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At least 181 records · Page 10Linked to original sources
USGS2009

Mechanisms of population heterogeneity among molting common mergansers on Kodiak Island, Alaska: Implications for genetic assessments of migratory connectivity

Quantifying population genetic heterogeneity within nonbreeding aggregations can inform our understanding of patterns of site fidelity, migratory connectivity, and gene flow between breeding and nonbreeding areas. However, characterizing mechanisms that contribute to heterogeneity, such as migration and dispersal, is required before site fidelity and migratory connectivity can be assessed accurately. We studied nonbreeding groups of Common Mergansers ( Mergus merganser ) molting on Kodiak Island, Alaska, from 2005 to 2007, using banding data to assess rates of recapture, mitochondrial (mt) DNA to determine natal area, and nuclear microsatellite genotypes to assess dispersal. Using baseline information from differentiated mtDNA haplogroups across North America, we were able to assign individuals to natal regions and document population genetic heterogeneity within and among molting groups. Band-recovery and DNA data suggest that both migration from and dispersal among natal areas contribute to admixed groups of males molting on Kodiak Island. A lack of differentiation in the Common Merganser's nuclear, bi-parentally inherited DNA, observed across North America, implies that dispersal can mislead genetic assessments of migratory connectivity and assignments of nonbreeding individuals to breeding areas. Thus multiple and independent data types are required to account for such behaviors before accurate assessments of migratory connectivity can be made.

Alaska↗
USGS2009

Postfledging Forster's Tern movements, habitat selection, and colony attendance in San Francisco Bay

Relatively little is known about birds during the postfledging period when flighted chicks have left the nest and must learn to forage independently. We examined postfledging movements, habitat selection, and colony attendance of Forster's Terns (Sterna forsteri) radio-marked just before they fledged in San Francisco Bay, California. The proportion of the day spent at their natal colony declined as juveniles aged, from 65% at the time of fledging to <5% within two weeks of fledging. Accordingly, the distance postfledging terns were located from their colony increased as they aged, from <500 m within the first week of fledging to >5000 m by their fifth week. Time of day also influenced colony attendance, with older terns spending more time at the colony during nighttime hours (20:00 to 05:00) than during the day (06:00 to 19:00), when they were presumably foraging. Home ranges and core-use areas averaged 12.14 km 2 and 2.23 km 2 , respectively. At each of four spatial scales of analysis, postfledging terns selected salt pond habitats strongly. No other habitat types were selected at any scale, but terns consistently avoided tidal flats and uplands. Terns also avoided open bay habitats at the two largest spatial scales, tidal marsh habitats at the two smallest scales, and sloughs and managed marshes at several scales. Within salt ponds, terns were located closer to salt-pond levees (58 m) than was expected (107 m). Our results indicate that tern chicks disperse from their natal colony within a few weeks of fledging, with older chicks using their natal colony primarily for roosting during the night, and that postfledging terns are highly dependent on salt ponds. ?? 2009 by The Cooper Ornithological Society. All rights reserved.

Condor↗
USGS2009

Effects of an unseasonable snowstorm on red-faced Warbler nesting success

Earlier initiation of nests by breeding birds may reflect an adaptive response to changes in food availability or warming of spring temperatures, but the consequences of initiating nests too early may be severe, particularly at high elevations. A rare snowstorm in late May 2008 resulted in nest abandonment by 68% of Red-faced Warblers (Cardellina rubrifrons) breeding in a high-elevation riparian ecosystem of southeastern Arizona. In addition, climate data from our study site from 1950 to 2008 revealed higher-than-average springtime temperatures during the past 10 years. If birds respond to this increase in springtime temperatures by nesting earlier their vulnerability to spring snowstorms may increase. ?? 2009 by The Cooper Ornithological Society. All rights reserved.

