At regular intervals throughout 2001, a unit from the Phelps Ornithological Collection assisted a biological survey along the Río Caroni in Venezuela, north and downstream of the Embalse de Guri. One of the expeditions was to Isla Carrizal at 07°54'N, 63°04'W, a large uninhabited island thickly covered with groves of spiney Guadua latifolia and Ripidocladus sp. bamboos, mixed with semideciduous forest and patches of savanna. On two occasions, three specimens of an unknown blue seedeater (Amaurospiza) were collected. Those were the first records for an Amaurospiza for northern South America, and subsequent investigation showed it to be a hitherto undescribed species.

Several European studies have indicated advances in breeding dates of birds in the last 30 years, which authors attributed to climate change. In North America, Dunn and Winkler (1999) reported a continent-wide advance of five to nine days in breeding dates of Tree Swallows (Tachycineta bicolor) between 1959 and 1991. I present results of an intensive study of Tree Swallows breeding on and near Long Point, Ontario, at four sites monitored 1969–2001, 1977–1986, 1978–2001, and 1987–2001. Local air temperatures varied among sites, according to distance from Lake Erie, but there was no significant regional trend in April and May temperatures between 1969 and 2000. Median and 10th percentile dates of clutch initiation by females that were at least two years old varied among years by up to 20 days overall and 18 days within sites, and differed by 0–14 days between sites in the same year. There were no significant differences in average timing of laying among the 1970–1980, 1980–1990, and 1990–2000 periods. Nevertheless, there was a significant trend towards earlier laying in 1990–2000, which was attributable to exceptionally early laying and warm May weather in 1998–2001. Across all sites, median dates of clutch initiation were strongly correlated with average daily maximum temperatures in the first four, five-day periods in May, but clutches at one site were initiated three days earlier than predicted by temperatures alone. I estimate that climate warming of 5°C in May could result in an average advance of about seven days in the median date of laying of Tree Swallows at those sites. My results indicate that spring temperatures are strongly correlated with timing of laying, but show that spring temperatures have not increased in the Long Point region and timing of the breeding season has not advanced throughout North America.

Poor breeding success often increases dispersal, but there is conflicting evidence about the putative adaptive benefits of dispersal behavior. Thus, observational and experimental data were analyzed to test whether breeding success (number of young fledging) influenced breeding and natal dispersal by Tree Swallows (Tachycineta bicolor), using information from 1,302 nests over 12 years. Success was experimentally altered at 291 randomly selected nest boxes by adding or removing three eggs (representing ±50% of modal clutch size). Finally, we tested whether dispersal distance, controlling for antecedent breeding success, had consequences for subsequent breeding success.

Contrary to predictions, (1) adult and natal dispersal distances were not significantly influenced by breeding success, and (2) manipulating success had no effect on either breeding or natal dispersal. Moreover, after controlling for antecedent breeding success, dispersal distance had no influence on subsequent breeding success. In most years of our study, >85% of nest initiations produced at least one fledgling, and individual boxes did not consistently have low or high fledgling production. Hence, swallows may have little to gain by dispersing out of our nest-box grid, and box-specific success did not provide a reliable cue about where to disperse within the grid. Thus, remaining in the grid for subsequent breeding attempts, regardless of fledgling production, could be interpreted as adaptive. Nonetheless, most adults remained close to the nest they had used in previous years, which suggests that some unmeasured influence, such as social interactions among neighbors, led to nonrandom dispersal.

We investigated movements and habitat use during breeding and postbreeding periods in Scarlet Tanagers (Piranga olivacea) during June-September 1998 in northern Virginia deciduous forest. Nine birds (8 males and 1 female) remained on the same home range during both breeding and postbreeding periods, whereas 11 birds (9 males and 2 females) shifted home range (>300 m) between periods. Breeding season home-range size ranged from 2.6 to 5.6 ha (95% kernel), and core area from 0.61 to 0.93 ha (50% kernel). Postbreeding home ranges were similar in size to home range during the breeding period for birds that remained in the vicinity of nesting areas, but were larger for birds that moved away from the nesting area. Scarlet Tanagers occurred in both mature and successional forest during breeding and postbreeding periods, with some indication of increased use of earlier successional stages during the postbreeding period. Needs for Scarlet Tanagers during the postbreeding period (molt, premigratory fattening) differ from those during the breeding period (pair formation, nest placement, rearing of young). Those differences provide a plausible explanation that all tanagers changed focal areas between breeding and postbreeding periods. These findings confirm the need for taking the postbreeding period into account, both for understanding migrant life history and successful conservation.

