When feather-degrading Bacillus licheniformis is grown in culture, it secretes a keratinase that hydrolyzes the β-keratin matrix of a feather, thereby releasing oligopeptides that dissolve into the medium surrounding the feather and feather-degrading bacilli. These peptides absorb light passed through a sample of medium from which feather fragments, melanin granules, and bacteria have been removed by centrifugation. Samples of medium in which white, nonmelanic feathers are degrading absorb more light than samples of medium in which black, melanic feathers are degrading, which indicates that more oligopeptides are dissolved in medium surrounding white feathers than in medium surrounding black feathers. The differential absorption of light supports the conclusion that B. licheniformis degrades white feathers more rapidly than black feathers.

The double-collared sunbirds of the Eastern Arc Mountains of Tanzania and southeastern Kenya are characterized by regional variation in morphology and plumage. That variation has resulted in considerable dispute over their taxonomic status and delineation of range boundaries. It has been suggested that Moreau's Sunbird (Nectarinia Moreaui) is an atypical phenotype that has arisen from a hybridization event between the more widely distributed Eastern Double-collared Sunbird (N. mediocris) and the narrowly distributed Loveridge's Sunbird (N. loveridgei). A discriminant analysis of six standard morphological characters indicates that Moreau's Sunbird is intermediate in shape and size between the Eastern Double-collared and Loveridge's sunbirds. There is greater overlap between female Moreau's and Eastern Double-collared sunbirds than between males; Loveridge's Sunbird shows little overlap with the other taxa. Discrete plumage characters separate all three taxa. Molecular analyses of 728 base pairs of mitochondrial DNA (NADH3 and control region) suggest that Moreau's Sunbird is a valid taxon and the sister species to Loveridge's Sunbird. Eastern Double-collared Sunbird haplotypes can be divided into three distinct clades, separated from each other by substantial genetic divergence (approximately 8–10% sequence divergence). We propose species status for each of those clades and suggest the following three taxa: N. mediocris Shelley 1855, N. usambarica Gröte 1922, and N. fuelleborni Reichenow 1899. Finally, we propose a biogeographical hypothesis of speciation events within the N. mediocris species complex.

The curassows comprise 14 species of sedentary Neotropical birds classified in four genera (Crax, Nothocrax, Mitu, and Pauxi) in the family Cracidae. Congeneric species have a striking pattern of allopatric distributions that might be attributable to vicariance, dispersal, or a combination of the two. To test those biogeographic hypotheses, a strongly supported phylogeny was needed, so that existing problems of taxonomic rank could be solved and a better understanding of the group's evolutionary history attained. We therefore estimated the phylogenetic relationships of all 14 species, on the basis of 6,929 sites of six different mitochondrial DNA regions, and reassessed the status of the four genera. Sequences from the ND4 gene favored a tree that was highly incongruent with the tree recovered using the other five gene regions. However, when the ND4 sequences were concatenated with the sequences of the other genes, the optimal phylogeny was unchanged from that derived for the other genes. That combined tree was divided into two well-supported clades: one containing the seven species of Crax and the other containing the monospecific genus Nothocrax, as sister to a clade of the Mitu and Pauxi species. Mitu and Pauxi are not reciprocally monophyletic, which appears to be attributable to a distant hybridization event and a transfer of Mitu mtDNA into P. unicornis. We estimated divergence times; the diversification of curassow seems to have occurred from the Middle Miocene to the end of the Pliocene (9.5 to 1.6 Ma). Vicariance—following marine transgressions, the rise of the Andes, and subsequent changes in river basins in South America—seems to be the major mode of isolation that favored allopatric speciation in the group.

