambeli) and Juniper Titmice (Baeolophus griseus). Analyses of laboratory metabolic data revealed that foraging energy requirements were not significantly higher than alert perching energy requirements. Respective DEE of chickadees and titmice were 48.8 kJ day⁻¹ and 48.3 kJ day⁻¹ in summer and 66.3 kJ day⁻¹ and 98.7 kJ day⁻¹ in winter. DEE as a multiple of basal metabolic rate (BMR) was 2.31 in summer chickadees and 1.91 in summer titmice. DEE was 2.70 times BMR in winter chickadees and 3.43 times BMR in winter titmice. The marked increase in calculated DEE in winter birds compared to summer is in contrast to a pattern of increased DEE in the breeding season for several avian species. These data suggest that winter may be a period of even greater stringency for small birds than previously believed.

We examined Bar-tailed Godwits (Limosa lapponica), a long-distance migratory shorebird, for evidence of dehydration toward the end of their 4,300-km migratory flight from West Africa to the Dutch Wadden Sea. Bar-tailed Godwits are ideal subjects for research on flight range constraints because they can readily be caught in migratory flight. Because godwits are capable of long nonstop travel, we hypothesized that they are physiologically adapted to minimize en route water loss, and therefore, do not experience water imbalance under standard migratory conditions. To test this hypothesis, we compared the hydration state of flying Bar-tailed Godwits at the end of a long bout of migratory flight to that of recently-landed godwits. Flying godwits were hydrated to the same degree as birds with free access to water, suggesting that godwits maintain water balance during migratory flight. To corroborate these empirical results, we ran a theoretical simulation of flight-incurred loss of water and energy in a male Bar-tailed Godwit based on the published model by Klaassen et al. (1999). When a low body drag is assumed, model output suggests that Bar-tailed Godwits flying at altitudes ranging from sea level to 3,000 m will avoid dehydration, and that flight at about 3,000 m will result in the longest possible flight range.

We estimated daily rates of nest predation and Brown-headed Cowbird (Molothrus ater) parasitism as well as nesting success for the Red-eyed Vireo (Vireo olivaceus), Blue-headed Vireo (V. solitarius alticola), Wood Thrush (Hylocichla mustelina), and Worm-eating Warbler (Helmitheros vermivorus) at two study sites in the middle Appalachian mountains from 1995–1998. These daily rates were then used in combination with species-specific life history parameters to estimate seasonal fecundity. Although daily predation rates were similar across species and sites, parasitism rates and nesting success differed within species between sites and among species within a site. The vireos generally experienced the highest rates of parasitism and subsequently the lowest estimates of seasonal fecundity. However, differences in parasitism and nesting success were not always an accurate predictor of seasonal fecundity. Despite significantly different estimates of nesting success, the Red-eyed Vireo and Blue-headed Vireo had similar estimates of seasonal fecundity. In contrast, estimates of nesting success for the Worm-eating Warbler and Wood Thrush were similar yet there were differences in seasonal fecundity. Life history attributes such as season length, ability to produce additional broods, and ability to raise a host young with a cowbird young were important in determining seasonal fecundity among species. We show the importance of including multiple species within a study framework and illustrate how predation and parasitism differentially affect these species with respect to seasonal fecundity.

We studied mixed-species insectivorous bird flocks in pine-oak forests in Middle America during three winter seasons to determine whether patterns of flock structure and dynamics were similar to those reported from other tropical sites. We also analyzed patterns of association among bird species, as well as their foraging behavior and the vegetation characteristics associated with birds in flocks. We encountered 333 flocks containing 144 species, of which 26 species had adequate sample sizes for analyses. The size and rate of movement of the flocks were similar to those reported from other Neotropical sites, however, the species richness of our flocks was lower than reported in most other studies, perhaps due to simpler vegetation structure or higher latitude. Only 3 of 50 significant correlations between species pairs were negative, indicating that species generally were not restricted in their participation in mixed-species flocks by other species. In only one instance did we observe correspondence between the association of species-pairs in flocks and their foraging behavior. For most species there was no relationship between association between species-pairs in flocks and vegetation parameters with which they were associated. Thus, additional factors besides foraging facilitation and mutual association with particular vegetation characteristics must be responsible for many of the positive correlations among species pairs. We suggest that non-random association among species within flocks may result in part from enhanced vigilance for predator detection afforded by flock members using similar parts of the environment at the same time.

