A bush-warbler of the genus Bradypterus, known from the mountains of Taiwan since 1917, has never been formally named as a distinct taxon. Songs of the Taiwan population differ strikingly from those of its Asian congeners in being much clearer, sweeter, more piercing, and in having a very different structure of elements. Several subtle but consistent morphological differences exist between specimens from Taiwan and all named taxa, principally in bill size and shape, plumage color and reduced variability, pattern of undertail coverts, and wing formula. Therefore, the Taiwan population is best treated as a new species.

Wetlands in the western Great Basin of the United States are patchily distributed and undergo extensive seasonal and annual variation in water levels. The American Avocet (Recurvirostra americana) is one of many shorebird species that use these wetlands as breeding and migratory stopover sites and must adjust to variable conditions. We used radio telemetry to determine postbreeding, premigratory movement patterns of avocets throughout the region. In 1996 and 1997, 185 breeding adults were captured and fitted with radio transmitters at five breeding areas in Oregon, California, and Nevada. Regular aerial and ground surveys were conducted at the five main study areas from June through September, or until all avocets had left a site. Other wetlands in the western Great Basin also were surveyed by aircraft for the presence of radio-marked birds. Fifty-six percent of radio-marked avocets were still detected in the region at least eight weeks after capture. Each of these individuals was detected at an average of 2.1 lakes (range 0 to 6), with 74% found at more than one lake system. Forty radio-marked individuals moved at least 200 km between wetlands prior to migration, most of which dispersed northward. Male and female patterns did not differ significantly. Overall, movements may be associated with a prebasic molt, exploitation of a superabundant food source in northern lakes, and reconnaissance for future breeding efforts or staging sites. These results also demonstrate wide-ranging patterns of dispersal in this species and suggest a need for the consideration of large-scale habitat connectivity issues in establishing conservation strategies for shorebirds in the western Great Basin.

Many species of waterfowl form pair bonds during the nonbreeding season, yet current descriptions of mating systems and patterns of philopatry in waterfowl focus on the breeding grounds. We studied wintering Harlequin Ducks (Histrionicus histrionicus) in southwestern British Columbia to examine mating systems and philopatric behavior outside of the breeding season. The number of males at our study area was far more variable than that of females. Males that were unsuccessful in obtaining a mate were observed over a larger area than were paired males. Habitat use overlapped considerably among paired males, and no territorial boundaries were formed. Annual return rates to the nonbreeding grounds were high for both sexes (62% for females, 77% for males). Individuals not only returned to the general study area, but also to specific sections within the study area. Males that did not pair in the previous year returned to the study area in the subsequent year with the same frequency as males that had obtained mates; however, they tended to leave the study area prior to courtship. Therefore, it is possible that males return to the same wintering grounds each year to reunite with a previous mate. High levels of philopatry by both sexes allow pairs to reunite in fall, potentially increasing the benefits of philopatry for both sexes.

We examine the validity of Phalacrocorax [Stictocarbo] kenyoni, which was described by Siegel-Causey (1991) from the Aleutian Islands using midden remains and existing skeletal specimens. We emphasize a morphometric evaluation of the taxon using 224 skeletal specimens of North Pacific cormorants, but we also evaluate the qualitative characters originally used to characterize P. kenyoni. Principal components and discriminant function analyses of 14 skeletal characters failed to support the validity of the species. Similarly, all seven of the character states that Seigel-Causey described as unique to P. kenyoni also were found in P. pelagicus and P. urile. Thus, the three type specimens of P. kenyoni appear to be P. pelagicus. Although we could not confirm the validity of P. kenyoni, our morphometric analyses revealed that P. pelagicus individuals from the central Aleutians are smaller than those from surrounding populations.