We investigated patterns and causes of variation in clutch sizes in a guild of five species of temperate-nesting dabbling ducks (Mallard [Anas platyrhynchos], Northern Pintail [“pintail,” A. acuta], Gadwall [A. strepera], Blue-winged Teal [“teal,” A. discors], and Northern Shoveler [“shoveler,” A. clypeata]) during 1993-1995 in the Prairie Pothole Region of midcontinental North America. Clutch sizes (mean ± SE) were largest for teal (10.80 ± 0.03), followed in descending order by those of shoveler (10.31 ± 0.05), Gadwall (9.92 ± 0.04), Mallard (8.91 ± 0.04), and pintail (7.66 ± 0.06). In Mallard, pintail, and shoveler, predicted clutch sizes at onset of nesting exhibited minimal variation. Clutch sizes of Gadwall and teal displayed statistically significant variation among years at onset of nesting; pintail clutch sizes showed significant variation late in the nesting season. Clutch sizes declined seasonally in all species. Declines in clutch sizes of teal and shoveler were approximately linear; whereas clutch sizes of Mallard, pintail, and Gadwall usually declined at progressively decreasing rates. Linear declines in teal and shoveler clutches suggest that those species experienced greater difficulty securing lipids for egg production late in the nesting season than did Mallard, pintail, and Gadwall. That disparity may result because egg-laying female teal and shoveler feed almost exclusively on animal foods, which are primarily protein; whereas female Mallard, pintail, and Gadwall consume more carbohydrate-rich plant foods. Our findings, when examined in context with existing information, suggest that interspecific variation in clutch sizes results from innate differences in several traits—including body size, diet, timing of lipid acquisition, and nesting—all of which can affect the amount of lipid available for egg production. Temperate-nesting dabbling ducks have evolved traits that facilitate laying of large clutches early in the nesting season, because risk of mortality is lower among early-hatched young. Annual differences in clutch sizes of all five species were not significant when effects of annual variation in nest-initiation dates were accounted for, reflecting the key role of environmental influences on intraspecific variation in clutch sizes among years.

Mayfield logistic regression is a method for analyzing nest-survival data that extends the traditional Mayfield estimator by incorporating explanatory variables (e.g. habitat structure, seasonal effects, or experimental treatments) in a logistic-regression analysis framework. Although Aebischer (1999) previously showed that logistic regression can be used to fit Mayfield models, few ornithologists have put that finding into practice. My purpose here is to reintroduce this underused method of nest-survival analysis, to compare its performance to that of a dedicated survival-analysis program (MARK), and to provide a practical guide for its use. Like the traditional Mayfield method, Mayfield logistic regression accounts for the num ber of “exposure days” for each nest and allows for uncertain fates (censoring), thus avoiding the bias introduced by typical applications of logistic regression. Mayfield logistic regression should be widely applicable when nests are found at various stages in the nesting cycle and multiple explanatory variables influencing nest survival are of interest.

The relationship between health and demography in the Green-rumped Parrotlet (Forpus passerinus) was examined, using hematological measurements as indicators of health. Variation in adult hematology with gender, age, time during nesting cycle, and breeding status were examined. Only gender and time during nesting cycle showed significant effects on hematology. Females had higher white-blood-cell counts and immunoglobulin-G (IgG) levels than males. Hematocrit was lower during egg laying than at other stages for females, whereas white-blood-cell counts and IgG and alpha-2-macroglobulin (α₂m) levels were higher. In males, IgG and α₂m levels were higher during egg laying. We expected that hematological indicators of health would predict reproductive success. Some relationships were identified (α₂m was negatively related to number of fledglings in males and females, female lymphocytes were negatively related to number of eggs, and basophils were negatively related to number of fledglings) at P < 0.05. However, despite substantial sample sizes (n > 25), none of those relationships were significant after Bonferroni correction, though there appears to be a threshold level for those hematological measures, below which adults may have high or low reproductive success, but above which reproductive success will be low. We suggest that the effect of micro-rather than macroparasites may affect health, resulting in weak effects on reproductive success. Because of the transient nature of microparasitic infection, health and reproductive success may be more significantly related over an organism’s lifetime than in any given year.

We investigated factors affecting nest success of songbirds in riparian forest and buffers in northeastern Missouri. We used an information-theoretic approach to determine support for hypotheses concerning effects of nest-site, habitat-patch, edge, and temporal factors on nest success of songbirds in three narrow (55–95 m) and three wide (400–530 m) riparian forests with adjacent grassland-shrub buffer strips and in three narrow and three wide riparian forests without adjacent grassland-shrub buffer strips. We predicted that temporal effects would have the most support and that habitat-patch and edge effects would have little support, because nest predation would be great across all sites in the highly fragmented, predominantly agricultural landscape. Interval nest success was 0.404, 0.227, 0.070, and 0.186, respectively, for Gray Catbird (Dumetella carolinensis), Northern Cardinal (Cardinalis cardinalis), Indigo Bunting (Passerina cyanea), and forest interior species pooled (Acadian Flycatcher [Empidonax virescens], Wood Thrush [Hylocichla mustelina], Ovenbird [Seiurus aurocapillus], and Kentucky Warbler [Oporornis formosus]). The effect of nest stage on nest success had the most support; daily nest success for Gray Catbird and Indigo Bunting were lowest in the laying stage. We found strong support for greater nest success of Gray Catbird in riparian forests with adjacent buffer strips than in riparian forests without adjacent buffer strips. Patch width also occurred in the most-supported model for Gray Catbird, but with very limited support. The null model received the most support for Northern Cardinal. Riparian forests provided breeding habitat for area-sensitive forest species and grassland-shrub nesting species. Buffer strips provided additional breeding habitat for grassland-shrub nesting species. Interval nest success for Indigo Bunting and area-sensitive forest species pooled, however, fell well below the level that is likely necessary to balance juvenile and adult mortality, which suggests that when riparian forests are located within agricultural landscapes, the potential even for wide riparian forests with adjacent buffer strips to provide high-quality breeding habitat is severely diminished for some species.