Condor↗
USGS2009

Multiple spring migration strategies in a population of Pacific Common Eiders

Spring migration strategies vary within and among species. Examination of this variability extends our understanding of life histories and has implications for conservation. I used satellite transmitters to determine migration strategies and evaluate factors influencing the timing of spring migration of Pacific Common Eiders (Somateria mollissima v-nigrum) that nest along the western Beaufort Sea coast. Adult females were marked at nesting colonies in the summers of 2000, 2001, and 2003, and were followed throughout spring migration the following year. Each year approximately equal proportions of eiders used three distinct migration strategies varying in duration, staging locations (waters near the Chukotka Peninsula, Russia, and the Chukchi and Beaufort seas, Alaska), and arrival dates at the nesting areas. It is unlikely that differences in the timing of movements to stopover sites in the Chukchi and Beaufort seas were a result of responses to changes in weather, particularly wind direction. Ice distribution and melt/movement patterns vary substantially among staging areas and thus may affect risk of starvation and reproductive potential. Long-term (decadal) changes in climate may favor birds using one strategy during "warmer" and another during "colder" years. ?? 2009 by The Cooper Ornithological Society. All rights reserved.

Condor↗
USGS2009

Meeting reproductive demands in a dynamic upwelling system: Foraging strategies of a pursuit-diving seabird, the marbled murrelet

Seabirds maintain plasticity in their foraging behavior to cope with energy demands and foraging constraints that vary over the reproductive cycle, but behavioral studies comparing breeding and nonbreeding individuals are rare. Here we characterize how Marbled Murrelets (Brachyramphus marmoratus) adjust their foraging effort in response to changes in reproductive demands in an upwelling system in central California. We radio-marked 32 murrelets of known reproductive status (9 breeders, 12 potential breeders, and 11 nonbreeders) and estimated both foraging ranges and diving rates during the breeding season. Murrelets spent more time diving during upwelling than oceanographic relaxation, increased their foraging ranges as the duration of relaxation grew longer, and reduced their foraging ranges after transitions to upwelling. When not incubating, murrelets moved in a circadian pattern, spending nighttime hours resting near flyways used to reach nesting habitat and foraging during the daytime an average of 5.7 km (SD 6.7 km) from nighttime locations. Breeders foraged close to nesting habitat once they initiated nesting and nest attendance was at a maximum, and then resumed traveling longer distances following the completion of nesting. Nonbreeders had similar nighttime and daytime distributions and tended to be located farther from inland flyways. Breeders increased the amount of time they spent diving by 71-73% when they had an active nest by increasing the number of dives rather than by increasing the frequency of anaerobiosis. Thus, to meet reproductive demands during nesting, murrelets adopted a combined strategy of reducing energy expended commuting to foraging sites and increasing aerobic dive rates. ?? 2009 by The Cooper Ornithological Society. All rights reserved.

Condor↗
USGS2009

Fledging success is a poor indicator of the effects of bird blow flies on ovenbird survival

Infestations of bird blow flies ( Protocalliphora spp. and Trypocalliphora braueri ) have various negative effects on the condition of nestling birds. In the absence of other stressors such as inclement weather, however, infestation alone rarely reduces fledging success. Previous studies have documented effects of blow flies on nestling condition and fledging success. Without information regarding fledgling survival, the full effect of blow-fly infestation remains unclear. To fully investigate the effect of blow-fly infestation on reproductive success of the Ovenbird ( Seiurus aurocapilla ), we monitored infested and non-infested nests and monitored fledglings from each by using radio telemetry. Blow flies did not affect birds during the nestling period, as brood size, mean nestling mass, fledging success, and time to fledging in infested and non-infested nests were no different. Fledgling survival and minimum distance traveled the first day after fledging, however, were significantly lower for infected fledglings than for those that were not infected. We conclude that the stress of the early fledgling period combined with recent or concurrent blow-fly infection increases mortality in young Oven-birds. Our results demonstrate the importance of including the post-fledging period in investigations of the effects of ectoparasitic infestations on birds.