There is growing awareness that costs associated with egg production play a significant role in shaping avian life histories. The life-history strategy of the Thick-billed Murre (Uria lomvia), a colonial, cliff-breeding seabird of Arctic waters, is characterized by a high annual adult survival rate, deferred breeding, and laying of a single-egg clutch. The single-egg clutch is a widespread phenomenon among seabirds and is generally thought to reflect demands of chick provisioning, rather than egg production. We compared composition of eggs laid by Thick-billed Murres most likely to be physiologically constrained in their capacity to produce eggs (young females with no prior experience, and females forming replacement eggs) to that of first eggs laid by early laying females (typically older, more experienced members of the population). Young, inexperienced females laid 4–18 days past the populationwide median laying date, and their eggs averaged 13% lighter in mass than those laid by early layers. Compared to early laid eggs, shell mass on young females’ eggs was similar to that predicted from egg mass, but their eggs had a lower yolk-to-albumen ratio. There was little difference between the two groups in relative protein content of albumen, relative protein or lipid content of yolk, or amino acid makeup of protein in yolk or albumen. Replacement eggs averaged 6% lighter in mass than first eggs laid by the same females earlier that season. As with young females’ eggs, replacement eggs had shells similar in mass to that predicted from egg mass, but lower yolk-to-albumen ratios, when compared to early laid eggs. Both protein and lipid concentrations in yolk were similar in first and replacement eggs, but replacements were deficient in albumen protein. Amino acid makeup of protein in yolk and albumen was similar in the two groups. Those results suggest that any limitations on egg production acting on young, inexperienced females are manifested in delayed laying and reductions in overall egg mass and proportional yolk content, but not in variation in biochemical composition of their eggs. Limitations on females forming replacement eggs are manifested not only in reduced egg mass and yolk content (as with young females), but also in changes in the biochemical composition of eggs; in particular, evidence suggests that relaying females may face a deficit of endogenous protein. The existence of such limitations suggests that demands of egg production can be significant even in a species that lays a single-egg clutch.

According to the hypothesis that has been invoked most frequently to explain seasonal fattening patterns for birds—the “adaptive winter-fattening hypothesis”—individuals respond to worsening foraging conditions by increasing body mass and energy reserves. Two hypotheses have been proposed equally frequently to explain daily weight gain patterns for birds: according to the “state-dependent foraging hypothesis,” energy reserves should be amassed early during the day, when starvation risk increases; according to the “mass-dependent predation-risk hypothesis,” mass gain should be delayed for as long as possible, to minimize predation risk. Those hypotheses have been tested previously, using statistical methods (e.g. multiple-regression analysis) that assume independence among environmental variables (e.g. photoperiod and temperature). We conducted path analyses that included four predictor variables (day-in-season, hour-in-day, mean daily temperature, and daily precipitation) to model body-mass fluctuations for two small, nonhoarding (noncaching) passerine species that inhabit central eastern Sweden. Data were partitioned hierarchically into species, age class, gender, and season subgroups. As reported in many small passerine species studies, body mass increased during the day and maximized at dusk; over seasons, body mass increased during autumn, maximized by midwinter, and declined toward breeding in spring. Path analysis models accounted for 9.5–49.9% (mean 26.3%) for Blue Tit (Parus caeruleus) body mass variance and 1.8–52.3% (mean 16.8%) for Great Tit (P. major) body mass variance; for both species, accountability was lowest for autumn (Blue Tit,12.2%; Great Tit, 7.3%), highest for winter (Blue Tit, 33.4%; Great Tit, 21.9%), and intermediate for spring (Blue Tit, 22.7%; Great Tit, 11.8%); for Blue Tits, it was greater for adults than for juveniles (33.2 and 21.7%); whereas negligible for Great Tits (15.9 and 17.3%) and slightly greater for males than for females (Blue Tit, 27.4 and 23.5%; Great Tit, 23.1 and 21.3%). Those results are consistent with predictions formulated on the basis of the adaptive winter-fattening, partially with state-dependent foraging, and, possibly, mass-dependent predation-risk hypothesies and reveal that body-mass fluctuations are associated to a greater extent with photoperiod than with temperature.