Perception of predation risk by animals living in habitat mosaics moderates movement behaviors, potentially influencing the connectivity of landscapes. Perception of risk varies with environmental factors, which opens the possibility of managing connectivity for animals in fragmented landscapes. Observing understory forest birds wintering in north-central Florida, we tested the hypothesis that the presence of the Tufted Titmouse (Baeolophus bicolor), a vigilant, socially dominant flocking species, would increase the propensity of multispecies flocks engaged in mobbing to cross forest boundaries and move into open areas. Eastern Screech-Owl (Megascops asio) calls were broadcast next to an owl model at sites within continuous oak forest habitats (control) or just outside of forest in either old-field habitats with clustered saplings and shrub cover (shrub treatment) or in early successional habitats (open treatment; 11 trials in each habitat). In both treatments (forest adjacent to open or shrub), models were positioned 15 m from forest boundaries in nonforest habitat. For each individual responding to the playback (i.e. that entered a 30-m radius around the model), we recorded the species and its proximity to the model using three distance classes: within 15 m (at the forest edge), 10 m (out in the open), and 1 m (at the model). Both greater vegetative cover and presence of titmice were significantly correlated with proportion of responding individuals and species that approached and crossed forest boundaries, and the effects were additive. We show experimentally that socially dominant titmice can facilitate forest-boundary crossing by other bird species, which suggests a potential mechanism defining connectivity in fragmented landscapes for wintering forest birds.

Phylogenetic relationships within the genus Cinclodes, a group of South American furnariids, were studied using complete sequences of the mitochondrial genes COII and ND3. The 13 species of Cinclodes formed a monophyletic group consisting of three major lineages: (1) the southeastern Brazilian isolate C. pabsti, which was sister to the rest of the genus; (2) a clade of five primarily Patagonian or central Argentine highlands species; and (3) a clade of seven primarily north-central Andean or Pacific species. Biogeographic structure in the Patagonian-Andean taxa was consistent with the deep Patagonian and north-central Andean division previously noted in the similarly distributed genus Muscisaxicola. Evolutionary relationships among Cinclodes species were partially consistent with expectations based on plumage, behavior, and ecology. The phenotypically distinctive C. antarcticus was found to be sister to the widespread C. fuscus in the primarily Patagonian-Argentine clade, and the distinctive C. palliatus to be sister to C. atacamensis in the high Andean-Pacific clade. The central Argentine isolates C. comechingonus and C. olrogi formed a clade with C. oustaleti (olrogi sister to oustaleti, and comechingonus sister to those two) within the Patagonian-Argentine clade. The Pacific marine specialists C. nigrofumosus and C. taczanowskii were sisters within the Andean-Pacific clade and were distantly related to the southern maritime species C. antarcticus. Thus, marine ecological specialization apparently evolved twice within Cinclodes; behavioral and ecological data also support the nonhomology of the two character states. The two exclusively Pacific species were positionally apomorphic within the Andean-Pacific clade; ancestral area analysis indicated that the high Andes were the most likely area of origin for this clade, and that the Pacific coast was occupied secondarily.

