The Gunnison Sage-Grouse (Centrocercus minimus) is described as a new species from southwestern Colorado and contrasted with the Sage-Grouse (Centrocercus urophasianus) from northern Colorado and western North America. Gunnison Sage-Grouse differ from all other described sage-grouse (C. u. urophasianus, C. u. phaios) in morphological measurements, plumage, courtship display, and genetics. The species currently is limited to 8 isolated populations in southwestern Colorado and adjacent San Juan County, Utah. Total estimated spring breeding population is fewer than 5000 individuals with the largest population (<3000) in the Gunnison Basin (Gunnison and Saguache counties), Colorado.

We discovered a Killdeer (Charadrius vociferus) incubating a nest containing three Mountain Plover (Charadrius montanus) eggs and three Killdeer eggs. The nest had been incubated about two weeks when discovered and was depredated three days later. To our knowledge this is the first known occurrence of a nest having eggs from both species.

We examined sexual size dimorphism of a lek-displaying diving duck from Australia, the Musk Duck (Biziura lobata). Like other lek-displaying species, Musk Ducks exhibit extreme sexual size dimorphism in addition to structural dimorphism. Body mass ratios (male:female) for Musk Ducks are among the highest reported for birds (more than 3:1). Multivariate analyses of 16 anatomical measurements indicated that body plans of male and female Musk Ducks have diverged isometrically except for the addition of a pendant lobe on lower mandibles of males. Within males, pendant lobe length, depth, and breadth were positively correlated with center rectrix length and bill width. Lobe area also was positively related to bill width, but not to center rectrix length. Lobe breadth and center rectrix length were positively related to overall body mass. Our results suggested that information about male physical quality may be conveyed to other Musk Ducks by parts of the anatomy most conspicuously exposed during sexual advertising displays. In contrast, anatomical features that function in foraging activity showed no sexual differences in anatomical shape relative to other parts of the anatomy that do not serve obvious foraging functions. We argue that foraging niche divergence or use of different food resources, if they have occurred, probably are secondary consequences of sexual size dimorphism.

We studied wintering Semipalmated Plovers (Charadrius semipalmatus) in a mangrove and open bay site in coastal Venezuela to determine whether the minor sexual dimorphism in bill and tarsus lengths in this species was correlated with sexual differences in habitat use, behavior during foraging, and diet. We found no significant differences between the sexes in either habitat use on the mudflats or distances to conspecifics. Neither sex exhibited territorial behavior. Males used significantly more shallow pecks than did females, who used more repetitive probing, particularly at the open bay site. Diets differed between the sexes in the relative abundance of prey in the fecal samples in both habitats, with samples from males containing significantly more dipteran larvae and samples from females containing more copepods and bivalves. Prey size did not vary between the sexes. We documented significant site differences in habitat use, foraging behavior, and diet, probably as a result of differences in prey availability.

We report the diet and the fate of seeds ingested by a family group of Salvin's Curassow (Mitu salvini) in Colombian Amazon. The study group consumed 123 plant species from 41 families. Of these, 106 species provided fruits, 21 seeds, 7 cotyledons, 19 flowers, and 9 leaves. Many species of invertebrates and vertebrates were also consumed. During the 14 months about 70% of the diet of each individual was composed of fruits. However, there was considerable temporal variation in diet composition and fruits were not always the most exploited item. Salvin's Curassow acts mainly as a seed predator (67% of the species eaten) on seeds longer than 5 mm but as a seed disperser (28% of the species eaten) for seeds shorter than 5 mm long, which were only rarely and opportunistically exploited. The remaining fruits eaten (5% of the species consumed) were neither dispersed nor predated. As a result of our study, we propose that Salvin's Curassows are mainly seed predators because most seeds ingested by the study group were preyed upon, and seed size was critical in determining seed fate.

The endangered Maui Parrotbill (Pseudonestor xanthophrys) is an excavating, insectivorous Hawaiian honeycreeper endemic to the high elevation rain forests of east Maui, Hawaii. From March 1994 to June 1997, we studied various aspects of their breeding ecology. We color-banded 18 individuals, located and monitored 9 active nests, and took behavioral data during 440 hrs of nest observation. Both members of a pair maintained a year-round, all-purpose territory that included nest sites and food resources. Maui Parrotbill were monogamous within and between years; we found no evidence of polyandry, polygyny, or helpers at the nest. Nests were cup-shaped, composed mainly of lichen interlaced with small twigs, and positioned in the outer canopy forks of mature ohia (Metrosideros polymorpha) trees. Modal clutch size was one. Females performed most nest construction and all incubation and brooding; males provisioned females and assisted in feeding nestlings after their fourth day. Fledglings depended on parental care for 5–8 months, during which their bill strength increased and foraging skills improved. We calculated the overall nest success rate by the Mayfield Method as 0.42 for the 1995/1996 and 1996/1997 breeding seasons combined. Nest failure and fledgling disappearance coincided with events of high rainfall. Their breeding ecology most closely resembled the Akiapolaau (Hemignathus munroi), another excavating, insectivorous Hawaiian honeycreeper found on Hawaii Island. As with the Akiapolaau, the threat of extinction is persistent and results from both the constraints of inherent life history traits and artificial ecological changes. We advocate the protection and expansion of habitable forest areas and an ongoing program to monitor and mitigate the effects of invasive species.