We compared trends in the number of Hawaiian Petrels (Pterodroma sandwichensis; formerly Dark-rumped Petrels [P. phaeopygia sandwichensis]) and Newell's Shearwaters (Puffinus auricularis newelli) seen visiting Kauai, Hawaii, on ornithological radar in June 1993 and 1999–2001 and summarized and evaluated trends in the number of young Newell's Shearwaters recovered in the “Save Our Shearwaters” (SOS) Program on Kauai, 1979–2001. After pairing sampling dates at each site to remove temporal effects, radar data indicated that the number of Newell's Shearwaters visiting Kauai declined significantly between 1993 and 1999–2001. The mean change from 1993 numbers of radar targets across 13 sites was −59.8 ± 7.2% (SE) in 1999, −62.1 ± 5.5% in 2000, and −61.5 ± 5.4% in 2001, with all sites except one showing decreases of 38–93% in 1999 and all sites showing decreases of 31–96% in 2000 and 37–92% in 2001. Our data suggest that the decline is concentrated in Newell's Shearwaters, whereas the Hawaiian Petrel population actually appears to have increased. The SOS fallout data exhibited a consistent 72% overall decline in Newell's Shearwater recoveries from 1993 to 2001. Although we believe that the SOS data only generally reflect population size and productivity of shear-waters on Kauai, we conclude from the radar data that there has been a significant decrease in the number of Newell's Shearwaters visiting Kauai since 1993.

We compared habitat use and niche overlap in the closely related seabirds Kittlitz’s (Brachyramphus brevirostris) and Marbled (B. marmoratus) Murrelets in nearshore waters of Prince William Sound, Alaska, in 1996–1998, and examined the relationship between near shore habitat use and morphology of those two species. Within bays, the distribution of Kittlitz’s Murrelet groups diverged the most from randomness for the variables habitat type (preferring [i.e. using significantly more than what is available] glacial-affected and glacial-stream-affected habitats), distance to shore (preferring areas 51–100 m from shore), and water clarity (preferring highly turbid water), whereas the distribution of Marbled Murrelet groups diverged the most from randomness for the variables habitat type (preferring glacial-unaffected habitats), ice cover (preferring areas of no ice), and sea-surface temperature (SST) (preferring temperatures = 6°C). The probability of a group of birds being Kittlitz’s Murrelets was determined most strongly by water clarity. Kittlitz’s Murrelet groups were more common in the more heavily glaciated College and Harriman fjords than in the other two bays and more common in early and midsummer than in late summer; the reverse was true for Marbled Murrelet groups. Marbled Murrelet groups had the least niche overlap with Kittlitz’s Murrelet groups in water clarity, SST, and site, whereas Kittlitz’s Murrelets had the least overlap with Marbled Murrelets in habitat type and water clarity. Similarly, Kittlitz’s Murrelet groups occurred in water significantly more turbid than did Marbled Murrelet groups in two of four habitat types. Kittlitz’s Murrelets had eyes (as indicated by orbit diameter) that were significantly larger in proportional size than Marbled Murrelets. We propose that these two species are specialized for foraging in different water types, with specialization of the Kittlitz’s Murrelet for turbid water of glacial origin leading to optical specialization.

The Rufous Vanga (Schetba rufa) is a cooperative breeder. Although young males typically remain in natal territories, yearling females do not remain, but disperse to breed for themselves. The male-biased sex ratio likely restricts independent reproduction by young males. We analyzed demographic data from a seven-year study of the Rufous Vanga in Madagascar to estimate the mortality for each sex. We also examined the sex ratio at fledging and at hatching, sexing nestlings with DNA analysis on sex chromosomes. Analyses indicated that the biased sex ratio was due to differential mortality of fledglings rather than the bias at birth. We suggest that the delayed dispersal improved survival of auxiliary males.

Environmental quality has the potential to influence dispersal if cost of dispersing is outweighed by cost of staying. In that scenario, individuals experiencing different conditions in their natal area are expected to differ in their dispersal. Even if there is wide agreement that reasons behind the dispersal decision are multiple, it is often less clear what conditions actually add to the observed dispersal behavior. The scale at which the dispersal behavior is analyzed can also be of crucial importance for a correct understanding of the dispersal process. Furthermore, in long-lived species factors influencing dispersal behavior of juveniles may differ from those adding to dispersal of adults. Using 12 years of banding data (1989–2000), we studied dispersal behavior of Northern Goshawks (Accipiter gentilis) hatched over a wide area in Finland in relation to local demographic and ecological conditions. Hatching rank and hatching date added to the probability of leaving in the first place; whereas hatching date, local prey availability, and sex of the disperser were related to dispersal distance. Among adult birds ( 3 years), none of the analyzed variables were related to distance; whereas the probability of remaining locally was related to local grouse density in the hatching year (for males only). Results show that the combined effects of factors working at several levels act together on dispersal behavior in Northern Goshawks and highlight the importance of studying different age classes separately in long-lived species. In summary, our results suggest that goshawk individuals distribute themselves spatially in parallel with factors determining the costs and advantages of dispersing where philopatry seems to be connected to factors positively associated with survival; but to test the validity of that idea, more data on fitness consequences of dispersal are needed.

