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At least 199 records · Page 11Linked to original sources
USGS2010

Isotopic characterization of flight feathers in two pelagic seabirds: Sampling strategies for ecological studies

We wish to use stable-isotope analysis of flight feathers to understand the feeding behavior of pelagic seabirds, such as the Hawaiian Petrel ( Pterodroma sandwichensis ) and Newell’s Shearwater ( Puffinus auricularis newelli ). Analysis of remiges is particularly informative because the sequence and timing of remex molt are often known. The initial step, reported here, is to obtain accurate isotope values from whole remiges by means of a minimally invasive protocol appropriate for live birds or museum specimens. The high variability observed in D 13 C and D 15 N values within a feather precludes the use of a small section of vane. We found the average range within 42 Hawaiian Petrel remiges to be 1.3‰ for both D 13 C and D 15 N and that within 10 Newell’s Shearwater remiges to be 1.3‰ and 0.7‰ for D 13 C and D 15 N, respectively. The D 13 C of all 52 feathers increased from tip to base, and the majority of Hawaiian Petrel feathers showed an analogous trend in D 15 N. Although the average range of DD in 21 Hawaiian Petrel remiges was 11‰, we found no longitudinal trend. We discuss influences of trophic level, foraging location, metabolism, and pigmentation on isotope values and compare three methods of obtaining isotope averages of whole feathers. Our novel barb-sampling protocol requires only 1.0 mg of feather and minimal preparation time. Because it leaves the feather nearly intact, this protocol will likely facilitate obtaining isotope values from remiges of live birds and museum specimens. As a consequence, it will help expand the understanding of historical trends in foraging behavior

Hawaii↗
USGS2010

Seasonal movements, winter range use, and migratory connectivity of the Black Oystercatcher

The Black Oystercatcher (Haematopus bachmani) is an intertidal obligate along North America's Pacific coast and a species of high conservation concern (population size 8900-11 000 individuals). Understanding birds' movements and space use throughout the annual cycle has become paramount in the face of changing environmental conditions, and intertidal species may be particularly vulnerable to habitat change due to anticipated sea-level rise associated with climate change and increasing coastal development. Conservation of the Black Oystercatcher is hindered by a lack of information on the species' nonbreeding distribution, seasonal movements, and habitat connectivity. Using satellite (n = 19) and VHF (n = 19) radio transmitters, we tracked Black Oystercatchers from five breeding sites (Vancouver Island, British Columbia; Kodiak Island, Prince William Sound, Middleton Island, and Juneau, Alaska) through one and one half annual cycles (May 2007-Dec 2008). We documented medium- to long-distance migration (range of migration distance 130-1667 km) in three populations (Prince William Sound, Middleton Island, and Juneau) and year-round residency in two others (Kodiak and Vancouver Island). We observed variation in the timing and length of migration by study site, and individual birds demonstrated fidelity to breeding and nonbreeding sites. We did not observe strong migratory connectivity. Migratory oystercatchers distributed themselves widely along the coasts of British Columbia and southeast Alaska during winter. Results provide baseline information on the Black Oystercatcher's movements and space use throughout the annual cycle. ?? 2010 The Cooper Ornithological Society.

Condor↗
USGS2010

Parental investment decisions in response to ambient nest-predation risk versus actual predation on the prior nest

Theory predicts that parents should invest less in dependent offspring with lower reproductive value, such as those with a high risk of predation. Moreover, high predation risk can favor reduced parental activity when such activity attracts nest predators. Yet, the ability of parents to assess ambient nest-predation risk and respond adaptively remains unclear, especially where nest-predator assemblages are diverse and potentially difficult to assess. We tested whether variation in parental investment by a multi-brooded songbird (Brewer's Sparrow, Spizella breweri) in an environment (sagebrush steppe) with diverse predators was predicted by ambient nest-predation risk or direct experience with nest predation. Variation among eight sites in ambient nest-predation risk, assayed by daily probabilities of nest predation, was largely uncorrelated across four years. In this system risk may therefore be unpredictable, and aspects of parental investment (clutch size, egg mass, incubation rhythms, nestling-feeding rates) were not related to ambient risk. Moreover, investment at first nests that were successful did not differ from that at nests that were depredated, suggesting parents could not assess and respond to territorylevel nest-predation risk. However, parents whose nests were depredated reduced clutch sizes and activity at nests attempted later in the season by increasing the length of incubation shifts (on-bouts) and recesses (off-bouts) and decreasing trips to feed nestlings. In this unpredictable environment parent birds may therefore lack sufficient cues of ambient risk on which to base their investment decisions and instead rely on direct experience with nest predation to inform at least some of their decisions. ?? 2010 The Cooper Ornithological Society.

