Zimmerius villarejoi (Mishana Tyrannulet) is the second novel species to be described in recent years from poorly drained, white sand varillal forest near Iquitos, Depto. Loreto, Peru. It was initially detected by its vocalizations. Although well differentiated, close parallels in plumage and bill color suggest that Z. villarejoi may be most closely related to the poorly known and considerably larger Z. cinereicapillus (Red-billed Tyrannulet), with which it appears to be elevationally parapatric or allopatric. Amazonian forests growing on white sand and other nutrient poor soils hold many ornithological surprises and merit increased attention in field inventories.

The O‘ahu ‘Elepaio (Chasiempis sandwichensis ibidis) is a monarch flycatcher endemic to the Hawaiian island of O‘ahu. This forest bird has declined seriously in the last few decades and was listed as endangered under the federal Endangered Species Act in April 2000. The current distribution and population size of the O‘ahu ‘Elepaio are poorly known, and this information is vital to designing a recovery plan and implementing recovery actions. We surveyed most of O‘ahu for ‘Elepaio from 1992–2000 and compiled published and unpublished observations to estimate the current population size and construct current, recent historical, and prehistoric distribution maps. Based on 411 observations since 1991, we estimate the current population to be 1974 birds in six large subpopulations and several smaller ones. The breeding population consists of about 1768 birds due to a male-biased sex ratio, and the genetically effective population size is even lower because of the fragmented distribution. Total area of the current range is approximately 5486 ha, only 4% of the prehistoric range, and 25% of the range in 1975. Habitat loss to urbanization and agriculture caused large range reductions in the past, but cannot explain more recent declines. ‘Elepaio disappeared first from areas of higher rainfall, possibly because epizootics of introduced mosquito-borne diseases are more frequent where wetter conditions provide more mosquito breeding habitat. Management is urgently needed to prevent further declines and extirpation of smaller subpopulations.

The Cinnabar Hawk-Owl (Ninox ios) is a species recently described from a single specimen collected in 1985 from Bogani Nani Wartabone National Park in North Sulawesi, Indonesia. A second bird was trapped on 14 November 1999 in a mist net set in primary forest at 1420 m in Gunung Ambang Nature Reserve, North Sulawesi. Compared to the type specimen it had generally similar plumage and was larger. This second owl was captured on the boundary between an open area of marshland surrounded by hill forest dominated by pioneer species such as Macaranga hispida and Piper aduncum. Both trapped birds, and a recent sight record from Lore Lindu National Park in Central Sulawesi, suggest that N. ios is restricted primarily to high elevation forest on Sulawesi. Although the species is currently known from only three sites, the paucity of ornithological research on Sulawesi suggests N. ios may eventually prove to be more widespread.

Features of the nest cavity, nest tree, and surrounding vegetation have variously been shown to be important in nest site selection by cavity-nesting birds, yet few investigators have simultaneously considered these three habitat components. During 1995 and 1996 we considered each component in a study of nest site selection by Elf Owls (Micrathene whitneyi) in the Sonoran Desert. All Elf Owl nests (n = 68) were located in saguaros (Carnegiea gigantea) with a density of 0.032 nest saguaros/ha. At the scale of the nesting area, the number of cavities in a saguaro was the most important variable influencing whether it was selected for nesting; each additional cavity in a saguaro increased the odds it was selected by a factor of 4.4. Increasing the density of mature saguaros also increased the odds that an area was selected. At the scale of the nest saguaro, nest cavities were located in the main stem in greater proportion than their availability and were located higher above ground than random cavities. Nest cavities also were nonrandomly oriented toward the north, suggesting that cavity microclimate may influence nest site selection. Only 20–25% of potential nest cavities were occupied by cavity nesting birds, suggesting that habitat was not saturated. The differences between Elf Owl nest sites and potential nest sites at both the scale of the nesting area and nest saguaro suggest the presence of sufficient cavities to enable owls to occupy preferred sites within the study area.