Cooperative breeding, in which more than two individuals live in a group and raise offspring, usually in a single nest, is found in only 3% of avian species. On the basis of a review of the literature, we found reports of groups (usually trios) at nest sites in 42 species of diurnal raptors. At least one example of cooperative breeding was found in 29% of genera and 14% of species, distributed in both Accipitridae and Falconidae. Given the difficulty of obtaining behavioral observations necessary to detect cooperative breeding in most raptor species, combined with the large number of species that have been poorly studied, cooperative breeding in diurnal raptors may be more common than our data indicate. However, when data on the sex of the extra bird(s) or relationships among group members were available, patterns were quite varied. For 7 of 13 species, groups primarily contained multiple adult males, though three of those species also had groups formed from offspring that had delayed dispersal; three species had a low, but regular, occurrence of multiple females (females of groups laid eggs in the same nest); and the remaining three species were characterized by having extra birds that were yearlings or subadults. In over half of species, groups did not appear to be composed of related individuals, contrary to many cooperatively breeding passerine species where groups are primarily composed of offspring that have delayed dispersal. Our review suggests that the evolution of group living in many raptors may be independent of delayed dispersal, and that the factors important in explaining the evolution of that behavior depend upon the benefits of group living.

Rates of infestation by the scaley leg mite (Knemidokoptes jamaicensis) were examined on two overwintering Nearctic-Neotropical migrants, Palm Warbler (Dendroica palmarum) and Prairie Warbler (D. discolor), in low-elevation desert thorn scrub and high-elevation pine forest in the Dominican Republic. Ectoparasites were common on birds in the dry thorn scrub where birds roosted communally, but were never found on birds in the moister pine forest where communal roosting was not detected. Prevalence of ectoparasites varied between years and generally increased in prevalence within winters, with mean rates of infestation reaching as high as 25% among Palm Warblers in late-winter. Parasitized Palm Warblers showed significant decreases in mean pectoral muscle mass scores indicating a negative effect on body condition and physiological stress. Infestation had a significant effect on overwinter site persistence and annual return rates; no infected individuals ever returned the following year. Results of a path analysis indicated that mite infestation was more important than general physiological condition (as represented by pectoral muscle score) in determining annual return. Data suggest that environmental variables and host behavior may affect parasite infestation rates, and further attention should be given to the potential contribution of parasite infestation to winter limitation of avian populations.

We conducted phylogeographic analyses of Motacilla flava (Yellow Wagtail) and M. citreola (Citrine Wagtail). We analyzed mitochondrial DNA sequences from 167 M. flava specimens obtained from 17 localities throughout Eurasia and Alaska, and 38 specimens of M. citreola obtained from 7 Eurasian localities. Phylogenetic analysis revealed three clades within traditionally recognized M. flava: Europe and southwestern Asia, northeastern Eurasia, and southeastern Asia. Those groups should be considered species, because together they are not monophyletic, and are interspersed with M. citreola, M. cinerea, and M. alba. Motacilla citreola also is paraphyletic, consisting of two species-level groups. Northeastern and southeastern groups of M. flava each appear to be sister taxa to eastern and western groups of M. citreola, respectively. Together those four groups form a clade, whereas the western M. flava group is considerably more distant. Within each of the three groups of M. flava, and the two groups of M. citreola, little phylogeographic structure was detected. Signatures of past population expansion are evident for some populations of M. flava; expansion is more recent in Moscow, Kursk (western group), Yamal, and Anabar (northeastern group), and older in Tyva and Vyatka (western group). A history of population stability is inferred for the Yamal population of M. citreola. Nested-clade analyses detected contiguous range expansion for southeastern M. flava and restricted gene flow with isolation by distance for northeastern M. flava and eastern M. citreola.

