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Availability of high-quality nest sites is thought to limit breeding populations of American Dippers (Cinclus mexicanus). To examine this hypothesis, we characterized dipper nest sites, nest-site habitat, and productivity in the central Oregon Coast Range. We also made additional nest sites (“created” nest sites = nest boxes, cliff ledges, hollowed logs that we constructed or created) along one of two creeks. Suitable nest sites (1) provided a physical space to place the nest, (2) were above the upper reach of flooding and inaccessible to ground predators, and (3) were very near to, or extended over, the stream's edge. Given these requirements, and within the context of swift, unpolluted mountain streams, dippers exhibited flexibility in their nest-site selection patterns and used a variety of nesting substrates. Streamside features associated with dipper nest sites included geomorphically constrained valleys (i.e., narrow valley floors), the presence of trees in the riparian zone (not tested statistically, but nearly universal to all nest sites), stream shading from overhead vegetation, and locations that were farther from areas frequented by humans (e.g., roads). Dippers readily used nesting substrates that we created, more than doubling the breeding population on a 10-km reach of stream (8 versus 3 nests/10-km reach). Reproductive success was high and not associated with any habitat feature we measured. The factors influencing recruitment in the Oregon Coast Range remain unknown.
We surveyed indigenous landbirds at two upland, mostly forested sites in southwestern Santo, Vanuatu. One site (Wunarohaehare, 600–1,250 m elevation) lies on the western, rain-shadowed slope of Mt. Tabwemasana. The other (Tsaraepae, 500–700 m elevation) is 16 km to the south, on the southeastern, very wet slope of Peak Santo. These are the richest single-site bird communities yet surveyed in Vanuatu, with 30 species of resident birds recorded at each site, 27 of which were common to both sites, including 6 species endemic to Vanuatu. We judged that 12 of the shared species were common at both sites. The non-overlapping species were a megapode, a parrot, and four understory passerines. We present new data on vocalizations for four species endemic to Vanuatu (Ptilinopus tannensis, Todiramphus farquhari, Neolalage banksiana) or to Vanuatu plus New Caledonia (Clytorhynchus pachycephaloides). We found less seasonality in breeding than previously reported for Vanuatu. Most human impact at the sites today may be from non-native mammals (rats, cats, pigs, cows), along with low levels of hunting and forest clearing. Based on prehistoric bones from elsewhere in Vanuatu, we suspect that formerly the sites on Santo may have supported additional species of megapode, hawk, parrot, and starling.
We provide the first descriptions of Micronesian Honeyeater (Myzomela rubratra saffordi) nests (n = 7) and nestlings (n = 6) from Saipan in the Mariana Islands. Measured nests (n = 3) averaged 46.7 mm in inner cup diameter, 65.7 mm in outer diameter, 41.3 mm in cup height, and 55.3 mm in external nest height. We found all nests in two species of native trees, 1.47–5.1 m above the ground. Nesting materials were primarily vine tendrils and Casuarina equisetifolia needles. We also report observations of parental behavior. Nests, nest placements, and behaviors appeared broadly similar to those reported for this species prior to its extirpation on Guam, and on other islands in Micronesia.
The Cerulean Warbler (Dendroica cerulea) is currently the focus of considerable management interest; however, our ability to develop effective management strategies is hampered by a dearth of life history and basic behavioral data. Here, we present information on male-female interactions of Cerulean Warblers and parental nest attentiveness that is, to our knowledge, among the first such rigorously collected data for this species. Males feed females during nest building and on the nest during incubation; the relative infrequency of these events suggests that they play more of a role in pair-bond maintenance than they do in enhancing female energetics. Female incubation rhythms were not significantly influenced by temperature, time of day, or egg age. Compared with other Dendroica warblers, we observed relatively infrequent female departures during incubation, perhaps in response to a high risk of nest predation. As the nestlings aged, females spent less time brooding nestlings, presumably to allow for more frequent feeding; however, both males and females exhibited relatively low rates of food delivery compared with other Dendroica warblers. Despite the low rates of food delivery, feeding trips were more frequent at successful nests than unsuccessful nests. Our results suggest that Cerulean Warblers are tightly constrained by the competing pressures of predation risk and sufficient food provisioning for nestlings.