We studied the use of regenerating clear cuts in the central highlands of New Brunswick by Bicknell's (Catharus bicknelli) and Swainson's (Catharus ustulatus) thrushes during the 1997 breeding season. Bicknell's Thrushes were found at 57 of the 90 points surveyed on six mountains. Swainson's Thrushes occupied 89 of 90 survey points. Bicknell's Thrushes had a lower probability of detection (P = 0.40) than Swainson's Thrushes (P = 0.76). Fixed-radius point counts yielded breeding density estimates for birds on individual mountains ranging from about 3–22 pairs/100 ha (average 16 pairs/100 ha) for Bicknell's Thrushes, and from about 39–69 pairs/100 ha (average 51 pairs/100 ha) for Swainson's Thrushes. White birch (Betula papyrifera), balsam fir (Abies balsamea), and pin cherry (Prunus pensylvanica) were the dominant tree species on regenerating sites. Points occupied by Bicknell's Thrushes tended to be at higher elevations than unoccupied points and to have a greater proportion of white birch stems, a greater number of stems in the 5–10 cm diameter class and a lower diversity of trees and shrubs. No attempt was made to characterize Swainson's Thrush habitat since this species was present at virtually all survey points. We believe that relatively young (average height about 4 m) mixed stands of regeneration with moderate to high stem densities provide important habitat for Bicknell's Thrushes in New Brunswick. Suggestions are made about the direction of future research needed to formulate habitat management and conservation plans for this species.

We examined shorebird use of mudflats, marsh islands, and nearby agricultural fields near Humboldt Bay in northwestern California between September 1988 and April 1989. Most species used fields for both foraging and roosting, including some species usually considered to be mudflat specialists. After seasonal rains began in late fall, Dunlins (Calidris alpina), Least Sandpipers (Calidris minutilla), Long-billed Curlews (Numenius americanus), and Marbled Godwits (Limosa fedoa) became opportunists and used fields at intermediate and high tides when mudflats were inundated. Black-bellied Plovers (Pluvialis squatarola) and Greater Yellowlegs (Tringa melanoleuca) were seasonal generalists during the two wettest seasons, using fields at all tides and mudflats at low and intermediate tides. Western Sandpipers (Calidris mauri) were mudflat specialists, and Willets (Catoptrophorus semipalmatus) were salt marsh opportunists that mainly used mudflats, but shifted to salt marsh at high tide. Killdeer (Charadrius vociferus) and Common Snipe (Gallinago gallinago) were field specialists and did not use the other two habitats in significant densities during any season. The presence of short vegetation and the presence or absence of standing water were the two most important characteristics influencing increased use of fields by all species.

Eight species of parids commonly occur in the mountains of northern Sichuan Province, People's Republic of China. They represent four monophyletic groups regarded by some authorities as genera, but more traditionally as subgenera of the large genus Parus. To test the competition-based hypothesis that less closely related species are more likely to co-occur, we used specimens and observations obtained in October 1989 and May 1991 to delineate the morphology, elevational range, and habitat associations of each species in this rich assemblage. A morphometric cluster analysis did not support the assumption that phylogenetic similarity predicts morphological and hence ecological similarity. Up to five species commonly co-occurred in mixed flocks, as in Europe (where five subgenera are represented), but a randomization test showed that community assembly was random with respect to subgenus. On the other hand, for the entire data set (P = 0.05) and during spring (P = 0.07), species in the same morphometric cluster were less likely to co-occur than were species with dissimilar morphology. It appears, therefore, that competition between species of similar morphology may play (or have played) some role in structuring assemblages of parids during the breeding season in this area. For this reason, more detailed studies of the parid assemblage in this area are recommended.

In a remote area of central Maine, I established bird feeders stocked with black oil sunflower seeds to supplement the food of wintering Black-capped Chickadees (Poecile atricapilla). The chickadees discovered experimental feeders established in late October within two weeks; feeders established in mid-January were discovered more slowly. Weekly censuses showed that chickadee abundance was significantly higher in the presence of the feeders. Mark-recapture analysis revealed that as many as 110 and 70 chickadees were using the feeders at the two most intensively studied sites over 2-day periods. Ambient temperature had no influence on the rate at which banded chickadees visited the feeders. The visitation rate of banded chickadees was higher during the first third of the winter; perhaps competition for feeder access increased as increasing numbers of unbanded chickadees used the feeders as the season progressed. The frequency of feeder use varied markedly among the chickadees at each feeding site; this variation could not be explained by age of the birds (first-winter versus adult birds). Variability in feeder use was also apparent for individual birds over time.