From May through July, 1993–1998 and 2001, effects of Brown-headed Cowbird (Molothrus ater) parasitism on 36 Warbling Vireo (Vireo gilvus) nests were documented in southwest Colorado. Overall parasitism was 75.0% and was the major source of nest failure. Among vireo nests that were not depredated, a significantly lower proportion of parasitized nests (10.2%) than nonparasitized nests (85.7%) fledged host young. Significantly fewer vireos hatched and fledged per nest and per egg in parasitized nests compared with nonparasitized nests. We observed no significant differences in mortality rates during the incubation stage between parasitized and nonparasitized nests. However, during the nestling stage, mortality rate was significantly higher in parasitized nests (0.17 nests lost per observation day) than nonparasitized nests (0.01 nests lost per observation day). Cowbirds almost always hatched 3 to 5 days before vireo nestlings. In two cases, vireo nestlings fledged from parasitized nests; in one nest the cowbird egg failed to hatch, and in the other nest the vireo hatched simultaneously with the cowbird. The low vireo production at that study site suggests that that area may be a sink population for Warbling Vireos.

Eyespots (color patterns resembling eyes) are present in many taxa and often have important ecological functions. In some taxa, potential functions of eyespots have not been extensively examined, as is the case with pygmy-owls (Glaucidium spp.), many of which bear a conspicuous eye-like pattern on their nape. Using wooden replicas of Northern Pygmy-Owls (G. gnoma), with and without eyespots, we tested one potential function: whether eyespots affect mobbing behaviors of small forest birds. We measured the orientation of mobbing behaviors (where birds perched and flew at the model) and intensity of mobbing bouts (duration of bouts and number of mobbing individuals). Eyespots affected the most proximal behavior, close passing (flights directly at the model, resulting in an approach within 0.5 m). When eyespots were present, mobbers shifted away from eyespots, providing the first empirical evidence for a link between eyespots and avian mobbing.

A removal experiment was conducted to measure how much and by what mechanisms brood parasitic Brown-headed Cowbirds (Molothrus ater) cause nest failures in a commonly used host, the Song Sparrow (Melospiza melodia). When numbers of female cowbirds were reduced experimentally, nest failures fell from 65.0% (n = 663 nests) to 49.9% (n = 331). Cowbird reduction reduced the frequency of nest failure to one-third of control levels in Song Sparrows during the last 80 days of the sparrow's breeding season, the period when most parasitic laying took place. Cowbird reduction decreased nest failures strongly at the egg stage, and weakly at the nestling stage. Daily nest-failure rates were independent of whether or not a nest was parasitized by cowbirds. Two hypotheses were tested to explain how cowbirds cause host nests to fail: first, egg removal by female cowbirds lowers clutch size below a threshold where the host deserts; second, cowbirds cause host nests to fail by destroying entire clutches or broods. In support of the first hypothesis, desertion following parasitism and egg removal was less frequent when cowbird numbers were reduced (8.9% of n = 158 nests) than for unmanipulated controls (16.5% of n = 424 nests). In support of the second hypothesis, there were fewer cases where young were killed in the nest, or found dead near it, after cowbird numbers were reduced (2.5% of 158 nests) than in controls (4.7% of 424 control nests). In contrast, proportions of nests that failed after the disappearance of all eggs, young, or both, and after unparasitized clutches were deserted, increased when cowbird numbers were reduced. Although our study supports both hypotheses, cowbird-induced desertion had a greater effect on nest failure rates than did cowbird predation. Our study suggests that cowbird removal programs are likely to benefit commonly used and endangered hosts by reducing rates of nest failure.

Effects of bacteria on avian hosts in the wild have received little attention until recently. Whereas the pathogenic effects of bacteria are well known, positive effects of symbiotic bacteria are more rarely considered. Nestling growth has important repercussions for offspring fitness in avian populations and may be affected by microbial colonization of the gut. Enterococcus faecalis is a common opportunistic pathogen, whereas E. faecium has been used as a growth promoter because it interacts competitively with pathogenic bacteria, E. faecalis included. We followed the growth in tarsus length and mass of 18 Pied Flycatcher (Ficedula hypoleuca) broods. Chicks were weighed and measured on days 4, 8, 10, and 13 after hatching. On day 13, wing length was also measured and cloacal swabs were taken of two chicks in each brood for detection of enterococci. In all, the methods used allowed us to detect six species of bacteria among a possibly much richer community. Most chicks had E. faecalis, whereas E. faecium was less prevalent. There was a negative association between scores for E. faecalis and for the rest of the species pooled. The presence of E. faecalis showed no detectable association with nestling mass or size at any age, whereas the presence of the other species showed significantly positive associations with mass and size on day 13, but not before. Presence of E. faecium on its own was positively associated with nestling mass and size shortly before fledging. E. faecium may act as a growth promoter in the wild through its competitive interactions with facultative pathogenic bacteria. The presence of some microbes are critically important in avian growth and development.