Condor↗
USGS2010

Foraging proficiency during the nonbreeding season of a specialized forager: are juvenile American Oystercatchers "bumble-beaks" compared to adults?

In many species, immature individuals are less proficient at foraging than are adults, and this difference may be especially critical during winter when survival can be at its minimum. We investigated the foraging proficiency of adult and immature American Oystercatchers ( Haematopus palliatus ) during the nonbreeding season. Oystercatchers forage on prey that must be handled with specialized skills, so age-related differences in foraging behavior may be expected. We found that adults spent more time searching than did immatures, a trend toward immatures taking longer to handle prey than did adults, and immatures more often handling prey unsuccessfully than did adults. Feeding rates and diet composition did not differ by age class. We posit that the immature birds traded off longer handling times with shorter searching times and that ultimately the abundant prey in the region may contribute to the ability of immature birds to feed at rates similar to those of adults.

Condor↗
USGS2011

A puzzling migratory detour : Are fueling conditions in Alaska driving the movement of juvenile sharp -tailed sandpipers ?

Making a detour can be advantageous to a migrating bird if fuel-deposition rates at stopover sites along the detour are considerably higher than at stopover sites along a more direct route. One example of an extensive migratory detour is that of the Sharp-tailed Sandpiper ( Calidris acuminata ), of which large numbers of juveniles are found during fall migration in western Alaska. These birds take a detour of 1500–3400 km from the most direct route between their natal range in northeastern Siberia and nonbreeding areas in Australia. We studied the autumnal fueling rates and fuel loads of 357 Sharp-tailed Sandpipers captured in western Alaska. In early September the birds increased in mass at a rate of only 0.5% of lean body mass day -1 . Later in September, the rate of mass increase was about 6% of lean body mass day -1 , among the highest values found among similar-sized shorebirds around the world. Some individuals more than doubled their body mass because of fuel deposition, allowing nonstop flight of between 7100 and 9800 km, presumably including a trans-oceanic flight to the southern hemisphere. Our observations indicated that predator attacks were rare in our study area, adding another potential benefit of the detour. We conclude that the most likely reason for the Alaskan detour is that it allows juvenile Sharp-tailed Sandpipers to put on large fuel stores at exceptionally high rates.

Alaska↗
USGS2011

Winter distribution of willow flycatcher subspecies

Documenting how different regions across a species' breeding and nonbreeding range are linked via migratory movements is the first step in understanding how events in one region can influence events in others and is critical to identifying conservation threats throughout a migratory animal's annual cycle. We combined two studies that evaluated migratory connectivity in the Willow Flycatcher ( Empidonax traillii ), one using mitochondrial DNA sequences from 172 flycatchers sampled throughout their winter range, and another which examined morphological characteristics of 68 museum specimens collected in the winter range. Our results indicate that the four subspecies occupy distinct but overlapping regions of the winter range. Connectivity between specific breeding and winter grounds appears to be moderate to strong, with distributions that suggest migration patterns of both the chain and leap-frog types connecting the breeding and nonbreeding grounds. The Pacific lowlands of Costa Rica appear to be a key winter location for the endangered Southwestern Willow Flycatcher ( E. t. extimus ), although other countries in Central America may also be important for the subspecies.