White-throated Sparrows (Zonotrichia albicollis) display a plumage dimorphism (white-striped and tan-striped) with attendant behavioral differences, including greater aggression levels in white-striped birds and negative assortative mating, in which tan-striped birds pair with white-striped birds. To determine whether morph influences migration timing, which could influence patterns of assortative mating, we evaluated the phenology of northbound migration among White-throated Sparrows from a long-term banding dataset collected at a southern Ontario banding station. White-throated Sparrows are sexed by wing-chord length, but there is an intermediate size for which sex cannot be assigned. When all birds were considered together (both known and unknown sexes, n = 6,243), the white-striped birds migrated earlier by slightly more than 2 days. The sexing criteria, however, appeared to yield a sample that was not representative of the whole population: when we included only birds for which sex was assigned (n = 2,794, 45% of all birds), white-striped birds apparently migrated earlier by more than 4 days, but separate analyses of males (n = 1,511) and females (n = 1,283) revealed no differences in migration timing between morphs. By measuring wing-chord lengths of internally sexed specimens (from the Royal Ontario Museum) collected during April to June (n = 273), we found that in both sexes the wings of white-striped birds were about 2% longer than those of tan-striped birds. When we used these specimen data to recalibrate the sexing criteria, (a) it was possible to assign sex to 1.47 times as many birds (n = 4,121; 66% of all birds), (b) sex ratios of the banded birds more closely approached what appears to be the natural sex ratio (approximately 1:1), and (c) within-sex analyses indicated that white-striped females migrate earlier than tan-striped females by about 1.3 days, whereas there was no statistical difference between male morphs in migration timing.
Habitat degradation caused by feral grazers has been identified as a possible limiting factor for the endangered San Clemente Loggerhead Shrike (Lanius ludovicianus mearnsi). In 1999, we installed supplemental foraging perches within shrike breeding territories on San Clemente Island and observed shrike foraging behavior before and after perches were installed. Shrike foraging efficiency, determined by measuring foraging attack distances and success rates, was not improved when supplemental perches were present; however, shrikes shifted their focal foraging sites to areas where perches were installed. Shrike home ranges did not change size when supplemental perches were installed, indicating that foraging areas made available by adding supplemental perches were not of higher quality than those that were previously available. However, the addition of supplemental perches may have increased the total foraging habitat available to this endangered subspecies.
Although the majority of oscine species acquire a song repertoire by imitating songs they have been exposed to, some species also improvise and invent songs. To test the hypothesis that American Robins (Turdus migratorius) both imitate and invent the elements of their whistle songs, I analyzed the song repertoires of wild robins at three locations in western Massachusetts and the song development of five tutor-trained nestling robins. Robins appear to invent or improvise most of the elements in their repertoires (75–82%), but as fledglings and juveniles they acquire the remaining elements by imitating the songs of neighboring birds.
Throughout the United States, declines in breeding populations of grassland and shrubland birds have prompted conservation agencies and organizations to manage and restore early-successional habitats. These habitats support a variety of birds, some of which have been classified as generalists; thus, often these birds are thought to be less affected by habitat manipulation. More information, however, is needed on the response of early-successional generalists to habitat management, because conservation agencies are increasing their focus on the regional preservation and management of common species. On Nantucket Island, Massachusetts, the goal of the Partnership for Harrier Habitat Preservation (PHHP) has been to restore more than 373 ha of grassland for the island's population of Northern Harriers (Circus cyaneus). This management program has entailed methods such as prescribed burning and mowing (e.g., brushcutting) to restore and maintain grassland habitat. Over a 3-year period, we found that songbird response to burning and mowing varied among species, depending on subtle habitat preferences and the intensity and type of management. In shrublands, Eastern Towhee (Pipilo erythrophthalmus) and Common Yellowthroat (Geothlypis trichas) abundance declined in mowed areas but were unaffected by prescribed burning. In grasslands, Savannah Sparrow (Passerculus sandwichensis) abundance showed no response to either burning or mowing, whereas Song Sparrows (Melospiza melodia) preferred unmanaged grasslands. In shrublands, mowing was the most effective method for restoring grassland habitat, whereas prescribed burning had little effect on abundances of shrubland birds and vegetation structure. In grasslands, both mowing and burning were successful in restricting shrubland encroachment and maintaining grassland habitat.