Historically, a paucity of comparative morphological characters has led to much debate regarding relationships within and among the major lineages of New World nine-primaried oscines. More recently, DNA-DNA hybridization studies have provided novel and testable hypotheses of relationships, although no consensus has been reached. For 40 songbird taxa, we obtained 1,929 base pairs (bp) of DNA sequence from the mitochondrial cytochrome-b (894 bp) and NADH dehydrogenase subunit 2 (1,035 bp) genes. Phylogenetic analyses confirm the monophyly of this assemblage as traditionally defined. The lineages delineated historically on morphological grounds are retained; finches (Fringillinae) are sister to a well-supported clade (Emberizinae) containing blackbirds (Icterini), sparrows (Emberizini), wood-warblers (Parulini), tanagers (Thraupini), and cardinal-grosbeaks (Cardinalini). However, each tribe individually is either paraphyletic or polyphyletic with respect to most recent songbird classifications. Our results suggest that Euphonia is not a tanager but perhaps represents a derived form of cardueline finch. Piranga, traditionally considered a typical tanager, is a cardinaline in all of our analyses. Calcarius falls outside the sparrow lineage in all of our analyses, but its true affinities remain unclear. Elements of four different AOU families are represented in our clade Thraupini. The inclusion of several “tanager-finches” (Haplospiza, Diglossa, Tiaris, Volatinia, Sporophila) and a nectarivore (Coereba) in this clade is consistent with findings from other molecular phylogenies in suggesting that convergence in feeding specializations among some lineages has confounded traditional morphological classifications. We obtained a novel arrangement of relationships among tribes in our “best” topology; Cardinalini is sister to the rest of the Emberizinae assemblage (as defined by Sibley and Ahlquist [1990]), and Thraupini is sister to a clade containing Icterini, Emberizini, and Parulini. Despite nearly 2,000 bp of sequence for each taxon, and a high degree of stability across most weighting schemes and analytical methods, most nodes lack strong bootstrap support. The ND2 gene provided higher resolution than did cytochrome b, but combining genes provided the most highly supported and resolved topology. We consider the phylogeny a working hypothesis to be used as a guide for further studies within the nine-primaried oscine assemblage.

The Warbling Vireo (Vireo gilvus) is one of the most heavily parasitized host species of the Brown-headed Cowbird (Molothrus ater), suffering up to 80% parasitism in some areas. Warbling Vireo nests that are parasitized by cowbirds typically produce no vireo young. To make predictions about the consequences of brood parasitism on local host populations, we investigated factors that allow such high parasitism to occur. The major factors leading to high levels of brood parasitism on Warbling Vireos in the Okanagan Valley, British Columbia, are habitat overlap with cowbirds and the lack of response of vireos to cowbird eggs. Warbling Vireos responded more strongly to a cowbird dummy placed near the nest than to a dummy of a “neutral” species (junco) or to a common nest predator (crow). Preliminary simulation models based on population parameters obtained from three summers of fieldwork suggest that Warbling Vireos are in danger of extirpation from the Okanagan Valley if little movement of birds occurs between areas with different levels of brood parasitism. The models also indicate the sensitivity of this species to variation in adult and juvenile survival rates and number of successful broods produced per season. Our results emphasize the need for a metapopulation analysis that compares the population ecology of Warbling Vireos at high elevations (and probably with low parasitism) with that at low elevations (high parasitism) and that ascertains whether sufficient dispersal occurs between these populations to prevent extinction at lower elevations. Sufficient dispersal is indicated by apparently stable vireo populations in the Okanagan Valley and by Breeding Bird Survey data that show an overall increasing trend for this species in British Columbia.