Columbids often exhibit irregular movement patterns in response to fruit abundance. We tested whether the abundance of nonbreeding Plain (Columba inornata) and White-crowned (C. leucocephala) pigeons was correlated with Thrinax parviflora fruit production in a dry forest in southeastern Jamaica. Monthly, from November to March, we counted the number of pigeons leaving the forest to roost in an adjacent mangrove swamp. Within two days of each roost count, we also counted all fruits on ten T. parviflora trees in the forest. Columbid and fruit counts showed similar patterns of temporal abundance, with increases from November to January and decreases from January to March. Peak (January) counts of White-crowned Pigeon, Plain Pigeon, and unidentified columbids were 129, 77, and 151, respectively. The peak Plain Pigeon count was approximately three times greater than the highest counts previously recorded for Jamaica. These data indicate that the Portland Ridge dry forest may provide a critical resource for the Plain Pigeon, perhaps at a time when fruit abundance is low on other parts of the island. Given the globally significant number of Plain Pigeons that use this site, protection from further development should be a priority.

We collected feces of breeding Harlequin Ducks (Histrionicus histrionicus) from interior rivers of Northern Québec, Labrador and Newfoundland to document their summer food habits. We obtained 42 samples from 50 ducks. All samples contained recognizable food items, and the mean number of taxa identified per sample was 3.6 (SD = 1.6, range = 1–7). Overall, a total of 10,222 organisms from 25 taxa were identified. Nearly all (99.7%) food items were insects; the rest were mollusks and mites. Among insects, Simuliidae larvae were the most common food item, representing 87.2% of all prey counted. Other insects had low relative frequencies, the highest being Trichoptera with only 8.0%. However, in terms of frequency of occurrence, many insects were well represented: Trichoptera (83.3%), Ephemeroptera (64.3%), Diptera (61.9%), Plecoptera (33.3%), Coleoptera (11.9%), and Heteroptera (9.5%). Although Simuliidae larvae may represent the most important food taken in terms of absolute numbers, the relative importance of Trichoptera may be much higher in terms dry weight. These results are consistent with observations that Harlequin Ducks usually feed on the bed of fast stretches of rivers, and occasionally in slow-moving waters.

During mating, and during the phases known as solitary male, harem formation, and harem, male Greater Rheas (Rhea americana) became vigilant to assure the elimination of competitors. High rates of harem defense and male expulsion were observed at the start, with levels decreasing gradually through the phases of mating, and male-male fighting mainly limited to the phase of harem formation. Courtship was nonexistent early in the mating period, reached a high level during the phases of harem formation and harem, then declined markedly just before harem breaking. The rates of all male social activities decreased significantly just before harem breaking.

We report nine new records of Brown-headed Cowbird (Molothrus ater) parasitism on the Common Grackle (Quiscalus quiscula): six from Benson County, North Dakota, and three from Delta Marsh, Manitoba. These observations represent 30% of the total number of records of parasitism on this host. Parasitism frequencies were 0.8% of 727 nests in North Dakota, and 4.0% of 75 nests in Manitoba. The data from Manitoba, combined with previous data from this location (Neudorf and Sealy 1994), yields a parasitism frequency of 3.4% of 119 nests examined. These parasitism frequencies are the highest recorded for the Common Grackle.