We studied the movement patterns of European Robins (Erithacus rubecula) at stopovers during spring and fall migration on the southeastern Baltic Coast, Russia. On the 1st, and sometimes the 2nd, day after arrival at a stopover site, robin movements were less aggregated than those made on subsequent days. Search/settling time varied between several hours and 2 days. During this period, migrants either occupied a defined stopover area or left the site. Stopover duration was 1 to 12 days in spring (mean = 2.4 days ± 0.31 SE) and 1 to 14 days in fall (mean = 3.4 days ± 0.50). The home-range size of European Robins on the southeastern Baltic Coast did not differ between seasons (spring: 4,320 m2 ± 545, n = 15; fall: 3,562 m2 ± 598, n = 15) and was similar to that at a central European site in fall (4,264 m2 ± 241, n = 14). These home ranges were not defended territories. We found no relationship between the robins' spatial behavior and their fat stores on arrival, although in spring more lean than fat robins stopped for >2 days. The pattern of movements at the stopover was variable, both in birds that arrived lean and those that arrived with much more fat. Stopover duration estimates based on radio-tagging are superior to those based on capture-mark-recapture.
We compared timing and patterns of prebasic body molt between hatch-year (HY) and after-hatch-year (AHY) American Redstarts (Setophaga ruticilla) and Yellow Warblers (Dendroica petechia) in Ontario, Canada. In each body region of both species, there was no age-related difference in the proportion of individuals undergoing molt. Furthermore, there was no difference between HY and AHY American Redstarts in the overall timing of body molt; molt started in early July and lasted until early September. In contrast, HY Yellow Warblers started body molt in late June to early July, while adults began body molt in mid-July. Both American Redstarts and Yellow Warblers displayed age-class differences in the intensity and timing of molt among specific body regions. External factors (e.g., food availability and geographical distribution), and internal factors (e.g., physiological status) may contribute to variations in body molt timing observed in these two species.
We observed Bald Eagles (Haliaeetus leucocephalus) foraging at the landfill in Vancouver, British Columbia, Canada, 1994–1996 and 2001–2002, to determine (1) diet and time budgets of eagles visiting the landfill; (2) whether food taken from the landfill provided a significant energy source for local eagle populations; and (3) the effects of eagle density and weather on eagle behavior. Eagles fed primarily on human refuse (95%, n = 628), but food items taken from the landfill accounted for only 10 ± 3% of their daily energy needs. Subadults foraged at the landfill more often than adults, and most “refuse specialists” appeared to be subadults. Eagle time budgets consisted of mostly resting (91%), the remainder largely spent drinking (2.6%), scavenging (2.3%), and pirating (1.8%). Resting increased with wind speed, and foraging efficiency declined with precipitation, consistent with the hypothesis that the landfill is primarily a location for resting during inclement weather. Foraging efficiency decreased when number of eagles and piracies increased, and percent of eagles foraging decreased with increased numbers of eagles. The home ranges of only 2 of 11 radio-tagged eagles, both subadults, consisted largely (>20%) of the landfill; home-range size and percent of the home range that included the landfill were negatively correlated, suggesting that most eagles visited the landfill occasionally while a few spent most of their time there. We concluded that (1) the Vancouver landfill was not a major energy source for eagles, in part because their foraging is inefficient due to the large number of potential pirates; (2) most eagles apparently used the landfill primarily as a site for resting during inclement weather (the landfill is protected from the wind, is slightly warmer than surrounding areas due to decomposing refuse and the surrounding conifer trees, and is relatively free of human activity); and (3) a small population of largely subadult refuse specialists appeared to gain much or all of their energy from the landfill.
We examined territory selection of Red-winged Blackbirds (Agelaius phoeniceus) in experimental treatments with varied groundcovers and densities of planted and naturally occurring oaks (Quercus spp.) used by blackbirds for perching. We also compared vegetation parameters between blackbird territories and unused (i.e., unoccupied by Red-winged Blackbirds) areas. Although perch densities were greater in blackbird territories in unplanted controls and oak-planted treatments without redtop grass (Agrostis gigantea) than they were in unused areas, the low densities of perches in territories planted with redtop grass indicate that perch density is not limiting above some lower threshold. Territories, particularly in treatments with no redtop, tended to have greater mean grass cover and taller grass heights than unused areas. Our results are consistent with other studies in finding that Red-winged Blackbirds prefer areas having tall vegetation and dense grass.