The Condor↗
USGS2011

Latitudinal variation in reproductive strategies by the migratory Louisiana Waterthrush

We evaluated hypotheses that seek to explain breeding strategies of the Louisiana Waterthrush (Parkesia motacilla) that vary across a latitudinal gradient. On the basis of data from 418 nests of color-banded individuals in southwestern Pennsylvania and 700 km south in the Georgia Piedmont, we found that clutch size in replacement nests and probability of renesting were significantly greater in Pennsylvania (clutch size 4.4; renesting probability 0.66) than in Georgia (clutch size 3.8; renesting probability 0.54). Contrasts of the remaining measures of breeding were not statistically significant, and, in particular, mean daily nest survival in the two study areas was nearly identical (0.974 in Pennsylvania; 0.975 in Georgia). An individual-based model of fecundity (i.e., number of fledged young per adult female), predicted that approximately half of the females in both Pennsylvania and Georgia fledge at least one young, and mean values for fecundity in Pennsylvania and Georgia were 2.28 and 1.91, respectively. On the basis of greater support for the food-limitation hypothesis than for the season-length hypothesis, the trade-off between breeding in a region with more food but making a longer migration may be greater for waterthrushes breeding farther north than for those breeding farther south. ?? The Cooper Ornithological Society 2011.

Condor↗
USGS2011

Tamarisk biocontrol using tamarisk beetles: Potential consequences for riparian birds in the southwestern United States

The tamarisk beetle ( Diorhabda spp.), a non-native biocontrol agent, has been introduced to eradicate tamarisk ( Tamarix spp.), a genus of non-native tree that has become a dominant component of riparian woodlands in the southwestern United States. Tamarisk beetles have the potential to spread widely and defoliate large expanses of tamarisk habitat, but the effects of such a widespread loss of riparian vegetation on birds remains unknown. We reviewed literature on the effects of other defoliating insects on birds to investigate the potential for tamarisk beetles to affect birds positively or negatively by changing food abundance and vegetation structure. We then combined data on the temporal patterns of tamarisk defoliation by beetles with nest productivity of a well-studied riparian obligate, the Southwestern Willow Flycatcher ( Empidonax traillii extimus ), to simulate the potential demographic consequences of beetle defoliation on breeding riparian birds in both the short and long term. Our results highlight that the effects of tamarisk biocontrol on birds will likely vary by species and population, depending upon its sensitivity to seasonal defoliation by beetles and net loss of riparian habitat due to tamarisk mortality. Species with restricted distributions that include areas dominated by tamarisk may be negatively affected both in the short and long term. The rate of regeneration and/or restoration of native cottonwoods ( Populus spp.) and willows ( Salix spp.) relative to the rate of tamarisk loss will be critical in determining the long-term effect of this large-scale ecological experiment.

Arizona, Colorado, New Mexico, Utah↗
USGS2011

Migration patterns, use of stopover areas, and austral summer movements of Swainson's hawks

From 1995 to 1998, we tracked movements of adult Swainson's Hawks ( Buteo swainsoni ), using satellite telemetry to characterize migration, important stopover areas, and movements in the austral summer. We tagged 46 hawks from July to September on their nesting grounds in seven U.S. states and two Canadian provinces. Swainson's Hawks followed three basic routes south on a broad front, converged along the east coast of central Mexico, and followed a concentrated corridor to a communal area in central Argentina for the austral summer. North of 20° N, southward and northward tracks differed little for individuals from east of the continental divide but differed greatly (up to 1700 km) for individuals from west of the continental divide. Hawks left the breeding grounds mid-August to mid-October; departure dates did not differ by location, year, or sex. Southbound migration lasted 42 to 98 days, northbound migration 51 to 82 days. Southbound, 36% of the Swainson's Hawks departed the nesting grounds nearly 3 weeks earlier than the other radio-marked hawks and made stopovers 9.0–26.0 days long in seven separate areas, mainly in the southern Great Plains, southern Arizona and New Mexico, and north-central Mexico. The birds stayed in their nonbreeding range for 76 to 128 days. All used a core area in central Argentina within 23% of the 738 800-km 2 austral summer range, where they frequently moved long distances (up to 1600 km). Conservation of Swainson's Hawks must be an international effort that considers habitats used during nesting and non-nesting seasons, including migration stopovers.