Minnesota↗
USGS2009

Landbird migration in the American West: Recent progress and future research directions

Our knowledge of avian behaviors during the nonbreeding period still lags behind that of the breeding season, but the last decade has witnessed a proliferation in research that has yielded significant progress in understanding migration patterns of North American birds. And, although historically the great majority of migration research has been conducted in the eastern half of the continent, there has been much recent progress on aspects of avian migration in the West. In particular, expanded use of techniques such as radar, plasma metabolites, mist-netting, count surveys, stable isotopes, genetic data, and animal tracking, coupled with an increase in multi-investigator collaborations, have all contributed to this growth of knowledge. There is increasing recognition that migration is likely the most limiting time of year for migratory birds, increasing the importance of continuing to decipher patterns of stopover ecology, identifying critical stopover habitats, and documenting migration routes in the diverse and changing landscapes of the American West. Here, we review and briefly synthesize the latest findings and advances in avian migration and consider research needs to guide future research on migration in the West. ?? 2009 by The Cooper Ornithological Society. All rights reserved.

The Condor↗
USGS2009

Environmental and human influences on trumpeter swan habitat occupancy in Alaska

Approximately 70-80% of the entire population of the Trumpeter Swan (Cygnus huccinator) depends for reproduction on wetlands in Alaska. This makes the identification of important habitat features and the effects of human interactions important for the species' long-term management. We analyzed the swan's habitat preferences in five areas throughout the state and found that swan broods occupied some wetland types, especially larger closed-basin wetlands such as lakes and ponds, at rates much higher than they occupied other wetland types, such as shrubby or forested wetlands. We also found a negative effect of transportation infrastructure on occupancy by broods in and around the Minto Flats State Game Refuge, Kenai National Wildlife Refuge, and Tetlin National Wildlife Refuge. This finding is of particular interest because much of the Minto Flats refuge has recently been licensed for oil and gas exploration and parts of the Kenai refuge have been developed in the past. We also investigated the potential effects of the shrinkage of closed-basin ponds on habitat occupancy by nesting Trumpeter Swans. We compared nesting swans' use of ponds with changes in the ponds' size and other characteristics from 1982 to 1996 and found no relationships between occupancy and changes in pond size. However, we believe that the recent and rapid growth of Trumpeter Swan populations in Alaska may become limited by available breeding habitat, and anthropogenic and climate-induced changes to the swan's breeding habitats have the potential to limit future production. ?? 2009 by The Cooper Ornithological Society. All rights reserved.

Condor↗
USGS2009

Avian response to wildfire in interior Columbia basin shrubsteppe

Wildfire and conversion of sagebrush (Artemisia spp.) shrublands to cheatgrass (Bromus tectorum) grasslands is a serious threat to the shrubsteppe ecosystem, but few studies have documented wildfire's effects on birds with multiple years of pre- and post-fire data. Using data from avian point counts recorded 4 years before and 7 years after a large-scale, severe wildfire in the Columbia Basin of south-central Washington, we found significant effects of fire on population trends or mean abundance of nearly all species investigated. The Sage Sparrow (Amphispiza belli), a sagebrush obligate, was decreasing at a high rate both pre- and post-fire. Among species inhabiting more open shrubsteppe or grasslands, the mean abundance of three (Grasshopper Sparrow, Ammodramus savannarum; Western Meadowlark, Sturnella neglecta; Vesper Sparrow, Pooecetes gramineus) was lower post-fire and one (Lark Sparrow, Chondestes grammacus) showed an initial, but short-lived, increase post-fire before dropping below pre-fire levels. Only one (Horned Lark, Eremophila alpestris) increased steadily post-fire and had higher post-fire mean abundance. ?? 2009 by The Cooper Ornithological Society. All rights reserved.

Condor↗
USGS2010

Population trends of forest birds at Hakalau Forest National Wildlife Refuge, Hawai'i