Avoidance of habitat edges may be contributing to reduced densities of grass-land birds in small habitat patches. Nest densities for grassland-nesting Bobolinks (Dolichonyx oryzivorus) were much lower than expected within 25 m of forest edges at three sites in New York, and that pattern (“edge avoidance”) extended to 100 m at one site. Nests located within 50 m of forest or wooded hedgerow edges had lower daily survival rates, compared with nests ≥100 m from any habitat edge. Bobolinks tended to move away from forest edges when renesting after nest failure; that pattern was especially evident in females that placed their first nest within 50 m of a forest or wooded hedgerow edge. Second nests of all seven of those females were farther from that edge type than their first nests. However, nest placement in relation to wooded edges did not vary significantly between years for those philopatric females nesting at our study sites for more than one year. Bobolinks also avoided nesting near road edges, even though nest survival rates were not lower near that edge type. However, Bobolinks did not appear to avoid nesting near edges adjacent to old fields or pastures. Nest survival near those edge types was higher than near wooded edges and similar to or higher than survival of nests ≥100 m from any edge. Thus, responses of Bobolinks to habitat edges were inconsistent, and nest success was dependent on type of edge.

Incubation is an energetically demanding process for parents, in part because of the thermodynamic costs of maintaining egg temperature. One might predict that aspects of nest construction—in particular, the thermodynamic properties of the nesting material and the degree to which the nest provides shelter from the wind—would have important effects on thermodynamic costs. However, little is known about the relative importance of those factors. Here, we investigate egg cooling rates in several commonly used nesting materials and in various wind speeds and examine the effect on those rates of wetting the materials. Nesting materials differ greatly in their insulating properties; feather down is the best insulator, and grass the worst. When the materials are wet, eggs cool much more rapidly, differences between materials tend to diminish, and down becomes the worst insulator. Hence, there may be significant selection pressure to choose particular nesting materials, but materials may be better or worse according to the situation of the nest. Increasing wind speed also has profound effects on egg cooling rates, even at the low speeds tested here, which implies strong selection pressure to locate and construct nests that minimize wind speed at the egg surface. Our results suggest that nest construction may have an important bearing on the subsequent costs of reproduction, and that important trade-offs may exist between nest construction for reduced thermodynamic costs, and other costs and benefits of nest-building and reproduction.

A monogamous mating system that includes extrapair fertilization can potentially generate higher variability in male reproductive success than monogamy without extrapair fertilization. That increased variability could provide a correspondingly higher opportunity for sexual selection and, thus, for the origin and persistence of sexual dimorphism in monogamous species. To determine whether extrapair fertilization enhanced the opportunity for sexual selection in a sexually dimorphic, monogamous bird species, we used microsatellite DNA typing to assess the prevalence of extrapair fertilization and its effect on variation in male reproductive success in a population of Chestnut-sided Warblers (Dendroica pensylvanica). We found that the level of extrapair fertilization in our study population was at the upper end of the range reported for bird populations (47% of nestlings had extrapair fathers; 61% of broods contained extrapair offspring). We also discovered that almost all extrapair offspring were sired by paired males resident on nearby territories. In addition, we found that variation in male reproductive success was substantially higher than variation in female reproductive success, and that extrapair fertilizations made a significant contribution to variation in male reproductive success. Together, those findings suggest that extrapair fertilization creates an opportunity for sexual selection on male traits in this population.

Annual fecundity is a demographic parameter that is elemental to population biology, but accurate measures of fecundity are rarely obtained. We used radiotelemetry to follow female Eastern Meadowlarks (Sturnella magna) throughout the 1999-2000 breeding seasons in southeastern Illinois to estimate their annual fecundity and assess if the outcome of initial nesting attempts affected site selection for subsequent nests. Thirty-four females built 52 nests (1.53 ± 0.12 nests female⁻¹), but only 21 females (62%) fledged young. Only 44% of females renested at the study site, and more females (53%) emigrated after successfully fledging young from an initial nest than after failing in their first attempt (21%). Nest-site characteristics were similar between successful and failed nests for both initial and subsequent attempts. Females that failed during first attempts did not change nest characteristics for renests. Given that few females were double-brooded and that unsuccessful females did not persistently renest, annual fecundity for females nesting at the study site was between 1.27 ± 0.38 and 1.36 ± 0.37 female young year⁻¹. On the basis of our fecundity measure, we estimated that annual adult survival of 59–61% was necessary for maintenance of a stable population (λ = 1.0). Failure of most females to attempt to raise two broods suggests that double brooding carries substantial costs for meadowlarks.