The Condor↗
USGS2011

Intercontinental gene flow among western arctic populations of Lesser Snow Geese

Quantifying the spatial genetic structure of highly vagile species of birds is important in predicting their degree of population demographic and genetic independence during changing environmental conditions, and in assessing their abundance and distribution. In the western Arctic, Lesser Snow Geese ( Chen caerulescens caerulescens ) provide an example useful for evaluating spatial population genetic structure and the relative contribution of male and female philopatry to breeding and wintering locales. We analyzed biparentally inherited microsatellite loci and maternally inherited mtDNA sequences from geese breeding at Wrangel Island (Russia) and Banks Island (Canada) to estimate gene flow among populations whose geographic overlap during breeding and winter differ. Significant differences in the frequencies of mtDNA haplotypes contrast with the homogeneity of allele frequencies for microsatellite loci. Coalescence simulations revealed high variability and asymmetry between males and females in rates and direction of gene flow between populations. Our results highlight the importance of wintering areas to demographic independence and spatial genetic structure of these populations. Male-mediated gene flow among the populations on northern Wrangel Island, southern Wrangel Island, and Banks Island has been substantial. A high rate of female-mediated gene flow from southern Wrangel Island to Banks Island suggests that population exchange can be achieved when populations winter in a common area. Conversely, when birds from different breeding populations do not share a common wintering area, the probability of population exchange is likely to be dramatically reduced.

The Condor↗
USGS2011

Vagrant western red-shouldered hawks: origins, natal dispersal patterns, and survival

We report the results of a 40-year study of the western Red-shouldered Hawk (Buteo lineatus elegans) involving the banding of 2742 nestlings in southern California from 1970 to 2009 (this study) plus 127 nestlings banded in other California studies (1956–2008) and the analyses of 119 records of subsequent recovery from the Bird Banding Laboratory (1957–2009). Of the Red-shouldered Hawks recovered, 109 (91.6%) moved 100 km (long-distance dispersers). Three (2.5%), all long-distance dispersers, were vagrants (recovered outside the species' range of residency), and were found 374 to 843 km northeast and south of their banding locations in the Mojave, Great Basin, and Vizcaino deserts. The distribution of directions of short-distance dispersal was bipolar, closely corresponding with the northwest—southeast orientation of the species' range in southern California, while that of long-distance dispersers was mainly to the north. One of 10 long-distance dispersers, a nonvagrant, survived well into the age of breeding (103.0 months), whereas eight of the other nine perished before 14.5 months. The implications of vagrancy for conservation of this resident subspecies are that a relatively small source area can contribute genetic material over a vastly larger receiving area but rarely does so because of high mortality rates. Nonetheless, the movements of vagrants we documented provide evidence for the species' potential to populate new landscapes in response to changing environmental conditions and to maintain genetic heterogeneity within existing populations.

The Condor↗
USGS2011

The influence of fine-scale habitat features on regional variation in population performance of alpine White-tailed Ptarmigan

It is often assumed (explicitly or implicitly) that animals select habitat features to maximize fitness. However, there is often a mismatch between preferred habitats and indices of individual and population measures of performance. We examined the influence of fine-scale habitat selection on the overall population performance of the White-tailed Ptarmigan (Lagopus leucura), an alpine specialist, in two subdivided populations whose habitat patches are configured differently. The central region of Vancouver Island, Canada, has more continuous and larger habitat patches than the southern region. In 2003 and 2004, using paired logistic regression between used (n = 176) and available (n = 324) sites, we identified food availability, distance to standing water, and predator cover as preferred habitat components . We then quantified variation in population performance in the two regions in terms of sex ratio, age structure (n = 182 adults and yearlings), and reproductive success (n = 98 females) on the basis of 8 years of data (1995-1999, 2002-2004). Region strongly influenced females' breeding success, which, unsuccessful hens included, was consistently higher in the central region (n = 77 females) of the island than in the south (n = 21 females, P = 0.01). The central region also had a much higher proportion of successful hens (87%) than did the south (55%, P < 0.001). In light of our findings, we suggest that population performance is influenced by a combination of fine-scale habitat features and coarse-scale habitat configuration. ?? The Cooper Ornithological Society 2011.

