Registered users receive a variety of benefits including the ability to customize email alerts, create favorite journals list, and save searches.
Please note that a BioOne web account does not automatically grant access to full-text content. An institutional or society member subscription is required to view non-Open Access content.
Contact firstname.lastname@example.org with any questions.
Bicknell's Thrush (Catharus bicknelli) is a rare habitat specialist that breeds in dense balsam fir (Abies balsamea) and red spruce (Picea rubens) forests at high elevations in the northeastern United States. Ongoing and projected loss of this forest type has led to increased demand for information on the species' status throughout the region. We used elevation, latitude, and forest type to construct a model of Bicknell's Thrush distribution in New York, Vermont, New Hampshire, and Maine. The model predicts the species to be present in conifer-dominated forests above an elevation threshold that descends with increasing latitude. The slope of the threshold (−81.63 m/1° latitude) reflects climatic effects on forest composition and structure. The distribution model encompasses 136,250 ha of montane forest, including extensive areas of the White Mountains in New Hampshire and Adirondack Mountains in New York. To test model performance, we conducted point count and playback surveys along 1-km routes established in conifer forests above and below the threshold. The model accurately predicted the presence or presumed absence of Bicknell's Thrush on 61 of 72 routes (84.7%). When areas within 50 vertical m of the threshold were excluded, accuracy improved to 98.1%. The distribution model is a practical tool for conservation planning at local and regional levels. Potential applications include projecting effects of climate change on Bicknell's Thrush distribution, assessing risks of habitat alteration, and setting priorities for conservation and management.
We report an observation of Willow Ptarmigan (Lagopus lagopus) encountered 8 to 17 km from the nearest shoreline on Kuskokwim Bay, Alaska, on 30 August 2003. The ptarmigan were observed flying, landing on our research vessel, and landing and taking off from the water surface. We also report on one other observation of ptarmigan sitting on the water surface and other marine observations of ptarmigan from the North Pacific Pelagic Seabird Database. These observations provide evidence that Willow Ptarmigan are capable of dispersing across large bodies of water and landing and taking off from the water surface.
As human disturbance of natural landscapes increases, so does the need for information on declining, threatened, and potentially threatened native species. Proposed listing of the Mountain Plover (Charadrius montanus) as threatened under the U.S. Endangered Species Act in 1999 was found unwarranted in 2003, but this species remains of special concern to management agencies and conservation groups. Whereas large concentrations of breeding Mountain Plovers occur in Montana and Colorado, estimates of the numbers of Mountain Plovers in Wyoming have ranged from only 500 to 1,500 individuals and are based largely on conjecture. In 2002, we visited all known breeding locales in the state to define areas of concentrated sightings in the Laramie, Shirley, Washakie, Great Divide, and Big Horn basins. In 2003, we used distance sampling to estimate breeding bird densities in these five areas. We pooled these estimates and applied the resulting density to a minimum occupied range for the Mountain Plover based on the documented sightings and a previously derived home-range size of 56.6 ha ± 21.5 (SD) to generate a minimum population estimate for the state. Average Mountain Plover density was 4.47 ± 0.55 (SE) birds/km2. We calculated a minimum population estimate of 3,393 birds for Wyoming. The Mountain Plover population breeding in Wyoming appears to contribute substantially to a revised continental population estimate of 11,000 to 14,000 birds. Our approach may have applications to quantifying minimum population status of other uncommon species or species of special conservation concern using current database records, such as those compiled in Natural Heritage Programs at the state level.
Understanding the influences of habitat fragmentation on vertebrate populations is essential for the protection and ecological restoration of strategic sites for native species. We examined the effects of prairie fragmentation on avian reproductive success using artificial and natural nests on 26 randomly selected, privately owned patches of shortgrass prairie ranging in size from 7 to 454 ha within a cropland matrix in Washington County, Colorado, summer 2000. Survival trends of artificial and natural nests differed. Daily survival of artificial nests increased with patch size up to about 65 ha and differed little at larger patch sizes, whereas daily survival of Lark Bunting (Calamospiza melanocorys) and Horned Lark (Eremophila alpestris) nests decreased with increasing size of the grassland patch. We hypothesize that our unexpected findings of lower survival of natural nests with increasing patch sizes and different trends between artificial and natural nests are due to the particular structure of predator communities in our study area and the ways in which individual predators respond to artificial and natural nests. We recommend that the value of small habitat patches in highly fragmented landscapes not be overlooked.