We describe nest-site selection and report measures of breeding productivity from a population of Song Wrens (Cyphorhinus phaeocephalus) in central Panama. We studied 31 pairs from 1995 to 1998 and collected data on nest predation from 1996 to 1998. Song Wrens are year-round residents that build breeding nests for reproduction and dormitory nests for roosting. Twenty-five of 50 Song Wren breeding nests produced fledglings (daily nest survival rate = 0.968). Song Wrens usually (78%) placed their breeding nests in ant-defended acacias (Acacia melanoceras). However, nests placed in acacias did not experience lower rates of nest predation than nests placed in sites not defended by ants. The population-wide breeding season was seven months long, but individual pairs often bred within a span of only 2.5 months. Modal clutch size was two (n = 42), but the frequency of three-egg clutches was high (≥27%). Pairs that lost eggs or chicks renested more quickly than pairs that fledged young and attempted a second brood. Observed annual production of young was 1.4 fledglings per pair. Compared with other wrens, Song Wrens had a much longer breeding season and longer intervals between broods. The annual productivity of Song Wrens was the lowest recorded for any wren, which may have been due to smaller clutch sizes, long intervals between broods, and the correspondingly low number of nesting attempts per pair per year.

Using mitochondrial sequence data, we estimated phylogenetic relationships and genetic divergence among selected species of white-eyes (Zosteropidae). We focused on taxa endemic to islands in Micronesia, specifically Zosterops conspicillatus, Z. semperi, Z. hypolais, Rukia oleaginea, and Cleptornis marchei. We also included in our data set five additional species of Zosterops from the Indo-Australian region and three species from Africa, as well as additional passerine outgroups. Our mitochondrial sequence data revealed substantial genetic divergence (5.7 to 7.3%) among Z. conspicillatus, Z. semperi, and Z. hypolais, three taxa that formerly were treated as a single species. In addition, a sequence divergence of 6.5 ± SE of 1.7% was found between the population of Z. conspicillatus from Rota and “conspecific” populations on Guam, Tinian, and Saipan. The distinctiveness of the Rota population suggests that this taxon should be recognized as a distinct species, a result that bears on the conservation of this population because it has been declining dramatically in recent years. All optimal trees based on analysis of the mitochondrial sequence data place Rukia oleaginea within the genus Zosterops. In all optimal trees, Cleptornis marchei positions as the sister taxon to a clade including all other zosteropids included in this study. The trees based on our data strongly contradict the traditional classification of Cleptornis as a honeyeater (family Meliphagidae). Our data cannot resolve with any confidence the sister relationships of the insular endemic white-eyes, although the optimal trees suggest multiple colonizations of Micronesia by more than one white-eye lineage.

Fluctuating asymmetry (FA) may provide a direct test of whether sexual selection via “arbitrary traits” or “good genes” is responsible for the evolution of epigamic traits, because FA is an epigenetic measure of stress during development. However, tests of the FA hypothesis have yielded equivocal results, and the debate between arbitrary traits and good genes continues. The FA hypothesis predicts a negative relationship between ornament size and asymmetry. In non-ornamental traits, a U-shaped relationship between trait size and asymmetry is expected. We tested these predictions in the Red-collared Widowbird (Euplectes ardens) by examining the relationship between size and asymmetry in the length of the tail, tarsus, and wing. We found no significant linear or second-order polynomial relationships between trait size and asymmetry. Furthermore, no relationship existed between asymmetry and two indices of body condition. This suggests that the tail is not a reliable signal of male quality in the Red-collared Widowbird. However, we argue that the assumptions of the FA hypothesis are too simplistic for this conclusion to be drawn with a high degree of confidence.

We evaluated the relationship between blood parasites and body condition of American Kestrels (Falco sparverius) during the breeding season. Females that were infected with at least one species of parasite were in poorer condition than those without parasites during incubation but not prior to egg laying. We suggest that the relationship between parasitism and condition was masked before laying because of large increases in body mass of females during egg formation. Reduced condition of males during incubation also was associated with higher intensity of infections by Haemoproteus in one of two years. The negative association between condition and intensity of infection suggests that blood parasites impose costs on kestrels owing to competition for nutrients or allocation of energy by hosts to immune function or tissue repair. Alternatively, kestrels in poor condition may be more likely to have relapses of chronic infections, or they may be less able to control new infections because of resource limitations. In contrast to results during incubation, during the prelaying period the prevalence of parasites tended to be higher, and in one year infections were more intense, among males in good condition. One possible explanation for these results is that body condition of males during courtship is an important determinant of the quality of mate they are able to obtain, and males may be accumulating body reserves at the expense of decreased immune function. Return rates of female kestrels to the study area declined as the intensity of their Haemoproteus infections increased, suggesting that blood parasitism is associated with reduced survival or increased dispersal probability.