The Hakalau Forest National Wildlife Refuge was established to protect native Hawaiian forest birds, particularly endangered species. Management for forest restoration on the refuge has consisted mainly of removing feral ungulates, controlling invasive alien plants, and reforesting former pastures. To assess effects of this habitat improvement for forest birds, we estimated density annually by distance sampling and examined population trends for native and alien passerines over the 21 years since the refuge was established. We examined long-term trends and recent short-term trajectories in three study areas: (1) reforested pastureland, (2) heavily grazed open forest that was recovering, and (3) lightly grazed closed forest that was relatively intact. Three species of native birds and two species of alien birds had colonized the reforested pasture and were increasing. In the open forest, densities of all eight native species were either stable or increasing. Long-term trends for alien birds were also generally stable or increasing. Worryingly, however, during the most recent 9 years, in the open forest trajectories of native species were decreasing or inconclusive, but in the reforested pasture they generally increased. The closed forest was surveyed in only the most recent 9 years, and trajectories of native species there were mixed. Overall, long-term population trends in Hakalau are stable or increasing, contrasting with declines in most other areas of Hawai'i over the same period. However, more recent mixed results may indicate emergent problems for this important bird area.

Hawai'i↗
USGS2010

Abdominally implanted transmitters with percutaneous antennas affect the dive performance of Common Eiders

Implanted transmitters have become an important tool for studying the ecology of sea ducks, but their effects remain largely undocumented. To address this, we assessed how abdominally implanted transmitters with percutaneous antennas affect the vertical dive speeds, stroke frequencies, bottom time, and dive duration of captive Common Eiders ( Somateria mollissima ). To establish baselines, we recorded video of six birds diving 4.9 m prior to surgery, implanted them with 38- to 47-g platform transmitter terminals, and then recorded their diving for 3.5 months after surgery to determine effects. Descent speeds were 16&ndash;25% slower and ascent speeds were 17&ndash;44% slower after surgery, and both remained below baseline at the end of the study. Dive durations were longer than baseline until day 22. On most days between 15 and 107 days after surgery, foot-stroke frequencies of birds foraging on the bottom were slower. Foot- and wing-stroke frequencies during descent and bottom time did not differ across the time series. If birds that rely on benthic invertebrates for sustenance dive slower and stay submerged longer after being implanted with a satellite transmitter, their foraging energetics may be affected. Researchers considering use of implanted transmitters with percutaneous antennas should be mindful of these effects and the possibility of concomitant alterations in diving behavior, foraging success, and migratory behavior compared to those of unmarked conspecifics.

Alaska↗
USGS2010

Exposure of nonbreeding migratory shorebirds to cholinesterase-inhibiting contaminants in the western hemisphere

Migratory shorebirds frequently forage and roost in agricultural habitats, where they may be exposed to cholinesterase-inhibiting pesticides. Exposure to organophosphorus and carbamate compounds, common anti-cholinesterases, can cause sublethal effects, even death. To evaluate exposure of migratory shorebirds to organophosphorus and carbamates, we sampled birds stopping over during migration in North America and wintering in South America. We compared plasma cholinesterase activities and body masses of individuals captured at sites with no known sources of organophosphorus or carbamates to those captured in agricultural areas where agrochemicals were recommended for control of crop pests. In South America, plasma acetylcholinesterase and butyrylcholinesterase activity in Buff-breasted Sandpipers was lower at agricultural sites than at reference sites, indicating exposure to organophosphorus and carbamates. Results of plasma cholinesterase reactivation assays and foot-wash analyses were inconclusive. A meta-analysis of six species revealed no widespread effect of agricultural chemicals on cholinesterase activity. however, four of six species were negative for acetylcholinesterase and one of six for butyrylcholinesterase, indicating negative effects of pesticides on cholinesterase activity in a subset of shorebirds. Exposure to cholinesterase inhibitors can decrease body mass, but comparisons between treatments and hemispheres suggest that agrochemicals did not affect migratory shorebirds' body mass. Our study, one of the first to estimate of shorebirds' exposure to cholinesterase-inhibiting pesticides, suggests that shorebirds are being exposed to cholinesterase- inhibiting pesticides at specific sites in the winter range but not at migratory stopover sites. future research should examine potential behavioral effects of exposure and identify other potential sitesand levels of exposure. ?? The Cooper Ornithological Society 2010.