Recent increases in the demand for communication towers have renewed interest in the impact of these towers on birds, particularly during migration. The objective of this study was to investigate avian mortality at two television towers (WGRZ and WKBW) in western New York from 1970 through 1999. Daily mortality totals ranged from 1 to 1,089 birds. The majority of the kill events were small, involving 10 or fewer birds; however, the majority of birds died in larger kill events. Both kill events and the numbers of individuals salvaged peaked in September. Patterns in avian mortality at the towers that we studied were consistent with normal migration events, during which the number of birds migrating varies substantially between nights. The two towers differed significantly in kill characteristics. At the WGRZ tower, median daily mortality generally ranged from 1 to 10 birds and was usually lower than at the WKBW tower. The size of kill events varied across the 3 decades, with no very large kill events (>500 birds) occurring in the 1990s. Because most birds salvaged in the 1970s and 1980s were killed in medium and large kill events, the absence of any very large kill events in the 1990s could explain the previously published decline in birds salvaged at these towers.
Current models to estimate daily energy expenditure (DEE) for free-living birds are limited to either those that use fixed thermoregulatory costs or those that more accurately estimate thermoregulatory costs, but require extensive and often logistically difficult measurements. Here, we propose a model based on basal metabolic rate (BMR), activity budgets, and site-specific energetic costs of thermoregulation that requires only simple measures of ambient temperature and wind speed to provide estimates of DEE. We use the model to calculate the DEE of Buffleheads (Bucephala albeola) wintering at six habitats that afford differing degrees of protection from exposure within Narragansett Bay, Rhode Island. Bufflehead activity budget data collected during the winters of 2001–2002 and 2002–2003, along with average temperatures and wind speeds at the sites, were used to calculate DEE that ranged from 46.9 to 52.4 kJ/hr and increased with increasing wind speed. The energetic cost of thermoregulation composed as much as 28% of total DEE and increased with wind speed. Our DEE values were 13.4% higher, and thermoregulatory costs were up to 2× higher than those calculated using an existing model that incorporates fixed thermoregulatory costs. We also saw an increase in feeding activity with increasing wind speed; sensitivity analysis of the effects of wind speed and feeding activity showed that a 1 m/sec increase in wind speed at our sites increased DEE by 2.5%, whereas a corresponding increase in feeding activity increased DEE by 4.5%. This suggests that in temperate winter habitats, increased feeding activity may have a greater impact on Bufflehead DEE than wind exposure. Site-specific model estimates of DEE could also provide additional insight into the relative contribution of environmental conditions and changes in waterfowl behavior to DEE.
We document the first cases of cattle behaving as avian predators, removing nestlings and eggs from three active ground nests in continuously grazed pastures in southwestern Wisconsin, 2000–2001. Cows removed three of four Savannah Sparrow (Passerculus sandwichensis) eggs from one nest (the fourth egg was damaged), all four Eastern Meadowlark (Sturnella magna) nestlings from another, and all three Savannah Sparrow nestlings from a third. We found only two of three missing eggs (intact) and one of seven missing nestlings (dead) near two of the nests. Cows may have eaten the egg and nestlings we were unable to account for; alternatively, the egg and nestlings may have been scavenged by predators or removed from the area by the adult birds. Without videotape documentation, we would have attributed nest failure to traditional predators and cattle would not have been implicated. We may be underestimating the impact of cattle on ground nests by not considering cattle as potential predators.
We used radio telemetry to examine Savannah Sparrow (Passerculus sandwichensis) home-range size and foraging and roosting behavior on Padre Island National Seashore in south Texas during January and February, 2002 and 2003. Savannah Sparrows maintained fixed home ranges in winter. Mean home-range size (95% Kernel Home Range [KHR]) was 9.1 ha with a mean core area (50% KHR) of 0.9 ha. Within home ranges, mean foraging and roosting areas were 5.6 and 6.6 ha, respectively. Three distinct habitat types were used by Savannah Sparrows on the island: foredunes (adjacent to the ocean), interior grasslands, and lagoons. Birds using the foredunes had significantly larger home ranges and traveled longer distances between their foraging and roosting locations, always moving inland to roost. Roosting and foraging areas overlapped less for these birds (20%) compared with the overlap for birds found in interior grasslands (45%) and lagoons (55%). The greater distance traveled to roost sites by birds foraging in the foredune habitat appeared to be related to increased exposure in that habitat type. Savannah Sparrows selected foraging areas with less vegetative biomass and more bare ground than random sites. Roost sites had greater total (live) cover than foraging and random sites. Savannah Sparrows foraged alone or in loose aggregations with conspecifics. Birds roosted alone or in aggregations of up to 30 individuals. Savannah Sparrows often roost outside of their foraging areas; this study draws attention to differences in space use for roosting and foraging Savannah Sparrows. Although Savannah Sparrows maintained relatively small home ranges, they occasionally moved at larger spatial scales, suggesting a need for intact grassland patches much larger than the average home-range size.