To address whether foraging strategies affect habitat-use patterns of nonbreeding warblers, I quantified foraging behavior, bill dimensions, and diet (based on regurgitation samples) of Ovenbirds (Seiurus aurocapillus) and Swainson's Warblers (Limnothlypis swainsonii) wintering in three habitats in Jamaica. Ovenbirds primarily gleaned prey from the surface of the leaf litter (95% of foraging maneuvers), resulting in a diet comprised predominantly of ants (62% of all prey items), seeds (18%), and beetles (9%). Swainson's Warblers foraged by lifting leaves (80% of foraging maneuvers), resulting in a significantly different diet dominated by beetles (39%), spiders (22%), and ants (19%). More than 60% of the regurgitation samples from Swainson's Warblers contained orthopterans and/or gecko (Sphaerodactylus goniorhynchus) bones. Averaged across all habitat types, Ovenbirds consumed ants in direct proportion to their abundance based on visual counts of arthropods. Swainson's Warblers consumed beetles more than expected based on the abundance of beetles in visual counts and Berlese funnels. The use of a diversity of habitats by Ovenbirds may be related to their ability to feed opportunistically on ants, which are a widespread, abundant, and reliable resource. In contrast, based on their foraging behavior and diet, Swainson's Warblers may be restricted to habitats with a well-developed canopy and an abundant subsurface leaf-litter fauna.

Although point counts are frequently used in ornithological studies, basic assumptions about detection probabilities often are untested. We apply a double-observer approach developed to estimate detection probabilities for aerial surveys (Cook and Jacobson 1979) to avian point counts. At each point count, a designated “primary” observer indicates to another (“secondary”) observer all birds detected. The secondary observer records all detections of the primary observer as well as any birds not detected by the primary observer. Observers alternate primary and secondary roles during the course of the survey. The approach permits estimation of observer-specific detection probabilities and bird abundance. We developed a set of models that incorporate different assumptions about sources of variation (e.g. observer, bird species) in detection probability. Seventeen field trials were conducted, and models were fit to the resulting data using program SURVIV. Single-observer point counts generally miss varying proportions of the birds actually present, and observer and bird species were found to be relevant sources of variation in detection probabilities. Overall detection probabilities (probability of being detected by at least one of the two observers) estimated using the double-observer approach were very high (>0.95), yielding precise estimates of avian abundance. We consider problems with the approach and recommend possible solutions, including restriction of the approach to fixed-radius counts to reduce the effect of variation in the effective radius of detection among various observers and to provide a basis for using spatial sampling to estimate bird abundance on large areas of interest. We believe that most questions meriting the effort required to carry out point counts also merit serious attempts to estimate detection probabilities associated with the counts. The double-observer approach is a method that can be used for this purpose.

Partitioning of nest heights among co-occurring species in response to nest predation has been proposed as a process that helps to structure avian species assemblages. In the experiment reported here, we used artificial nests baited with Japanese Quail (Coturnix japonica) eggs to test (1) whether both rate and final level of nest predation differed among nests placed at ground, shrub, and tree strata; and (2) whether vertical partitioning of nest sites among the three strata decreased nest predation. Although rates of nest predation increased from ground, to partitioned, to shrub, to tree strata, the only significant pairwise differences were between predation on ground nests versus all other treatments. The proportion of nests depredated at the conclusion of the experiment was lowest for the ground treatment, intermediate for the partitioned treatment, and highest for the shrub and tree treatments. Predation was significantly higher in 1988 than in 1989, and significant variation in predation occurred among five spatial replicates of the experimental treatments. Although the results show different susceptibilities to nest predation according to vegetative stratum, they show only a slight and nonsignificant reduction in nest predation as a consequence of vertical nest-site partitioning.