Condor↗
USGS2011

Local weather, regional climate, and annual survival of the northern spotted owl

We used an information-theoretical approach and Cormack—Jolly—Seber models for open populations in program MARK to examine relationships between survival rates of Northern Spotted Owls and a variety of local weather variables and long-term climate variables. In four of the six populations examined, survival was positively associated with wetter than normal conditions during the growing season or high summer temperatures. At the three study areas located at the highest elevations, survival was positively associated with winter temperature but also had a negative or quadratic relation with the number of storms and winter precipitation. A meta-analysis of all six areas combined indicated that annual survival was most strongly associated with phase shifts in the Southern Oscillation and Pacific Decadal Oscillation, which reflect large-scale temperature and precipitation patterns in this region. Climate accounted for a variable amount (1–41%) of the total process variation in annual survival but for more year-to-year variation (3–66%) than did spatial variation among owl territories (0–7%). Negative associations between survival and cold, wet winters and nesting seasons were similar to those found in other studies of the Spotted Owl. The relationships between survival and growing-season precipitation and regional climate patterns, however, had not been reported for this species previously. Climate-change models for the first half of the 21st century predict warmer, wetter winters and hotter, drier summers for the Pacific Northwest. Our results indicate that these conditions could decrease Spotted Owl survival in some areas.

Oregon, Washington↗
USGS2011

Postfledging survival of Grasshopper Sparrows in grasslands managed with fire and grazing

More accurate estimates of survival after nestlings fledge are needed for population models to be parameterized and population dynamics to be understood during this vulnerable life stage. The period after fledging is the time when chicks learn to fly, forage, and hide from predators. We monitored postfledging survival, causespecific mortality, and movements of Grasshopper Sparrows ( Ammodramus savannarum ) in grassland managed with fire and grazing. In 2009, we attached radio transmitters to 50 nestlings from 50 different broods and modeled their survival in response to climatic, biological, and ecological variables. There was no effect of treatment on survival. The factor most influencing postfledging survival was age; no other variable was significant. The majority of chicks (74%) died within 3 days of radio-transmitter attachment. We attributed most mortality to mesopredators (48%) and exposure (28%). Fledglings' movements increased rapidly for the first 4 days after they left the nest and were relatively stable for the remaining 10 days we tracked them. On average, fledglings took flight for the first time 4 days after fledging and flew &ge;10 m 9 days after fledging. Our data show that the Grasshopper Sparrow's survival rates may be less than most models relying on nest-success estimates predict, and we emphasize the importance of incorporating estimates of survival during the postfledging period in demographic models.

Iowa↗
USGS2011

Innate immunity is not related to the sex of adult Tree Swallows during the nestling period

Evolutionary theory predicts that exposure to more diverse pathogens will result in the evolution of a more robust immune response. We predicted that during the breeding season the innate immune function of female Tree Swallows ( Tachycineta bicolor ) should be more effective than that of males because (1) the transmission of sexually transmitted microbes during copulation puts females at greater risk because ejaculates move from males to females, (2) females copulate with multiple males, exposing them to the potentially pathogenic microbes in semen, and (3) females spend more time in the nest than do males so may be more exposed to nest microbes and ectoparasites that can be vectors of bacterial and viral pathogens. In addition, elevated testosterone in males may suppress immune function. We tested our prediction during the 2009 breeding season with microbicidal assays in vitro to assess the ability of the innate immune system to kill Escherichia coli . The sexes did not differ in the ability of their whole blood to kill E. coli . We also found no significant relationships between the ability of whole blood to kill E. coli and the reproductive performance or the physical condition of males or females. These results indicate that during the nestling period there are no sexual differences in this component of the innate immune system. In addition, they suggest that there is little association between this component of innate immunity and the reproductive performance and physical condition during the nestling period of adult Tree Swallows.