I studied the characteristics of foraging territoriality in the Little Egret (Egretta garzetta) and effects of body size and sex on territoriality. Sixty-eight birds were captured and sexed, and foraging behavior (usage of area, defense rate, and foraging efficiency) of 26 birds identified by color bands was observed in detail for 3 years. I categorized territoriality within the foraging area into three types according to the birds' exclusiveness and attachment to the area: high exclusiveness and strong attachment to the same area for a long period, moderate exclusiveness and attachment, and minimal exclusiveness and attachment. Body size was largest and feeding efficiency was highest in the first type. I propose a model that predicts a relationship between body size and defense rate to explain the behavior of egrets.

Habitat edges are well-studied components of fragmented landscapes, yet factors mediating edge effects remain unclear. We report how different types of edges surrounding patches may affect spatial distributions of Bobolink (Dolichonyx oryzivorus), a declining, area-sensitive songbird that breeds in grasslands. We expected Bobolinks to be less abundant near edges, and we investigated a set of alternative hypotheses for explaining that spatial pattern: (1) passive displacement, in which individuals do not avoid edges but use edges as boundaries for territories; (2) habitat gradients, in which individuals respond to habitat structure gradients near edges; (3) territory size, in which size of territories increases near edges; and (4) active avoidance, in which individuals actively avoid edges by positioning territory boundaries away from edges. To examine those hypotheses, we surveyed Bobolinks in grassland habitats near 34 edges of three different edge types (agriculture, road, and woodland) in northern Iowa, 1999–2000. Bobolink density was lower near woodland edges than near other edge types, and density increased as a function of distance from edge for all edge types. There was no evidence for a habitat gradient close to edges, but there was some evidence for habitat structure differing among edge types. Territory size increased near roads, decreased near woodlands, but did not change near agricultural edges. Territory positioning was consistent with active avoidance near woodland edges, and to a lesser extent road edges, but positioning was only consistent with passive displacement near agriculture edges. We conclude that land use surrounding patches can have variable effects on territorial dynamics and habitat use of this area-sensitive species. Linking edge avoidance with fitness is needed to understand the demographic consequences of those responses for species in fragmented landscapes.

Survival of Brown Boobies (Sula leucogaster) at Johnston Atoll was examined over a 17-year period using capture-mark-recapture analysis. Annual adult survival was estimated to be 0.90 ± 0.01 (SE). Variation in survival did not correspond to either local environmental fluctuation or more widespread disturbances associated with El Niño-Southern Oscillation events, and a time-invariant model of survival was best supported by our data. Absence of major oceanographic anomalies in the immediate vicinity of Johnston Atoll may contribute to relatively high and invariant survival in Brown Boobies.

I investigated the effect of mass and date of departure of Ancient Murrelet (Synthliboramphus antiquus) chicks reared at two colonies in Haida Gwaii, British Columbia, on aspects of their adult biology. Chicks were captured, banded, and weighed while departing from their natal colony at two to three days old, during 1984–1998. Adults were recaptured at the same colonies during the breeding seasons of 1986–2000. Just under 1% of 13,055 chicks were recaptured as adults. Chicks that were heavier than average at colony departure were recaptured as adults at a younger age and were heavier as breeders than lighter chicks. However, chick departure mass did not affect adult mass of birds recaptured as nonbreeders. The date at which chicks left the colony had no effect on either adult mass or age at recapture. Correlation between chick mass at colony departure and adult mass as a breeder is rarely reported and is difficult to explain. However, if chick mass is determined by reproductive investment on the part of the parents and adult mass is a measure of reproductive investment by the individual, the correlation suggests that degree of parental investment could be a heritable trait.

It has proven difficult to support the classic prediction of aerodynamic theory that highly migratory birds should have more pointed wings than less migratory birds. This study extends the search by testing for correlations between wing shape of Calidris sandpipers and a traditional migratory variable (total migration distance) as well as a novel variable (relative fuel load). Using phylogentically independent contrasts, it was determined that relative fuel load is a better predictor of wing shape than total migration distance.