Although loss of wetlands in southern Appalachia has been especially severe, no avian studies have been conducted in the vestiges of these ecosystems. Our research assessed avian use of southern Appalachian wetlands in the breeding seasons of 1999 through 2001. Site analyses included 18 habitat variables, including total wetland area, area of open water, beaver or livestock evidence, edge type (abrupt or gradual), and percent cover of nine vegetation types. We analyzed avian species richness and abundance at the community level and in guilds based on migratory status and breeding habitat preference. Measures of vegetation and habitat—particularly those resulting from beaver activities—and gradual edges were significantly correlated with guild- and community-level variables. Evidence of beaver (i.e., forest gaps where trees had been felled, ponds where drainages had been dammed; hereafter referred to simply as “beaver evidence”) was significantly correlated with greater community-level species richness and abundance. Both beaver evidence and gradual edge were positively associated with greater species richness and abundance of Neotropical migratory birds (NTMBs) overall, as well as with the late-successional NTMB guild. Presence of gradual edge alone also was significantly correlated with high abundance of birds in the early-successional NTMB guild. Beaver and gradual edge may have contributed to higher-quality breeding habitats with relatively greater overall productivity and structural complexity in some wetlands.
Although the breeding range of the Northern Saw-whet Owl (Aegolius acadicus) is restricted to North America, the northern limits of its range are still unclear. In Quebec, the most northerly confirmed breeding records had come from the Saguenay area (Chicoutimi; 48° 25′ N, 71° 03′ W) in balsam fir- (Abies balsamea) white birch (Betula papyrifera) forest and on the Gaspé Peninsula (Amqui; 48° 28′ N, 67° 25′ W) in balsam fir-yellow birch (B. alleghaniensis) forest. Between 1998 and 2003, however, we documented nine Northern Saw-whet Owl nests in balsam fir-black spruce (Picea marina) forest in boreal Quebec on the Mingan Terraces. These records extend the species' known breeding range northward to >50° N.
We report the first observation of a House Finch (Carpodacus mexicanus) successfully parasitizing a Carolina Wren (Thryothorus ludovicianus) nest. On 24 May 2005, we found a Carolina Wren nest in south-central Oklahoma containing four Carolina Wren eggs and two House Finch eggs. The House Finch eggs hatched and nestlings grew rapidly. The Carolina Wren eggs hatched but the young did not survive. We observed a House Finch fledgling with the adult Carolina Wrens the day after fledging.
American Coots (Fulica americana) are known for laying eggs in the nests of conspecifics, but there is little evidence that they regularly parasitize the nests of other species. I found 13 Least Bittern (Ixobrychus exilis) nests, 2 of which were parasitized by coots. These are the first records of coots parasitizing Least Bitterns, and the first records of any form of brood parasitism on Least Bitterns. Nests of Least Bitterns also were parasitized experimentally with a variety of nonmimetic eggs and 27% were rejected (n = 11 nests). This indicates that Least Bitterns may possess some egg recognition abilities.
On 5 June 2003, a female Brown-headed Cowbird (Molothrus ater) was found dead in a Carolina Chickadee (Poecile carolinensis) cavity nest near Bucyrus in Crawford County, Ohio. The cowbird had little room in the cavity and likely could not remove itself after laying an egg. Carolina Chickadee nests are rarely parasitized by brood parasites, and the size of their cavity entrances likely limits parasitism by Brown-headed Cowbirds. This is the first known instance of a Brown-headed Cowbird mortality after laying an egg in the cavity nest of a host species.
Great Black-backed Gulls (Larus marinus) are known to prey upon a wide range of bird species, particularly adults, young, and eggs of seabirds and waterfowl. Here, I provide the first account of Great Black-backed Gulls pursuing and attacking, in flight, a medium-sized wading bird, the Glossy Ibis (Plegadis falcinellus). I recorded two observations at Stratton Island, Maine, the northernmost breeding site for the Glossy Ibis in North America.
A tailless whipscorpion (Phrynus longipes) was observed feeding on an Antillean Crested Hummingbird (Orthorhyncus cristatus) atop a large boulder on the island of Virgin Gorda in the British Virgin Islands. This is the first record of any avian species serving as prey for an amblypygid.
I report on polydactyly in a Vaux's Swift (Chaetura vauxi). An extra, asymmetrically located toe was found on each foot of one swift. A check of 329 swifts from several museums produced no other examples of polydactyly in this species. A review of the literature and a query over the Internet, however, produced 10 other examples of polydactyly in wild birds.