White-crowned Pigeons (Columba leucocephala) varied their timing of breeding and nesting intensity in response to variation in production of the four most important fruit species in their breeding-season diet in the upper Florida Keys. From 1988 through 1990, we monitored fruit production year-round in five habitats in which pigeons foraged and monitored all pigeon nests along two transects on Middle Butternut Key. Annually, pigeon breeding was positively correlated with summer rains and with the peak in overall fruit production. However, within the breeding season, only the availability of Metopium toxiferum was positively correlated with rainfall and the number of new clutches initiated. Both the timing and magnitude of breeding varied annually. In 1988, when Metopium was more available, more pigeons nested, the nesting season started earlier and lasted longer, and a large peak in nesting occurred when Metopium fruit ripened. During 1989 and 1990, when the relative availability of Metopium was lower, fewer pigeons nested, the nesting season was shorter, and the seasonal peak in nesting associated with Metopium fruit was reduced or absent. Nesting patterns did not appear to vary with changes in the relative availability of other fruits. White-crowned Pigeons appear to prefer Metopium fruits to other species. Because pigeons do not supplement nestling diets with arthropods, but augment their diets with protein-rich crop milk, they may depend on lipid-rich fruits such as Metopium to provide the energy for breeding and crop-milk production. Metopium fruit production may be influenced by rainfall and climatic conditions, both of which may vary spatially within the range of White-crowned Pigeons in Florida. Evidence that pigeons shift foraging sites when Metopium availability varies emphasizes the need to preserve large tracts of seasonal deciduous forest in the Keys and to protect Metopium trees in suburban areas where they are removed because they cause contact dermatitis in humans.

We studied hybridization and introgression between Black-capped (Poecile atricapillus) and Carolina (P. carolinensis) chickadees along two transects in the Appalachians using four genetic markers and multivariate analysis of morphology. Genetic data revealed that at least 58% of the birds in the center of each transect were of mixed ancestry and that recombinant genotypes predominated among hybrids, demonstrating that hybridization is frequent and that many hybrids are fertile. Genetic clines generally were steep and coincident in position, but introgression was evident well beyond the range interface. Introgression was higher at the one autosomal locus surveyed than in mitochondrial DNA or in two sex-linked markers, suggesting that the hybrid zone is a conduit for gene flow between the two forms at some loci. On a broad scale, morphometric variation was concordant with genetic variation. Clines in morphological variation based on principal components (PC) scores were steep and coincident with genetic clines. Also, a strong correlation within a population between PC scores and an individual's genetic makeup suggested that a large amount of morphological variation was genetically determined. However, morphological analysis indicated that hybrids were uncommon on one transect, whereas genetic data clearly showed that they were common on both. In addition, patterns of morphological variation were equivocal regarding introgression across the hybrid zone. Thus, genetic data provided a complementary and more detailed assessment of hybridization, largely due to the discrete nature of genetic variation. Genetic markers are useful in understanding hybridization and introgression, but diagnostic markers may underestimate average gene flow if selection against hybrids maintains steep clines at diagnostic loci. To gain a clearer picture of the genome-wide effects of hybridization, a much larger number of loci must be assayed, including non-diagnostic ones.