Striped Cuckoos (Tapera naevia) have three different song types. We investigated behavioral correlates of two using interactive playback to simulate territorial intrusion. Individuals sang one song type frequently when not interacting closely with neighbors, mates, or playback. A less common song type was sung by subjects that had approached playback closely, and by closely countersinging neighbors. These two song types distinguish different extents to which a singer may take initiative leading to interaction: the first provides information that the singer will probably stay put and not interact closely unless approached, the second that the singer will itself approach and search for another individual. Such distinctions are significant because they parallel recent results from diverse passerines, and because the information may be fundamental in enabling singers to obviate or elicit encounters with distant individuals.

Nest placement of open-nesting bird species may affect risk of nest predation, nest microclimate, and reproductive success. In populations that breed in multiple habitat types and over long seasons, nest placement should vary seasonally and by habitat to compensate for seasonally changing and habitat specific environmental conditions that might affect the relationship between nest placement and reproductive success. Using data collected during 1994 and 1995, I investigated seasonal and habitat specific patterns of nest placement in a population of California Gnatcatchers (Polioptila californica) that breeds over a 5 month period. Nest and substrate (plant in which nest is built) height increased and vegetative concealment of nests decreased seasonally, but these variables were not related to habitat type. Substrate height varied with substrate species in 1994, and use of individual substrate species varied seasonally. Reproductive phenology differed between the two major habitat types used by gnatcatchers in this study. Whether these seasonal and habitat specific changes in nest placement are adaptive responses to changing environmental conditions that may affect reproductive success has yet to be determined.

Accurate estimates of the amount of double-brooding within a population are an important parameter for assessing the population sustainability of forest birds. In 1998 and 1999, we color-banded adult female Wood Thrushes (Hylocichla mustelina) at 70 nests early in the breeding season to assess the frequency of double-brooding in a northern population. We found that double-brooding was a common breeding strategy among Wood Thrushes in southern Ontario. Forty-seven females fledged first broods and 74% (n = 35) of them initiated egg-laying in a subsequent nest. It is possible that at least 87% (n = 41) of the females were double-brooded, based on the evidence of 6 later nests built within 50 m of successful first nests that were depredated or fledged young before their owners could be identified. Other second-brood nests were probably missed because they were overlooked and because some females moved considerable distances (100–400 m) between nestings. Most birds that failed in their early nesting attempt were not found again on the site, precluding verification of their renesting efforts.

The effects of habitat and vegetation characteristics on the reproductive success of Yellow-breasted Chats (Icteria virens) were examined in central Kentucky. During the 1998 breeding season, 49 nests were located and monitored and the characteristics of nest sites and territories determined. Habitats where nests were located were categorized as old field, linear, or clump, and nests were classified as early or late. Chat nests were located in areas with more foliage and lateral cover than unused sites. However, most nests (55%) were not successful, and variables that differed between nest sites and random locations did not appear to influence nesting success. A diverse and, in an evolutionary sense, novel community of predators may eliminate predictably safe nest sites for chats on our study area. Chats in territories with more foliage cover and less canopy cover were more likely to fledge young. Dense foliage may lower the chances of nest predation by increasing the number of potential nest sites in a territory and may also provide better foraging habitat.

Wintering birds that use farm fields may benefit from strips of uncultivated, grassy, and weedy vegetation, called field borders. Field borders were established on 4 farms in the North Carolina coastal plain in Wilson and Hyde counties in the spring of 1996. In February of 1997 and 1998, bird numbers on field edges and field interiors, with and without field borders, were surveyed using strip transect and line transect methods. Most (93%) birds detected in field edges were sparrows, including Song (Melospiza melodia), Swamp (Melospiza georgiana), Field (Spizella pusilla), Chipping (Spizella passerina), White-throated (Zonotrichia albicollis), and Savannah (Passerculus sandwichensis) sparrows and Dark-eyed Juncos (Junco hyemalis). We detected more sparrows on farms with field borders than on farms with mowed edges. This difference was most pronounced in field edges where field borders contained 34.5 sparrows/ha and mowed edges contained 12.9 sparrows/ha. Sparrow abundance did not differ by treatment in field interiors. Sparrow density in field borders was intermediate to wintering sparrow densities reported in other studies. These results suggest that establishing field border systems may be an effective way to increase densities of overwintering sparrows on farms in the southeastern U.S. coastal plain.