We summarized records of hybridization between Barred Owls (Strix varia) and Northern Spotted Owls (S. occidentalis caurina) in Washington and Oregon through 1999. A total of 47 hybrids were observed, including 17 F1s that were first detected as adults, 4 F1s that were banded as juveniles and subsequently recaptured as adults, 10 F1 juveniles, and 16 F2 juveniles. All confirmed cases of hybridization between Barred and Spotted owls involved male Spotted Owls paired with female Barred Owls. Ten F1 hybrids that backcrossed with Barred Owls produced a total of 15 young; 6 F1 hybrids that backcrossed with Spotted Owls produced only 1 young. Those differences may indicate that some combinations of sex and species are more compatible or more fertile than others, but more documentation is needed. Because F2 hybrids and subsequent generations are difficult to distinguish in the field from Barred or Spotted owls, genetic comparisons of blood or tissue samples may be needed to identify hybrids beyond the first generation. The small number of F1 hybrids detected during many years of extensive banding studies of Spotted Owls suggests that the isolating mechanisms that separate Barred and Spotted owls are normally sufficient to avoid hybridization between them. Direct competition between the two species for food and space is probably a much more serious threat to the Spotted Owl than hybridization.

The breeding biology of Rainbow Bee-eaters (Merops ornatus) was studied between 1997 and 2001 in southeast Queensland, Australia. Rainbow Bee-eaters are unusual in that they combine migration and coloniality with cooperative breeding. Birds migrate from islands north of Australia to build nests either solitarily or in colonies containing ≤50 active nests that are attended by socially monogamous pairs or trios (45% of nests). Nesting was essentially forsaken during very dry seasons, whereas hatching success was reduced in wet seasons. Incubation period varied in duration, with chicks emerging 22–31 days after incubation commenced. Eggs hatched either synchronously or, more commonly, asynchronously (88% of clutches), with each chick emerging usually 0–3 days after the previous hatchling in the nest. Asynchronous hatching typically led to a marked size hierarchy within the brood, facilitating starvation of 22% of nestlings that had avoided nest disasters, such as predation or flooding. Duration of the nestling period was also variable, with chicks requiring a further 24–36 days to fledge. Nest predation by native predators—monitor lizards (Varanus varius) and yellow-footed antechinus (Antechinus flavipes)—was relatively low, affecting 10% of nests. In contrast, predation by two introduced species—dingoes (Canis familiaris dingo) and, in particular, cane toads (Bufo marinus)—was extreme, terminating 49% of all nests.

Female songbirds generally have an innate ability to distinguish between con-specific and heterospecific song, and may learn to discriminate among variants of conspecific song. By observing female copulation-solicitation displays elicited by playback of perched songs and flight whistles from distant (>2,000 km) widespread populations, we assessed the extent to which responses of female Brown-headed Cowbirds (Molothrus ater) to the two categories of male courtship song depend on experience. We hypothesized that female responsiveness to flight whistles is more dependent on experience than their responsiveness to perched song, because, though both perched songs and flight whistles vary spatially, perched songs always conform to strict species-specific structural and syntactic rules. Flight whistles, in contrast, are so variable that some types may not be recognizable as conspecific vocalizations to birds that have never experienced them. The species-wide structural similarities of perched songs make it possible for females to have innate responsiveness to these songs, as shown by isolate-reared females. In contrast, isolate-reared females do not respond to flight whistles. In the present study, females readily responded to foreign perched-song types, but showed as little response to foreign flight whistles as they did to heterospecific control songs. A previous study had shown that the same females were highly responsive to the local flight whistle. Thus, in accord with our hypothesis, females must have direct experience with a flight-whistle type to become responsive to it, but will respond to any unfamiliar perched-song type. Our findings for females are concordant with results on variation in the role experience plays in development of male production of songs from these two categories.

Previous interspecific studies have shown that migratory birds have a higher prevalence of blood parasites than nonmigratory birds. It is thought that birds that move greater distances are exposed to a larger parasite fauna, because of uneven distribution of vectors that carry such parasites. Current hypotheses also suggest that the stress of migration may allow parasites to persist, by weakening the immune system and allowing latent infections to recur. We captured migrating hatching-year Sharp-shinned Hawks (Accipiter striatus) in New Mexico and estimated natal latitudes of each individual by analyzing stable-hydrogen isotope ratios of feathers. That enabled us to estimate distances traveled up to point of capture. We also collected blood to quantify hematozoan infection prevalence and intensity. We related distance traveled to prevalence and intensity of hematozoan infections. Contrary to previous hypotheses, our results show no relationship between distance traveled by migrants and prevalence and intensity of hematozoan infections. Of 75 individuals examined, 24% were infected with Leucocytozoon toddi, 37% with Haemoproteus elani, and 5% with H. janovyi. To our knowledge, this is the first documented occurrence of H. janovyi in North America and in Sharp-shinned Hawks. Our stable-hydrogen isotope analyses indicated that H. janovyi was detected only in birds that originated in southwestern North America, which may be of significance in regard to biogeography of that parasite species.