We studied the breeding ecology of the critically endangered Puaiohi (Myadestes palmeri), a poorly known Hawaiian thrush endemic to the island of Kauai. From 1996 through 1998, we monitored 96 active nests over the course of three breeding seasons. Mean clutch size was 2.0, and pairs produced an average of 1.5 fledglings/successful nest. Pairs renested after failure and some raised multiple broods. The mean annual reproductive effort was 2.1 nesting attempts/territory, and pairs produced a mean 1.1 fledglings/attempt. Large differences in nesting effort and productivity occurred among years, with mean number of fledglings/territory ranging from 0.4 to 4.9. Predation by owls (probably Short-eared Owls, Asio flammeus) and introduced rats (probably black rats, Rattus rattus) accounted for most nest failures. The presence of non-breeding floaters in the population and their largely unsuccessful attempts to gain territories in the study area suggest that the population is near carrying capacity. The high reproductive potential of the Puaiohi may help explain its persistence despite the species' historical rarity.
Little is known about Least Tern (Sterna antillarum) chicks from the time they leave the nest until fledging because they are highly mobile and cryptically colored. We evaluated the efficacy of using radio-telemetry to monitor Interior Least Tern (S. a. athalassos) chicks at Salt Plains National Wildlife Refuge, Oklahoma. In 1999, we attached radio transmitters to 26 Least Tern chicks and tracked them for 2–17 days. No adults abandoned their chicks after transmitters were attached. Transmitters did not appear to alter growth rates of transmittered chicks (P = 0.36) or prevent feather growth, although dermal irritation was observed on one chick. However, without frequent reattachment, transmitters generally did not remain on chicks <1 week old for more than 2 days because of feather growth and transmitter removal, presumably by adult terns. Although the presence of transmitters did not adversely affect Least Tern chicks, future assessments should investigate nonintrusive methods to improve retention of transmitters on young chicks and reduce the number of times that chicks need to be handled.
We sampled birds with mist nets and point counts in old-growth and second-growth Chaco forest in Argentina to compare the contribution of each method to estimates of species abundance and diversity. We captured 53 species with mist nets (13 exclusively), and detected 75 species on point counts (43 exclusively). Species richness estimated by rarefaction curves did not differ between methods, except in old-growth understory, where point counts detected fewer species than mist nets. Both methods showed similar patterns of bird diversity and distribution, although point counts revealed more differences between forest layers and forest types. Mist netting contributed to the detection of cryptic or secretive species, especially in the understory, but large-bodied (>200 g) species were detected by point counts alone. Multivariate analysis discerned guilds and species associated with different forest layers and types. Point counts seem to better reflect relative abundance, whereas mist nets may be more sensitive to bird activity (e.g., movements between resources). The simultaneous use of both techniques enhances the description of bird communities, and birds' use of habitats.
There are few published reports of Eastern Bluebirds (Sialia sialis) taking vertebrate prey or provisioning their young with vertebrates. We report finding a dead flat-headed snake (Tantilla gracilis) in an Eastern Bluebird nest. Flat-headed snakes feed primarily on soft-bodied invertebrates; thus, it is unlikely that the snake was attempting to depredate the bluebird nestlings. Moreover, flat-headed snakes are fossorial and rarely occur in open habitats. Therefore, the snake was most likely captured by one of the adult bluebirds and brought to the nestlings as a food item.
We document for the first time a Red-naped Sapsucker (Sphyrapicus nuchalis) usurping the nest of a Red-breasted Nuthatch (Sitta canadensis). A nuthatch nest in the incubation phase was usurped by a male Red-naped Sapsucker on 23 May 2003, and a sapsucker nest was initiated in the cavity on 1 June. Red-naped Sapsuckers are primary cavity excavators that normally nest in live and dead quaking aspens (Populus tremuloides) infected with heart rot fungus (Fomes spp.). Red-breasted Nuthatches are weak excavators that most commonly nest in broken-topped conifer snags. Nest usurpation was likely due to a shortage of suitable nest sites in our study plot.
The Wing-banded Antbird (Myrmornis torquata) is a poorly known suboscine passerine found in lowland Amazonian forests. Here, we present new information about the nest and nestlings of this enigmatic species. Our findings differ from previous observations and notes on clutch size.