Area sensitivity in songbirds is commonly attributed to increased nest predation in forest fragments. In 1995 and 1996, we tested whether the nest predators and nesting success of an area-sensitive forest bird, the Eastern Yellow Robin (Eopsaltria australis), varied with fragment size, and we also conducted an artificial nest experiment. The study occurred in two small (55 ha) and two large (>400 ha) forest fragments in a matrix of agricultural land in New South Wales, Australia. Predation accounted for 95% of all failures of 282 robin nests, and the survival of robin nests was negatively correlated with how frequently we observed avian nest predators near nests (i.e. nest-predator activity). Of 461 artificial nests, 84% were depredated, nearly all (99%) by birds. Thus, birds were important predators of nests. The abundance, species richness, and activity of avian nest predators were not related to fragment size. Survival of robin nests averaged 19%; nests in small fragments had a 22% chance of producing at least one fledgling compared with 15% in large fragments, but the difference was not significant. Survival of artificial nests averaged 12% in both small and large fragments. Nest-predator activity accounted for the most variation (68%) in the fate of robin nests, followed by the cumulative density of open-cup nesters (16%). The placement of robin nests had no influence on nest fate. We conclude that nest predation was not area dependent and propose food supply as an alternative hypothesis to explain area sensitivity. We suggest that, rather than being related to fragment size, nest predation increases with decreasing forest cover in a landscape. Increased nest predation in fragmented compared with contiguous landscapes may lower the population viability of songbirds in a region, and hence regional numbers. Therefore, the spatial scale at which fragmentation influences nest predation and songbird populations must be considered carefully.

We used two different methods to estimate the density of nesting Peregrine Falcons (Falco peregrinus) across different parts of northern Eurasia. In the “territory-density” method, we extrapolated our density estimate of 406 km² per territory (95% CI = 295 to 650 km² per territory) in a high-density area, the Pyasina basin on the Taymyr Peninsula, to other similar areas across the range defined by published estimates. To estimate numbers in low-density areas, we used published data that suggested that Peregrine Falcon territories occur every 1,000 km². Based on the nesting association between Peregrine Falcons and Red-breasted Geese (Branta ruficollis), we used a second, post hoc method to provide a comparative estimate where the ranges of the two species overlap. This model was based primarily on the population ecology of the Red-breasted Goose and included parameters such as the proportion of the goose population nesting with peregrines, the proportion of peregrine pairs associated with geese, goose population size, and three other variables. Some of these variables were already known, whereas others had been estimated as part of another study. The territory-density and nesting-association methods led to estimates of 1,586 (95% CI = 991 to 2,179) and 2,417 (95% CI = 1,306 to 3,528) falcon territories, respectively, across the common range of Peregrine Falcons and Red-breasted Geese; the first method suggested a population of 3,652 falcon territories (95% CI = 2,282 to 5,018) across the entire range F. p. calidus. Although both approaches entailed several major assumptions, together they provide the only quantitative estimate of this remote population of Peregrine Falcons.

Male Club-winged Manakins (Machaeropterus deliciosus) are known to produce a unique mechanical sound with their extremely modified secondary feathers, yet the species remains poorly known behaviorally. I observed lekking males in Reserva Maquipucuna, Pichincha Province, Ecuador, to better understand the role of mechanical sounds, the behavioral repertoire, and other details of the natural history of this species. The behavioral repertoire of M. deliciosus is much more diverse than previously documented; it includes four mechanical phrases, two vocal sounds, and seven display behaviors. Mechanical sounds constitute the most prominent elements of the species' displays, replacing vocal sounds for territorial advertisement. I examine possible homology of the observed behaviors and propose a new phylogenetic hypothesis, that Machaeropterus forms a monophyletic clade with the genus Pipra, based on the existence of a complex shared courtship display.

An understanding of geographic and phylogenetic variation in passerine life histories is hampered by the scarcity of studies from the Southern Hemisphere. We documented the breeding biology of the White-browed Scrubwren (Sericornis frontalis), an Australia endemic in the Pardalotidae (parvorder Corvida). Like other members of the Pardalotidae, scrubwrens had a long laying interval (two days), a long incubation period (declining from 21 to 17 days through the season), and a long period of postfledging parental care (6 to 7 weeks). Scrubwrens appeared to be typical of the Australian Corvida in having a small clutch size (three eggs) and a long breeding season (5.4 months), and they also had a long interval between breeding attempts (10 days after a failed attempt, 21 days after a successful attempt). Scrubwrens were multibrooded, often raising two broods successfully and occasionally raising three broods. The breeding biology of scrubwrens adds further support to claims of a distinct life-history strategy for members of the Corvida but also reinforces evidence that some “Corvida” life-history traits more specifically are those of the Pardalotidae.