A molecular phylogeny based on 917 base pairs (bp) of the mitochondrial (mt) DNA cytochrome-b gene was used to test and reassess the systematics and conflicting taxonomic treatments of the small, black-and-white Puffinus shearwaters, including the P. assimilis-lherminieri species complex. Three geographically discrete clades were identified in the North Atlantic, Southern (Australasia) and tropical Pacific and Indian oceans that contain most of the P. assimilis-lherminieri taxa. Together with four other lineages (P. puffinus, P. opisthomelas, P. mauretanicus-P. yelkouan, P. newelli-P. myrtae), they form an unresolved polytomy. Puffinus huttoni-P. gavia, P. nativitatis, and P. subalaris are basal to this. The phylogenetic positions of P. myrtae and P. subalaris are unexpected and warrant further investigation. None of the competing taxonomic treatments of the P. assimilis-lherminieri complex are supported. Instead, our phylogeny suggests that 14 taxa should be recognized, whereas five others (loyemilleri, colstoni, nicolae, polynesiae, and atrodorsalis) are phylogenetically undifferentiated from more widespread species (lherminieri, dichrous, and bailloni) and are probably not valid. Similarities in plumage and external morphological characters between unrelated species and differences between closely related species suggest that those traditional taxonomic characters are poor indicators of phylogenetic relatedness.

For point-count data to reliably index bird abundance or density, estimates must be corrected for variation in detection probabilities across species, observers, and environmental conditions. Removal and double-observer modeling are two recently developed statistical techniques for estimating detection probabilities and bird abundance. We collected point-count data in north-central Indiana and used a Huggins closed-capture model in MARK to directly compare those two methods. We found that when detection probabilities were relatively high for individual observers, the two methods yielded similar estimates of density for nearly all 17 species modeled. However, when true detection probabilities for observers were relatively low, removal estimates of detectability and density were biased high and low, respectively, perhaps because of the effect of low-detection probability on the removal estimator or smaller sample sizes associated with less-skilled observers. In general, we consider removal modeling a more desirable approach than double-observer modeling because it requires half as many observers, allows more sources of variation in detectability to be modeled, and estimates abundance or density of the true population of birds. By contrast, double-observer modeling estimates only the abundance of the “apparent” population (i.e. those birds that are visually or audibly conspicuous). For species that vocalize infrequently or are otherwise elusive, the apparent population may be significantly smaller than the true population. However, double-observer modeling is more robust to violations of the assumption of population closure and may outperform removal methods when data are collected by less-experienced observers.

Animals often exhibit territorial spatial structure in their breeding habitat. This clustering behavior is not well understood. We reviewed eight hypotheses for clustering and tested two ecological hypotheses for the formation of dense, territorial clusters in the Least Flycatcher (Empidonax minimus), a socially monogamous forest bird. The material resources hypothesis suggests that clustering is a response to habitat heterogeneity in vegetation, food, or both. The predation hypothesis proposes that clustering may reduce nest predation. Univariate and multivariate analyses of 170 vegetation plots from 1997 to 1998 indicated that forest-stand structure and tree species composition could not explain clustering in our population (predictions 1–3). Comparison of mean arthropod biomass inside with arthropod biomass outside two clusters sampled in 1999 using Malaise traps revealed that potential food resources were also unrelated to clustering (prediction 4). Nest predation rates were not correlated with territory position in clusters or with cluster size. In addition, predation rates were similar for clustered and solitary pairs (predictions 5–7). We conclude that habitat characteristics and nest predation do not explain clustered breeding in Least Flycatchers, though further tests of those hypotheses would be helpful. We develop the idea that the pursuit of extrapair copulations may promote clustered breeding. Future studies of territorial spatial structure in Least Flycatchers and other species should consider explanations based on mating behavior concomitant with ecological explanations for clustering.