Calcium has been reported to be a limiting nutrient for eggshell production in birds living in areas of northern Europe suffering from heavy acid deposition. To investigate whether calcium might be limiting for birds in northeastern North America, a region also experiencing high and persistent acid precipitation, we analyzed eggshell characteristics and assessed calcium needs for eggshell production of a Neotropical migrant songbird, the Black-throated Blue Warbler (Dendroica caerulescens), in two forests in New England that differed in calcium content of their soils. We found no significant differences between the two regions in warbler eggshell mass, thickness, or in the concentration or the amount of calcium in eggshells. Moreover, calculations show that a diet of larval Lepidoptera, a major food source, is not a sufficient source of calcium for this species during egg laying, but that ingestion of eight average-sized (60 mg dry mass) snails during the egg-laying period would supply sufficient calcium for eggshell formation for a 4-egg clutch. Although current densities of snails suggest that they are not a limiting resource for birds at these sites, recent findings of declining calcium availability in New England forest soils suggest that calcium could in the future become a limiting factor for birds in northern temperate forests.

During a study of Red-cockaded Woodpecker (Picoides borealis) nesting in eastern Texas, we discovered a single breeding pair of woodpeckers with two simultaneous nests in nest trees that were 24 m apart. Incubation of eggs in each nest tree was at least 13 d and may have been as long as 16 d. The breeding male incubated and fed a nestling in one nest tree and the breeding female incubated and fed a nestling in the other nest tree until the nestlings were ≥24 d old. Prior to fledging, both the breeding male and female were observed feeding both nestlings in both nest trees. The pair successfully fledged the two nestlings, a single fledging from each nest tree, during one nesting cycle. After the nestlings were fledged, both the male and female woodpeckers were observed feeding both fledglings about 350 m from the pair of nest trees. Our observations indicate that there are exceptions to the current theory that the contribution by the breeding male and female to incubation and feeding of nestlings is essential and that neither the male nor the female can normally rear young birds without the contribution of the other.

I studied the breeding biology of the Crested Gallito (Rhinocrypta lanceolata) in the Reserve of Ñacuñán (western Argentina) from September 1995 to January 1999. The laying period extended from mid-September to late January, a month longer than previous reports from Argentina. The closed nest was globular with a side entrance and was made primarily of grasses. In Ñacuñán, this species preferred to nest in atamisque (Capparis atamisquea). Atamisques selected for nesting were 1.6–3.5 m in height, and nests were 1.0–2.1 m above the ground. Mean clutch size (2.2 eggs) did not show a year or a seasonal variation. Mean egg size and mass were less than those reported previously. The incubation period lasted 16–17 d and the nestling period 14–15 d. Eggs hatched asynchronously. No cases of brood parasitism by Shiny Cowbird (Molothrus bonariensis) were observed.

We observed an apparent incident of polygynous behavior in Giant Canada Geese (Branta canadensis maxima). Two females were paired with the same male and concurrently incubated side by side within the same nest tub. Reciprocal changes in the number of eggs within each bowl during incubation indicated that eggs were shifted between nest bowls in both years. This behavior was observed at the same location in two successive years. Goslings hatched from both nests each year. Polygynous behavior in typically monogamous Canada Geese has rarely been observed, and nest sharing has not been previously documented.

I observed the incubation and nestling periods of five nests of the Violet Sabrewing (Campylopterus hemileucurus) in Costa Rica. Each nest was built above running water. Mean incubation period was 20 d and only the female incubated. Mean nestling period lasted 23 d. Nestlings reached and surpassed adult mass before fledging (132% of adult size in males and 130% in females), although wing, tail, and culmen length did not reach adult size until after fledging. Because the Violet Sabrewing is highly sexually dimorphic in size and plumage color, I compared the postnatal development of five females and two males. Males were heavier than females and grew more slowly, consistent with generally slower growth rates in larger birds. The T_(10–90) period was 15.3 d for the fastest growing male and 13.8 d for the fastest growing female.

I report the intentional use of objects by American Crows (Corvus brachyrhynchos) in the contexts of foraging, nestling defense and play.

Kleptoparasitism has been extensively described for raptors and seabirds, but there are fewer observations for passerine birds. Here we describe several events of interspecific kleptoparasitism in the Great Kiskadee (Tyrannidae: Pitangus sulphuratus) in Buenos Aires, Argentina. Although interspecific kleptoparasitism has not been described previously for this species, we believe this foraging strategy is more common than expected for a passerine bird. The observations described in this paper are consistent with four of the six ecological conditions proposed by Brockmann and Barnard (1979).