Condor↗
USGS2010

Space use and habitat selection of migrant and resident American Avocets in San Francisco Bay

San Francisco Bay is a wintering area for shorebirds, including American Avocets (Recurvirostra americana). Recently, a new resident population of avocets has emerged, presumably because of the development of tidal marshes into salt-evaporation ponds. In habitat restoration now underway, as many as 90% of salt ponds will be restored to tidal marsh. However, it is unknown if wintering and resident avocets coexist and if their requirements for space and habitat differ, necessitating different management for their populations to be maintained during restoration. We captured and radio-marked wintering avocets at a salt pond and a tidal flat to determine their population status (migrant or resident) and examine their space use and habitat selection. Of the radio-marked avocets, 79% were migrants and 21% were residents. At the salt pond, residents' fidelity to their location of capture was higher, and residents moved less than did migrants from the same site. Conversely, on the tidal flat, fidelity of residents to their site of capture was lower, and residents' home ranges were larger than those of migrants from the same site. Habitat selection of migrants and residents differed little; however, capture site influenced habitat selection far more than the birds' status as migrants or residents. Our study suggests that individual avocets have high site fidelity while wintering in San Francisco Bay, although the avocet as a species is plastic in its space use and habitat selection. This plasticity may allow wintering migrant and resident avocets to adapt to habitat change in San Francisco Bay. ?? The Cooper Ornithological Society 2010.

Condor↗
USGS2010

Accuracy of egg flotation throughout incubation to determine embryo age and incubation day in waterbird nests

Floating bird eggs to estimate their age is a widely used technique, but few studies have examined its accuracy throughout incubation. We assessed egg flotation for estimating hatch date, day of incubation, and the embryo's developmental age in eggs of the American Avocet ( Recurvirostra americana ), Black-necked Stilt ( Himantopus mexicanus ), and Forster's Tern ( Sterna forsteri ). Predicted hatch dates based on egg flotation during our first visit to a nest were highly correlated with actual hatch dates ( r = 0.99) and accurate within 2.3 ± 1.7 (SD) days. Age estimates based on flotation were correlated with both day of incubation ( r = 0.96) and the embryo's developmental age ( r = 0.86) and accurate within 1.3 ± 1.6 days and 1.9 ± 1.6 days, respectively. However, the technique's accuracy varied substantially throughout incubation. Flotation overestimated the embryo's developmental age between 3 and 9 days, underestimated age between 12 and 21 days, and was most accurate between 0 and 3 days and 9 and 12 days. Age estimates based on egg flotation were generally accurate within 3 days until day 15 but later in incubation were biased progressively lower. Egg flotation was inaccurate and overestimated embryo age in abandoned nests (mean error: 7.5 ± 6.0 days). The embryo's developmental age and day of incubation were highly correlated ( r = 0.94), differed by 2.1 ± 1.6 days, and resulted in similar assessments of the egg-flotation technique. Floating every egg in the clutch and refloating eggs at subsequent visits to a nest can refine age estimates.

The Condor↗
USGS2010

Comparative morphology among northern populations of breeding Cooper's Hawks

Few studies at a broad geographical scale have characterized intraspecific variation in morphology of woodland hawks in the genus Accipiter . From 1999 to 2007 we investigated morphological variation in large samples of live Cooper's Hawks ( A. cooperii ) nesting in four study areas: coniferous woodland around Victoria, British Columbia, Canada, isolated deciduous woodlands in short-grass prairies of northwestern North Dakota, towns and rural deciduous woodlands along the border of North Dakota and Minnesota, and urban and rural mixed deciduous and coniferous landscapes of Wisconsin. These sites span 2660 km across the northern part of the species' breeding range. We measured body mass (i.e., size), wing chord, tail length, tarsus diameter, hallux length, and culmen length of breeding adults, finding significant and clinal variation in body mass (or size). The smallest and most similar-sized birds occurred in British Columbia and western North Dakota, larger birds along the border between North Dakota and Minnesota, and the largest birds in Wisconsin. Several other characters varied significantly when mass was used as a covariate. Variation by study site in mean indices of sexual size dimorphism was negligible and not significant. We speculate that the morphological differences we found, in part, are the result of geographic isolation, where diets, migratory behavior, and structural characteristics of nesting habitats vary across landscape types.