Survival rate from fledging to breeding, or juvenile survival, is an important source of variation in lifetime reproductive success in birds. Therefore, determining the relation-ship between juvenile survival and environmental factors is essential to understanding fitness consequences of reproduction in many populations. With increases in density of individuals and depletion of food resources, quality of most habitats deteriorates during the breeding season. Individuals respond by dispersing in search of food resources. Therefore, to understand the influence of environmental factors on juvenile survival, it is also necessary to know how natal dispersal influences survival of juveniles. We examined effects of various environmental factors and natal dispersal behavior on juvenile survival of endangered Snail Kites (Rostrhamus sociabilis) in central and southern Florida, using a generalized estimating equations (GEEs) approach and model selection criteria. Our results suggested yearly effects and an influence of age and monthly minimum hydrologic levels on juvenile Snail Kite survival. Yearly variation in juvenile survival has been reported by other studies, and other reproductive components of Snail Kites also exhibit such variation. Age differences in juvenile survival have also been seen in other species during the juvenile period. Our results demonstrate a positive relationship between water levels and juvenile survival. We suggest that this is not a direct linear relationship, such that higher water means higher juvenile survival. The juvenile period is concurrent with onset of the wet season in the ecosystem we studied, and rainfall increases as juveniles age. For management purposes, we believe that inferences suggesting increasing water levels during the fledging period will increase juvenile survival may have short-term benefits but lead to long-term declines in prey abundance and possibly wetland vegetation structure.

The Rufous-crowned Sparrow (Aimophila ruficeps) is a nonmigratory passerine that displays an area-sensitive distribution pattern of abundance in fragmented coastal sagescrub habitat of southern California. To determine if habitat fragmentation negatively affected adult survival, we used Cormack-Jolly-Seber models to compare annual survival probabilities of adult sparrows breeding in habitat adjacent to urban-developed edges to those of birds breeding in the interior of large habitat expanses in San Diego County, 1997–2000. During that period, an El Niño event brought heavy rainfall to the study area, and a La Niña event brought drought. Annual survival probabilities were relatively high for a small passerine (females: 0.69 ± 0.05 SE; males: 0.74 ± 0.04 SE) but, given our data, did not differ between habitat types or with rainfall. Annual resighting probabilities for the birds were strongly associated with variation in rainfall, being high in the wet year and low in the dry year. Mate- and site-fidelity were apparently high, and surveys during the nonbreeding season documented that the sparrows stayed paired and on territories year-round. We hypothesize that the high apparent survivorship of this species is related to its nonmigratory habit and its tendency to curtail reproductive effort during periods of food scarcity. Although our survivorship analysis suggests that the urban-wildland interface does not adversely affect survival of territorial Rufous-crowned Sparrows, our power to detect an effect of habitat edge on survival was low. Thus, we urge caution in concluding that edge effects do not have an ecologically important influence on survival rates in this species.

The continental scaup population (Lesser [Aythya affinis] and Greater [A. marila] combined) has declined markedly since 1978. One hypothesis for the population decline states that reproductive success has decreased because female scaup are arriving on breeding areas in poorer body condition than they did historically (i.e. spring condition hypothesis). We tested one aspect of that hypothesis by comparing body mass and nutrient reserves (lipid, protein, and mineral) of Lesser Scaup at four locations (Louisiana, Illinois, Minnesota, and Manitoba) between the 1980s and 2000s. We found that mean body mass and lipid and mineral reserves of females were 80.0, 52.5, and 3.0 g higher, respectively, in the 2000s than in the 1980s in Louisiana; similarly, body mass and lipid and mineral reserves of males were 108.8, 72.5, and 2.5 g higher, respectively. In Illinois, mean body mass and lipid reserves of females were 88.6 and 56.5 g higher, respectively, in the 2000s than in the 1980s; similarly, body mass and lipid and mineral reserves of males were 80.6, 76.0, and 2.7 g higher, respectively. Mean body mass of females were 58.5 and 58.9 g lower in the 2000s than in the 1980s in Minnesota and Manitoba, respectively; mean body mass of males, similarly, were 40.7 g lower in Minnesota. Mean lipid reserves of females in the 2000s were 28.8 and 27.8 g lower than those in the 1980s in Minnesota and Manitoba, respectively. Mean mineral reserves of females in the 2000s were 3.2 g lower than those in the 1980s in Manitoba. Consequently, females arriving to breed in Manitoba in the 2000s had accumulated lipid reserves for 4.1 fewer eggs and mineral reserves for 0.8 fewer eggs than those arriving to breed there in the 1980s. Accordingly, our results are consistent with the spring condition hypothesis and suggest that female body condition has declined, as reflected by decreases in body mass, lipids, and mineral reserves that could cause reductions in reproductive success and ultimately a population decline.