We tested the responses of two bird species which nest on unmovable substrates (e.g., cavities and walls) to simulated and actual egg damage in their nest. Tree Swallows (Tachycineta bicolor) and Barn Swallows (Hirundo rustica) removed broken eggs and continued to incubate the rest of their clutch, but response times took up to 8 days, and observed rejection rates were lower than reported for some other passerines. Collectively, these data and other studies suggest that broken eggs represent a continuing selection pressure to which all birds respond, although there appears to be some variability among species in the strength and speed of the response to damaged eggs.

We tested the hypothesis that bill proportions at hatching are a byproduct of overall skull proportions which are a result of constraints of brain growth. We measured brain and eye weights, eye diameter, and some skull dimensions in domestic geese (Anser anser f. domestica) varying in age between embryonic day 7.5 and 29.5 (hatching), and in five adult geese. With respect to age, weights show divergent growth patterns resulting in complex allometry for eye but simple allometry for brain weight. This differs from the situation in Galliforms and probably reflects the high cerebralization of Anseriforms. Length measurements show similar growth patterns. Cranial length realizes a larger part of overall growth during incubation when compared to facial length. Cranial width is similar to eye diameter and brain weight. Bill width exhibits a unique growth pattern. Bill proportions are similar to the whole head but differ from those of the bony brain capsule. Therefore, although all craniometric measurements strongly correlate to brain size, brain growth probably influences growth of the cranial but not of the facial part of the skull.

We examined the communities of bacteria and fungi associated with the cloaca of adult House Sparrows (Passer domesticus) to investigate whether microbes could be transferred during copulation and thus represent a cost to mating. The levels of microbes in the cloacae of the male and female of eight breeding pairs were significantly correlated. The levels of microbes on the rim of the cloacal protuberance, which comes into direct contact with another bird during copulation, were similar to those inside the cloaca. These findings are consistent with microbes being transferred during copulation. Females could also receive non-cloacal pathogens during copulation, given that two of five males sacrificed had microbes within their testes, which could be incorporated into the ejaculate. Undeveloped eggs were screened for the presence of microbes, although only a low proportion (18%) was contaminated. It seems unlikely that microbial contamination is a general cause of egg failure in this species.

House Sparrow (Passer domesticus) nestlings were screened for ectoparasites; the most common ectoparasite was Pellonyssus reedi, a haematophagous mite. Parasite load was used to determine whether: ectoparasites have an effect on chick body mass prior to fledging, relative chick body mass is a within-brood predictor of relative parasite load, and parasite load per brood correlates with brood size. There was a negative correlation between parasite load and chick body mass, indicating that ectoparasites can reduce the quality of host offspring. Within broods, a chick's body mass was not related to its parasite load relative to its siblings' loads, suggesting that these ectoparasites do not preferentially target particular nestlings based on size. No relationship was found between brood size and total parasite load; thus, there was no evidence that within-nests, mite population size is limited by brood size.

We measured antibodies to infectious bursal disease virus (IBDV) in blood of nesting Common Eider (Somateria mollissima) females and immature Herring Gulls (Larus argentatus) in the Baltic Sea, and in blood of Spectacled Eider (Somateria fischeri) females nesting in a remote area of western Alaska. Positive (≥ 1:16) IBDV titers occurred in 75% of the eiders and 45% of the Herring Gull chicks. In eiders, the prevalence of positive titers differed among locations. We found no evidence that IBDV exposure impaired the immune function of Herring Gull chicks, based on their response to inoculation of sheep red blood cells. We suggest that eider ducks and Herring Gulls have been exposed to IBDV, even in locations where contact with poultry is unlikely. The presence of this virus in wild bird populations is of concern because it causes mortality of up to 30% in susceptible poultry.

We tested whether contamination of avian blood by the parasite Haemoproteus could cause the amplification of false positive genetic markers generated by random amplified polymorphic DNA (RAPD). DNA was extracted from blood taken from five Rock Doves (Columba livia) infected with Haemoproteus, and one uninfected control individual. A drug treatment was administered to clear the infection, and a second DNA sample extracted. The parasitized and unparasitized DNA samples were used in RAPD reactions with 20 different 10-nucleotide primers, which produced 178 well-resolved markers. In no case were any of the reaction products specific to the parasitized samples, and in almost all cases the products were found consistently across all replications of infected and non-infected samples. The high ratio of avian to parasite DNA and the greater genome complexity of the host probably prevents the amplification of markers unique to parasite species such as Haemoproteus.