Acadian Flycatcher (Empidonax virescens, n = 55), Indigo Bunting (Passerina cyanea, n = 60), Eastern Towhee (Pipilo erythrophthalmus, n = 41), and Wood Thrush (Hylocichla mustelina, n = 62) nests were monitored during 1995–1996 in the eastern panhandle of West Virginia, at the Sleepy Creek Wildlife Management Area. The objective of this study was to relate the outcomes of bird nests to surrounding habitat characteristics in an area that experienced heavy tree mortality from prior defoliation by the gypsy moth (Lymantria dispar). Large (> 22.9 cm dbh) standing snags in the nest patch were not associated with nest failure for any of the four bird species. Very large diameter (> 38.1 cm dbh) live trees and snags and reduced canopy cover increased the chances of Brown-headed Cowbird (Molothrus ater) parasitism only for Indigo Buntings. Nest patches of all four species differed in vegetation characteristics from random plots in similar habitat, typically by having greater densities of species' preferred nesting substrate in the nest patch. Gypsy moth defoliation, which can result in an increase in snags and opened canopy, is not likely to be a devastating ecological event for shrub and sub-canopy nesting avian species, and can create more nesting habitat for many species that use a dense forest understory.

Common Loon (Gavia immer) breeding, pre-migratory, and wintering behavior has been well described, but no previous author has characterized failed and non-breeding loon behavior during the summer breeding season. We quantified the summer behavior of non-breeding and failed breeding loons from 15 lakes in Kejimkujik National Park (Nova Scotia, Canada) and the Lepreau watershed (New Brunswick, Canada). Time-activity budgets and event quantifications were used to describe behavioral state and event patterns. The behavior of failed and non-breeders in summer is similar to that described for pre-nesting, pre-migratory, wintering, and breeding loons (except those with young chicks) with foraging the predominant behavior and peering the predominant event. We propose that the behavioral regimen of adult loons is relatively constant throughout the year, with the exception of a two-week period following chick hatching when adults brood their young.

Prey remains of a nestling Harpy Eagle (Harpia harpyja) over 15 months in eastern Amazon, Brazil included 11 two-toed sloths (Choloepus didactylus), 9 three-toed sloths (Bradypus variegatus), and 1 gray four-eyed opossum (Philander opossum). We found no evidence of predation on primates despite their abundance in the area and their importance to Harpy Eagles studied elsewhere. We observed no sloths in 605 km of line transects, a finding that suggests the inadequacy of transect data to estimate prey density for Harpy Eagles.

Northern Goshawks (Accipiter gentiles) nesting in south central Wyoming consumed at least 33 species of prey; 14 were mammals and 19 were birds. Based on percent occurrence in regurgitated pellets, dominant (>10% frequency) prey species included: red squirrel (Tamiasciurus hudsonicus; present in 50% of pellets), Northern Flicker (Colaptes auratus; 34%), American Robin (Turdus migratorius; 30%), golden-mantled ground squirrel (Spermophilus lateralis; 27%), and Uinta or least chipmunk (Tamias spp.; 10%). Woodpeckers [combined frequency of occurrence for Northern Flicker, Red-naped Sapsucker (Sphyrapicus nuchalis), Hairy Woodpecker (Picoides villosus), Three-toed Woodpecker (Picoides tridactylus), and unknown species] were present in 52% of pellets. Unusual food items in the diet included mule deer (Odocoileus hemionus) and American marten (Martes americana).

Several bird species are thought to be itinerant breeders, reproducing in different localities during the same season, but this behavior has been documented conclusively only in the Red-billed Quelea (Quelea quelea). In 1997, I observed a case of itinerant breeding and mate switching by a banded female American Dipper (Cinclus mexicanus) in western Montana. This female raised a successful first brood on a bridge early in the breeding season, then moved 5 km to a neighboring drainage and successfully raised a second brood in a crevice with a different male. This reproductive behavior may have been facilitated in my study area by the use of low-elevation bridges as nest sites by dippers.

Four eggs in a Yellowhammer (Emberiza citrinella) nest were incubated for one day by a female Yellowhammer but subsequently abandoned. The day following abandonment, the nest and the clutch were adopted by a female Blackcap (Sylvia atricapilla) who incubated the eggs until a single Yellowhammer nestling hatched; two eggs were depredated, and the embryo in the third egg was dead but well-developed. The young Yellowhammer was fed for 6 days until it was taken by a predator. Because there were no obvious benefits for the adopting female Blackcap, we speculate that the adoption resulted from misdirected parental behavior.