The Eastern Spot-billed Duck (Anas zonorhyncha) historically was rare in the southern Russian Far East. However, during the last 60–70 years, its breeding range in East Asia has expanded northwest; Eastern Spot-billed Ducks are breeding increasingly within the range of Mallards (A. platyrhynchos). We collected 120 Eastern Spot-billed Ducks and Mallards from Primorye, Russia, and sequenced 666–667 base pairs (bp) of the maternally inherited mitochondrial DNA (mtDNA) control region and 255 bp of the ornithine decarboxylase intron six (ODC6). Control region and ODC-6 allele sequences revealed two divergent groups of haplotypes and alleles that differ by 1.5% and 2.0%, respectively, and correspond to Avise et al.'s (1990) group A and B mtDNA haplotypes. Group A mtDNA haplotypes occurred in 22 Eastern Spot-billed Ducks and 78 Asian Mallards, and group B haplotypes occurred in 14 Eastern Spot-billed Ducks and 4 Asian Mallards. Moreover, the group B haplotypes that we observed predominantly in Eastern Spot-billed Ducks (i.e. group SB) were monophyletic and diverged by 2–16 substitutions from group B haplotypes previously sequenced from 241 Mottled (A. fulvigula), American Black (A. rubripes), and Mexican ducks (A. diazi), and from North American Mallards. In contrast, type 1 and 2 ODC-6 allele frequencies for Eastern Spot-billed Ducks and Mallards did not differ, but heterozygosity for the former was greater than expected under Hardy-Weinberg equilibrium. Our analysis is the first to document the existence of two divergent haplotype and allele lineages (group A and B, type 1 and 2) in Asian mallard species and suggests that Eastern Spot-billed Ducks are more closely related to North America's Mottled, American Black, and Mexican ducks than they are to Mallards, which occur sympatrically in East Asia. Our data are consistent with the hypothesis that Eastern Spot-billed Ducks and Mallards have hybridized extensively in the Russian Far East. If so, apparent differences in group A and B mtDNA haplotype ratios, effective populations sizes, and migration rates indicate that many more male Eastern Spot-billed Ducks mated with female Mallards and more Eastern Spot-billed Ducks received ODC-6 alleles from Mallards than vice versa. We hypothesize that those differences reflect strong female natal-site fidelity and high levels of male dispersal, and that Mallards significantly outnumber Eastern Spotbilled Ducks in Primorye. Excess heterozygosity in Eastern Spot-billed Ducks (and in Mallards to a lesser extent) is probably maintained by ongoing emigration of Eastern Spot-billed Ducks and Mallards from areas of allopatry outside the Primorye region, where Eastern Spot-billed Ducks and Mallards are predicted to possesses genotypic frequencies historically diagnostic of each species.

Population surveys indicate a trend of declining abundance of scoters (Melanitta spp.) in North America. Little is known about changes in life-history traits that may be responsible for the recent population decline of White-winged Scoters (Melanitta fusca deglandi). Therefore, we studied nesting ecology of White-winged Scoters at Redberry Lake, Saskatchewan, during the summers of 2000–2001. We found 198 nests and examined nest-site selection by comparing habitat features of successful nests, depredated nests, and random sites. Discriminant function analysis differentiated habitat features—measured at hatch—of successful nests, depredated nests, and random sites; lateral (r = 0.66) and overhead (r = 0.35) concealment were microhabitat variables most correlated with canonical discriminant functions. We also modeled daily survival rate of nests as a function of year, linear and quadratic trends with nest age, nest initiation date, and seven microhabitat variables. Nest survival from a time-constant model (i.e. Mayfield nest-success estimate) was 0.35 (95% CL: 0.27, 0.43). Estimates of nest success were lower than those measured at Redberry Lake in the 1970s and 1980s. Nest survival increased throughout the laying period and stabilized during incubation, and showed positive relationships with nest concealment and distance to water and a negative relationship with distance to edge. Considering those factors, a model-averaged estimate of nest survival was 0.24 (95% CL: 0.09, 0.42). We concluded that White-winged Scoters selected nesting habitat adaptively, because (1) successful sites were more concealed than depredated sites; (2) nest sites (both successful and depredated) had higher concealment than random sites; and (3) nest sites were on islands, where success is greater than on the mainland.

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