British Columbia, Minnesota, North Dakota, Wiscons↗
USGS2010

Regional Variation in mtDNA of the Lesser Prairie-Chicken

Cumulative loss of habitat and long-term decline in the populations of the Lesser Prairie-Chicken ( Tympanuchus pallidicinctus ) have led to concerns for the species' viability throughout its range in the southern Great Plains. For more efficient conservation past and present distributions of genetic variation need to be understood. We examined the distribution of mitochondrial DNA (mtDNA) variation in the Lesser Prairie-Chicken across Kansas, Colorado, Oklahoma, and New Mexico. Throughout the range we found little genetic differentiation except for the population in New Mexico, which was significantly different from most other publications. We did, however, find significant isolation by distance at the rangewide scale ( r =0.698). We found no relationship between haplotype phylogeny and geography, and our analyses provide evidence for a post-glacial population expansion within the species that is consistent with the idea that speciation within Tympanuchus is recent. Conservation actions that increase the likelihood of genetically viable populations in the future should be evaluated for implementation.

Texas, Colorado, Kansas, New Mexico, Oklahoma↗
USGS2010

Are there optimal densities for prairie birds?

The major forces of food and predation shape fitness-enhancing decisions of birds at all stages of their life cycles. During the breeding season, birds can minimize nest loss due to predation by selecting sites with a lower probability of predation. To understand the environmental and social aspects and consequences of breedingsite selection in prairie birds, we explored variation in nest-survival patterns of the Lark Bunting (Calamospiza melanocorys) in the shortgrass prairie region of North America. Over four breeding seasons, we documented the survival of 405 nests, conducted 60 surveys to estimate bird densities, and measured several vegetative features to describe habitat structure in 24 randomly selected study plots. Nest survival varied with the buntings' density as described by a quadratic polynomial, increasing with density below 1.5 birds ha -1 and decreasing with density between 1.5 and 3 birds ha -1 , suggesting that an optimal range of densities favors reproductive success of the Lark Bunting, which nests semi-colonially. Nest survival also increased with increasing vegetation structure of study plots and varied with age of the nest, increasing during early incubation and late in the nestling stage and declining slightly from mid-incubation to the middle of the nestling period. The existence of an optimal range of densities in this semi-colonial species can be elucidated by the "commodity-selection hypothesis" at low densities and density dependence at high densities. ?? The Cooper Ornithological Society 2010.

Condor↗
USGS2010

Trace elements have limited utility for studying migratory connectivity in shorebirds that winter in Argentina

Trace-element analysis has been suggested as a tool for the study of migratory connectivity because (1) trace-element abundance varies spatially in the environment, (2) trace elements are assimilated into animals' tissues through the diet, and (3) current technology permits the analysis of multiple trace elements in a small tissue sample, allowing the simultaneous exploration of several elements. We explored the potential of trace elements (B, Na, Mg, Al, Si, P, S, K, Ca, Ti, Cr, Mn, Ni, Cu, Zn, As, Sr, Cs, Hg, Tl, Pb, Bi, Th, and U) to clarify the migratory connectivity of shorebirds that breed in North America and winter in southern South America. We collected 66 recently replaced secondary feathers from Red Knots (Calidris canutus) at three sites in Patagonia and 76 from White-rumped Sandpipers (C. fuscicollis) at nine sites across Argentina. There were significant differences in trace-element abundance in shorebird feathers grown at different nonbreeding sites, and annual variability within a site was small compared to variability among sites. Across Argentina, there was no large-scale gradient in trace elements. The lack of such a gradient restricts the application of this technique to questions concerning the origin of shorebirds to a small number of discrete sites. Furthermore, our results including three additional species, the Pectoral Sandpiper (C. melanotos), Wilson's Phalarope (Phalaropus tricolor), and Collared Plover (Charadrius collaris), suggest that trace-element profiles change as feathers age. Temporal instability of trace-element values could undermine their application to the study of migratory connectivity in shorebirds. ?? The Cooper Ornithological Society 2010.

Condor↗