Populations of Golden-winged Warblers (Vermivora chrysoptera) and Blue-winged Warblers (V. pinus) have coexisted in the Hudson Highlands for a century. Previous researchers in our study area suggested this unusual coexistence might be due to a low frequency of hybrids. However, during the 1998–1999 breeding season we found that 10% of the males were hybrids, a value similar to many studies elsewhere. We observed that hybrid males ceased singing and other conspicuous behaviors early in the breeding season. Pair formation and nesting by hybrids appeared to be rare, perhaps because of the reduced vigor of their displays. Most of the fieldwork by previous researchers in this area was conducted after the date when hybrids cease singing, which may account for prior reports of the absence of hybrids.

We recorded examples of complex, highly variable, song-like vocalizations uttered by female Chestnut-sided Warblers (Dendroica pensylvanica) in Massachusetts and New Hampshire. These songs occurred only during a brief period just after females arrived on the breeding grounds and were almost invariably associated with intense social interactions. Although the timing and context of the songs might suggest a territorial defense or other communicative function, the songs bore no resemblance to male songs, were uttered infrequently, and were used by only a small proportion of females. Therefore, we believe it is unlikely that the songs could be reliably recognized and interpreted by conspecifics. Perhaps the vocalizations are byproducts of seasonally high levels of circulating sex hormones, as suggested by the prolonged singing that we observed in a captive-reared female that had been implanted with testosterone.

A pair of Black-vented Orioles (Icterus wagleri) successfully fledged young from a nest inside a log cabin in the Montecristo National Park, El Salvador. This is the first breeding record of the species for El Salvador. The nest was hammock-shaped, 18 × 20 cm outside, 6 cm deep inside, and contained four eggs. After the first clutch failed, the pair renested using the same nest, incubating and rearing three young over 34 days.

On 16 June 1999, I found a Lesser Scaup (Aythya affinis) nest parasitized by a Brown-headed Cowbird (Molothrus ater). On 22 June the female scaup had begun incubating the 10 scaup eggs but the cowbird egg was missing, presumably ejected by the female scaup.

In 1993 and 1994, we collected data on the diet and foraging behavior of Roadside Hawks (Buteo magnirostris) in primary tropical forest with slash-and-burn farming landscape nearby. We identified 140 prey items brought to nests: 90 in the farming landscape and 50 in the forest. Reptiles (57.1%, mostly lizards) and amphibians (24.3%) were the main prey types delivered to nestlings in both habitats, but size and type of prey differed between nests in the two habitats. Relatively more amphibians and reptiles were delivered to slash-and-burn nests and more mammals and insects to forest nests. In 40 of 44 prey capture attempts, Roadside Hawks utilized the typical Buteo technique, searching for prey from a perch and attacking once prey was sighted. In addition, two aerial attacks were directed at a flying and at a perched bird, and hawks walking on the ground twice captured beetles. Of 44 capture attempts, 84% were successful. In the forest, half of 32 attacks were launched from perches protruding above vegetation along a road or in clearings; the other half were launched from perches beneath the forest canopy. These hawks often took advantage of special hunting opportunities: attending army-ant swarms, taking many frogs immediately after rain showers, and catching prey fleeing from fires.

The Stripe-tailed Hummingbird (Eupherusa eximia) prefers nectar that is highly supplemented in both vitamins and minerals, when offered the choice of no, low, or high supplemented nectar. We tested the responses of hummingbirds in southern Brazil to four solutions: nectar, nectar supplemented with vitamins, nectar supplemented with minerals, and water with both vitamins and minerals added. Hummingbirds spent less time at and made fewer visits to the supplemented water than to the different nectar solutions, suggesting that nutrients alone are not enough to attract birds. One of eight species, the Violet-capped Woodnymph (Thalurania glaucopis), visited the mineral supplemented nectar more often than both nectars and one unidentified hermit species (Phaethornis sp.) visited the mineral treatment more than straight nectar. The Black-throated Mango (Anthracothorax nigricollis) made more visits to the vitamin supplemented nectar than to mineral-rich nectar whereas the Glittering-bellied Emerald (Chlorostilbon aureoventris) avoided the vitamin treatment, preferring straight nectar. A general pattern of preference was not found among species.

We report the first records of the ingestion of a toxic California newt (Taricha torosa) and a particular species of Jerusalem cricket (Stenopelmatus fuscus) by a Great Horned Owl (Bubo virginianus). This is one of only a few records of avian predation on this genus of toxic newt. Ingestion of the extremely poisonous tetrodotoxin present in the newt's skin was likely the cause of the owl's death.