We analyzed distribution of Hermit Thrushes (Catharus guttatus faxoni) wintering in the eastern United States and northeastern Mexico using data from 2,077 specimens collected in winter or during migration. Hermit Thrushes collected in winter showed a sex-biased latitudinal distribution, with the female mean 1.2° south of the male mean. Three general, nonmutually exclusive hypotheses have been proposed to account for that pattern in other species: (1) dominance of males over females, which forces females to lower latitudes; (2) larger body size of males, which permits males to overwinter in colder areas; and (3) earlier arrival by males on breeding grounds, which selects for males to winter closer to the breeding grounds. The dominance hypothesis requires that females be subordinate, an assumption that is not supported by previous research with wintering Hermit Thrushes. We also found no difference in sex ratio among habitats, despite strong differences in habitat quality. The body-size hypothesis requires that the larger sex be able to withstand colder temperatures. Male Hermit Thrushes are larger, but neither multiyear climate data nor weather in the specific month and year when birds were collected showed males to face significantly colder temperatures on the wintering grounds. Our data are most consistent with the arrival-time hypothesis. Males collected during spring migration migrated ∼20 days before females. When males began migrating in March, they experienced colder weather than sedentary females. By wintering farther north and migrating earlier, males expedite their return to their breeding grounds, although the small difference in winter distribution between the sexes is marginal compared to the effect of males’ much earlier departure. Presumably, any cost to males of wintering or migrating under more demanding conditions is balanced by the advantage of early arrival on the breeding grounds.

New World orioles (Icterus) include several closely related species and subspecies pairs that provide excellent opportunities for studying recent speciation. We examined a subspecies pair in the Orchard Oriole group: Orchard Oriole (I. spurius spurius), a long-distance migrant that breeds in eastern North America, and Fuertes’s Oriole (I. s. fuertesi), a short-distance migrant that breeds in a restricted range in Veracruz, Mexico. We sequenced parts of the mitochondrial cytochrome-b gene (925 base pairs) and control region (344 base pairs) from 23 Orchard Orioles and 7 Fuertes’s Orioles. Subspecies are not reciprocally monophyletic. Instead, our data suggest that at least one taxon is paraphyletic or polyphyletic. We found little support for any further phylogenetic structure, including whether one subspecies might be derived from the other. However, haplotype frequency analysis suggests that there is little or no current gene flow between the taxa. The phylogenetic relationship between Orchard and Fuertes’s orioles is likely a result of recent divergence and incomplete lineage sorting. That interpretation is consistent with theoretical models of speciation, which predict patterns of nonmonophyly at early stages of taxon divergence. Our findings suggest that Orchard and Fuertes’s orioles are separate species and provide a case study for evaluating the importance of monophyly in defining species limits.

Egg-capping is the slipping of a hatched eggshell fragment over an intact shell. It is a rare phenomenon among avian species, probably because most eggs in the same clutch hatch synchronously, are similar in size, and parents typically remove debris—including shell fragments—from nests. Hatching asynchrony and egg-size differences are typically more pronounced in the context of interspecific brood parasitism, making conditions for egg-capping more likely. Indeed, egg-capping of host eggs occurred in 33% of clutches of Eastern Phoebes (Sayornis phoebe) parasitized by Brown-headed Cowbirds (Molothrus ater), always by the earlier hatched cowbird's eggshell, whereas it was not detected in nonparasitized clutches near Ithaca, New York. To determine experimentally if host parents rejected their own eggs capped by the parasite's shell, cowbird shell fragments were introduced into nonparasitized phoebe clutches either as slipped over intact phoebe eggs (caps) or simply placed into the nests (noncaps). The latency for cowbird egg-fragments to disappear was greater for caps (1–13 days) because all noncaps were removed in <1 day. Whether phoebe eggs hatched was also related to the outcome of the capping treatments: eggs that remained capped for >1 day had a greater probability of hatching failure (0.6) than noncapped eggs (0). Those data suggest that egg-capping by shell-fragments of earlier hatched cowbird eggs reduces phoebes' reproductive success and may represent a fitness cost to hosts in other parasitized species as well.