Transmitters were attached to four adult male Cory's Shearwaters (Calonectris diomedea) caught at their breeding sites off Crete, Greece, in autumn 1998. The birds had left the Mediterranean by the beginning of December. Two were last recorded in the eastern tropical Atlantic in January/February. The other two wintered east of the Mid-Atlantic Ridge, one at about 10°N, the other one in equatorial waters, and could be tracked until return migration in March/April. The seasonal variation in travel speed is in accordance with a conventional pattern of migration with phases of migration and wintering, rather than continuous movement throughout the nonbreeding cycle. The birds left the Mediterranean later and wintered farther north than expected. We suggest that the known longitudinal cline in body size, morphology, and vocalizations of Cory's Shearwater may also be found in migration behavior.

Age classes of migrant songbirds often differ in migration timing. This difference creates the potential for age-ratios recorded at stopover sites to vary with the amount and distribution of sampling effort used. To test for these biases, we sub-sampled migrant capture data from the Middle Rio Grande Valley of New Mexico. We created data sets that reflected the age ratios of migrants that would have been captured with stratified and concentrated designs at four levels of mist-netting effort. Analysis of these data indicate that age-ratios of Neotropical migrants varied significantly with sampling design, but not with sampling effort. More after-hatch-year Neotropical migrants were captured with stratified than with concentrated sampling designs. Age-ratio of temperate migrants did not vary with either amount of sampling effort or sampling design. Sampling design is an important consideration in the interpretation of age ratios among stopover sites, and standardization of sampling among sites could improve our understanding of differential migration of age classes.

We studied the time-activity budgets of Harlequin Ducks (Histrionicus histrionicus) molting at the Gannet Islands, Labrador in the summer of 1998. For the entire population, a large proportion of time was spent hauled out of the water (61.4%), and resting (53.5%). Only a small proportion of time was spent foraging (11.6%). Male Harlequin Ducks undergoing the pre-basic molt were hauled out of the water significantly more (92.2%) than males in basic plumage (8.1%). Males undergoing the pre-basic body feather molt foraged significantly less (1.7%) than males in basic plumage (17.7%). Harlequin Ducks do not appear to increase their food intake to meet the nutritional requirements of molt. Instead they may try to reduce thermoregulatory and maintenance costs by engaging in activities that do not consume much energy, and by staying out of cold water while their plumage is not intact. Furthermore, they may deliberately lose body mass while molting to regain the ability to fly at an earlier stage of wing molt.

Rufous Bush Chats (Cercotrichas galactotes) show a conspicuous tail color pattern consisting of terminal white and subterminal black patches which are shown in tail display during nest defense, aggression, and courtship. Multiple linear regression of visual tail features of males showed that in the two years of study, birds with higher bilateral symmetry in the black patches attained higher seasonal reproductive success, mated earlier in the season, and their nests were less likely to be depredated. In one year, birds with greater white terminal patches also attained higher reproductive success and their nests were less likely to be depredated, and in the other year birds with longer tails paired earlier. I suggest that these tail features have an effect on reproductive success by facilitating early pairing and/or by diminishing nest predation.

We use 13 color characters to describe the first known Dendroica nigrescens × D. occidentalis hybrid. Because this specimen was collected in the southeastern Cascade Mountains of Washington during the breeding season, D. townsendi, D. occidentalis, and D. nigrescens are the only plausible parents for a hybrid male falling within the black-throated clade of Dendroica warblers. Multiple character states in the hybrid refute the alternative parental combinations, townsendi × occidentalis and townsendi × nigrescens. Two characteristics of this hybrid suggested further tests of the parentage of 38 problematic hybrids that were treated previously as townsendi × occidentalis recombinants by assumption only. These hybrids lack yellow on their breast, the only character that refutes a nigrescens × occidentalis parentage. The new hybrid is intermediate between nigrescens and occidentalis in the color of its posterior face and its anterior crown; thus, we scored these new characters in the 38 problematic hybrids. None of these 38 specimens was intermediate or white in either of these regions, and there was no correlation between having tinges of white in these regions and the extent of flank streaking. These results fail to support nigrescens in the parentage of these 38 specimens; furthermore, none of the problematic hybrids carried a nigrescens mitochondrial DNA haplotype. Thus, we conclude that all are unusual recombinants of townsendi × occidentalis hybridization, rather than nigrescens × occidentalis hybrids.