The Condor↗
USGS2011

Use of early-successional managed northern forest by mature-forest species during the post-fledging period

In eastern North America, after the young fledge, both adult and juvenile mature-forest birds may use regenerating clearcuts, although which species frequent early-successional forest and during which life stages is not well documented. To assess whether birds nesting in mature forest in north-central Minnesota use regenerating clearcuts 2&ndash;10 years old, we netted after birds fledged (2006&ndash;2009) and during the breeding season (2009). In addition, we monitored Ovenbird ( Seiurus aurocapilla ) nests and banded nestlings in adjacent mature forest and estimated the age at which juveniles used regenerating clearcuts. While banding, we also recorded nests of any species encountered opportunistically in regenerating clearcuts as evidence of breeding in this cover type. During July and August, we captured 4556 birds of 62 species, of which 1746 (38%) were of 28 mature-forest species. As reported elsewhere, most (76%) mature-forest birds we captured were of only a few species: Ovenbird, American Redstart ( Setophaga ruticilla ), Least Flycatcher ( Empidonax minimus ), and Black-and-white Warbler ( Mniotilta varia ). In 2009, 21% of captures during the nesting period were of mature-forest birds. Comparing dates of fledging from monitored nests to dates of capture in clearcuts implies that nearly all (95%) hatch-year Ovenbirds using clearcuts were independent of adult care. Capture dates of juveniles of other mature-forest species were similar. Although we captured 340 hatch-year Ovenbirds in regenerating clearcuts, we captured only one of 424 Ovenbirds we had banded as nestlings in adjacent mature forest. Within the clearcuts, we encountered nests of five species that typically nest in mature forest.

Minnesota↗
USGS2011

Nest predation and circulating corticosterone levels within and among species

Variation in the risk of predation to offspring can influence the expression of reproductive strategies both within and among species. Appropriate expression of reproductive strategies in environments that differ in predation risk can have clear advantages for fitness. Although adult-predation risk appears to influence glucocorticosteroid levels, leading to changes in behavioral and life-history strategies, the influence of offspring-predation risk on adult glucocorticosteroid levels remains unclear. We compared total baseline corticosterone concentrations in Gray-headed Juncos (Junco hyemalis dorsalis) nesting on plots with and without experimentally reduced risk of nest predation. Despite differences in risk between treatments, we failed to find differences in total baseline corticosterone concentrations. When we examined corticosterone concentrations across a suite of sympatric species, however, higher risk of nest predation correlated with higher total baseline corticosterone levels. As found previously, total baseline corticosterone was negatively correlated with body condition and positively correlated with date of sampling. However, we also found that corticosterone levels increased seasonally, independent of stage of breeding. Nest predation can alter the expression of birds' reproductive strategies, but our findings suggest that total baseline corticosterone is not the physiological mechanism regulating these responses.

The Condor↗
USGS2012

Bird-habitat relationships in interior Columbia Basin shrubsteppe

Vegetation structure is considered an important habitat feature structuring avian communities. In the sagebrush biome, both remotely-sensed and field-acquired measures of big sagebrush (Artemisia tridentata) cover have proven valuable in understanding avian abundance. Differences in structure between the exotic annual cheatgrass (Bromus tectorum) and native bunchgrasses are also expected to be important. We used avian abundance data from 318 point count stations, coupled with field vegetation measurements and a detailed vegetation map, to model abundance for four shrub- and four grassland-associated avian species in southeastern Washington shrubsteppe. Specifically, we ask whether species distinguish between bunchgrass and cheatgrass, and whether mapped, categorical cover types adequately explain species' abundance or whether fine-grained, field-measured differences in vegetation cover are also important. Results indicate that mapped cover types alone can be useful for predicting patterns of distribution and abundance within the sagebrush biome for several avian species (five of eight studied here). However, field-measured sagebrush cover was a strong positive predictor for Sage Sparrow (Amphispiza belli), the only sagebrush obligate in this study, and a strong negative predictor for two grassland associates, Horned Lark (Eremophila alpestris) and Grasshopper Sparrow (Ammodramus savannarum). Likewise, shrub associates did not differ in abundance in sagebrush with a cheatgrass vs. bunchgrass understory, but grassland associates were more common in either bunchgrass (Horned Lark and Grasshopper Sparrow) or cheatgrass grasslands (Long-billed Curlew, Numenius americanus), or tended to use sagebrush-cheatgrass less than sagebrush-bunchgrass (Horned Lark, Grasshopper Sparrow, and Savannah Sparrow, Passerculus sandwichensis).

The Condor↗