Molting females of Monteiro's Hornbills (Tockus monteiri) seal themselves in nest cavities to breed until chicks are about half grown. To gain insight into the chronology of energy requirements of the Monteiro's Hornbill family unit in relation to this peculiar breeding strategy, we measured a number of ecological, physiological, and environmental variables during the Monteiro's Hornbill's breeding season. Those measurements included rates of energy expenditure of female Monteiro's Hornbills while in the nest cavity, characterizing their thermal environment, timing of egg laying, molt, hatching and fledging of chicks, as well as measuring clutch size and chick growth. Temperatures within the nest box varied between 12 and 39°C and did not affect the female energy expenditure. Female body mass and energy expenditure averaged 319 g and 5 W, respectively, at the start of concealment and decreased by on average 1.1 g day⁻¹ and 0.05 W day⁻¹ during at least the first 30 days of the 52–58 day concealment period. Clutch size varied between 1 and 8 and averaged 4.1 eggs, with eggs averaging only 66% of the mass predicted for a bird of this size. Over the range of chick ages at which the female might leave the nest, the predicted energy requirements for maintenance and tissue growth for a Monteiro's Hornbill chick increase sharply from 1.2 W at age 8 to 3.0 W at age 25. Reduction of the female energy requirement with time, the relatively low growth rate and therewith low energy requirements of Monteiro's Hornbill chicks, and an appropriate timing of the female's exodus from the nest cavity all aid in containing peak energy demands to levels that are sustainable for the food provisioning male.

Prescribed burning is increasingly being used to restore and maintain oak-dominated (Quercus spp.) forests in the eastern United States. We assessed effects of prescribed burning on the nesting ecology of the Wood Thrush (Hylocichla mustelina). Recent declines in Wood Thrush populations have prompted concern about their conservation status. Low-intensity surface fires in mixed-oak forests resulted in reductions in midstory vegetation, a documented habitat requirement for Wood Thrushes, but local population levels of Wood Thrushes did not differ between burned and unburned areas. Wood Thrushes inhabiting recently burned areas selected nest sites where leaf litter cover, fern cover, densities of shrubs and saplings, and moisture levels were higher and where fire intensity was lower in comparison to random sites. Wood Thrushes also placed their nests higher off the ground, and in taller and larger-diameter trees and shrubs, in burned than in unburned areas. Reproductive success did not differ between burned and unburned areas. However, successful nests were placed higher off the ground and in areas with lower densities of shrubs and saplings than unsuccessful nests in both burned and unburned areas. Prescribed burning appeared to have minimal effects on nesting ecology of Wood Thrushes, given their flexibility in nest placement, with no adverse consequences in terms of reproductive success. Local variation in fire intensity and moisture levels also maintained availability of suitable nesting habitat within burned areas. Continued monitoring would be appropriate to further assess the response of Wood Thrushes to prescribed burning, particularly in consideration of their conservation status and the uncertainty associated with potential long-term effects of habitat change.

Extrapair paternity and its correlates with breeding synchrony were examined in Gadwall (Anas strepera) using microsatellite DNA fingerprinting. Eleven of 261 ducklings (4.2%) within 8 of 29 broods (27.6%) had genotypes consistent with extrapair fertilizations, a comparable frequency to other species of waterfowl for which extrapair paternity has been documented. We found no evidence of intraspecific brood parasitism. The frequency of extrapair paternity was not significantly correlated with breeding synchrony. We suggest that female absences during egg-laying may have provided males with opportunities to pursue extrapair copulation when breeding was synchronous.

Using molecular genetic markers that differ in mode of inheritance and rate of evolution, we examined levels and partitioning of genetic variation for seven nominal subspecies (11 breeding populations) of Canada Geese (Branta canadensis) in western North America. Gene trees constructed from mtDNA control region sequence data show that subspecies of Canada Geese do not have distinct mtDNA. Large and small-bodied forms of Canada Geese were highly diverged (0.077 average sequence divergence) and represent monophyletic groups. A majority (65%) of 20 haplotypes resolved were observed in single breeding locales. However, within both large and small-bodied forms certain haplotypes occurred across multiple subspecies. Population trees for both nuclear (microsatellites) and mitochondrial markers were generally concordant and provide resolution of population and subspecific relationships indicating incomplete lineage sorting. All populations and subspecies were genetically diverged, but to varying degrees. Analyses of molecular variance, nested-clade and coalescencebased analyses of mtDNA suggest that both historical (past fragmentation) and contemporary forces have been important in shaping current spatial genetic distributions. Gene flow appears to be ongoing though at different rates, even among currently recognized subspecies. The efficacy of current subspecific taxonomy is discussed in light of hypothesized historical vicariance and current demographic trends of management and conservation concern.

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