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Bohrer G.,Ohio State University | Brandes D.,Lafayette College | Mandel J.T.,Advanced Conservation Strategies | Bildstein K.L.,Acopian Center for Conservation Learning | And 5 more authors.
Ecology Letters | Year: 2012

Soaring birds migrate in massive numbers worldwide. These migrations are complex and dynamic phenomena, strongly influenced by meteorological conditions that produce thermal and orographic uplift as the birds traverse the landscape. Herein we report on how methods were developed to estimate the strength of thermal and orographic uplift using publicly available digital weather and topography datasets at continental scale. We apply these methods to contrast flight strategies of two morphologically similar but behaviourally different species: golden eagle, Aquila chrysaetos, and turkey vulture, Cathartes aura, during autumn migration across eastern North America tracked using GPS tags. We show that turkey vultures nearly exclusively used thermal lift, whereas golden eagles primarily use orographic lift during migration. It has not been shown previously that migration tracks are affected by species-specific specialisation to a particular uplift mode. The methods introduced herein to estimate uplift components and test for differences in weather use can be applied to study movement of any soaring species. © 2011 Blackwell Publishing Ltd/CNRS.


Ferrer M.,CSIC - Doñana Biological Station | Bildstein K.,Acopian Center for Conservation Learning | Penteriani V.,CSIC - Doñana Biological Station | Casado E.,Fundacion Migres | de Lucas M.,CSIC - Doñana Biological Station
PLoS ONE | Year: 2011

Background: Island faunas have played central roles in the development of evolutionary biology and ecology. Birds are among the most studied organisms on islands, in part because of their dispersal powers linked to migration. Even so, we lack of information about differences in the movement ecology of island versus mainland populations of birds. Methodology/Principal Findings: Here we present a new general pattern indicating that large birds with deferred sexual maturity are sedentary on islands, and that they become so even when they are migratory on the mainland. Density-dependent variation in the age at first breeding affects the survivorship of insular populations and this, in turn, affects the movement ecology of large birds. Because density-dependent variation in the age of first breeding is critical to the long-term survival of small isolated populations of long-lived species, migratory forms can successfully colonize islands only if they become sedentary once there. Analyses of the movement ecology of continental and insular populations of 314 species of raptors, 113 species of Ciconiiformes and 136 species of passerines, along with individual-based population simulations confirm this prediction. Conclusions: This finding has several consequences for speciation, colonization and survival of small isolated population of species with deferred sexual maturity. © 2011 Ferrer et al.


Therrien J.-F.,Acopian Center for Conservation Learning | Gauthier G.,Laval University | Korpimaki E.,University of Turku | Bety J.,University of Quebec at Rimouski
Ecology | Year: 2014

Predation has been suggested to be especially important in simple food webs and less productive ecosystems such as the arctic tundra, but very few data are available to evaluate this hypothesis. We examined the hypothesis that avian predators could drive the population dynamics of two cyclic lemming species in the Canadian Arctic. A dense and diverse suite of predatory birds, including the Snowy Owl (Bubo scandiacus), the Rough-legged Hawk (Buteo lagopus), and the Long-tailed Jaeger (Stercorarius longicaudus), inhabits the arctic tundra and prey on collared (Dicrostonyx groenlandicus) and brown (Lemmus trimucronatus) lemmings during the snow-free period. We evaluated the predation pressure exerted by these predators by combining their numerical (variation in breeding and fledgling numbers) and functional (variation in diet and daily consumption rates) responses to variations in lemming densities over the 2004-2010 period. Breeding density and number of fledglings produced by the three main avian predators increased sharply without delay in response to increasing lemming densities. The proportion of collared lemmings in the diet of those predators was high at low lemming density (both species) but decreased as lemming density increased. However, we found little evidence that their daily consumption rates vary in relation to changes in lemming density. Total consumption rate by avian predators initially increased more rapidly for collared lemming but eventually leveled off at a much higher value for brown lemmings, the most abundant species at our site. The combined daily predation rate of avian predators exceeded the maximum daily potential growth rates of both lemming species except at the highest recorded densities for brown lemmings. We thus show, for the first time, that predation pressure exerted without delay by avian predators can limit populations of coexisting lemming species during the snow-free period, and thus, that predation could play a role in the cyclic dynamic of these species in the tundra. © 2014 by the Ecological Society of America.


Kendall C.J.,Princeton University | Virani M.Z.,Ornithology Section | Hopcraft J.G.C.,Frankfurt Zoological Society | Bildstein K.L.,Acopian Center for Conservation Learning | Rubenstein D.I.,Princeton University
PLoS ONE | Year: 2014

The ongoing global decline in vulture populations raises major conservation concerns, but little is known about the factors that mediate scavenger habitat use, in particular the importance of abundance of live prey versus prey mortality. We test this using data from the Serengeti-Mara ecosystem in East Africa. The two hypotheses that prey abundance or prey mortality are the main drivers of vulture habitat use provide alternative predictions. If vultures select areas based only on prey abundance, we expect tracked vultures to remain close to herds of migratory wildebeest regardless of season. However, if vultures select areas where mortality rates are greatest then we expect vultures to select the driest regions, where animals are more likely to die of starvation, and to be attracted to migratory wildebeest only during the dry season when wildebeest mortality is greatest. We used data from GSM-GPS transmitters to assess the relationship between three vulture species and migratory wildebeest in the Mara-Serengeti ecosystem. Results indicate that vultures preferentially cluster around migratory herds only during the dry season, when herds experience their highest mortality. Additionally during the wet season, Ruppell's and Lappet-faced vultures select relatively dry areas, based on Normalized Difference Vegetation Index, whereas White-backed vultures preferred wetter areas during the wet season. Differences in habitat use among species may mediate coexistence in this scavenger guild. In general, our results suggest that prey abundance is not the primary driver of avian scavenger habitat use. The apparent reliance of vultures on non-migratory ungulates during the wet season has important conservation implications for vultures in light of on-going declines in non-migratory ungulate species and use of poisons in unprotected areas. © 2014 Kendall et al.


Gavashelishvili A.,Ilia State University | McGrady M.,Natural Research Ltd | Ghasabian M.,Armenian National Academy of Sciences | Bildstein K.L.,Acopian Center for Conservation Learning
Bird Study | Year: 2012

Capsule Juvenile and immature Cinereous Vultures from the Caucasus move large distances across undeveloped open-dry habitats in response to snowfall or high summer temperatures. Aim To study local and long-range movements of Cinereous Vulture (Aegypius monachus), and investigate the influence of environmental variables on spatial and temporal distributions of the species on a large scale. Methods We use 4-year-long location data from 6 juvenile Cinereous Vultures fitted with satellite-received transmitters to track their movements and obtain habitat suitability models. Results A few months after fledging, Cinereous Vultures may migrate from the Caucasus as far south as the Arabian Peninsula. Their movements are concentrated in undeveloped open-dry habitats. High temperatures push the vultures to higher latitudes and altitudes, while reverse seasonal movements are triggered by the extent of snow cover. Conclusions Our study shows the importance of the Arabian Peninsula and Iran as wintering areas for Cinereous Vultures. Long-distance movements by immature cinereous vultures are determined by climate seasonality, and in light of climate-warming scenarios for the next 100 years, there might be a shift in timing of the onset of the species seasonal movements and a change in the duration and geography of its wintering and summering. © 2012 Copyright British Trust for Ornithology.


Bildstein K.L.,Acopian Center for Conservation Learning | Peterjohn B.G.,U.S. Geological Survey
Journal of Raptor Research | Year: 2012

The future of conventional banding in raptor science depends upon the types of questions asked by scientists working in the field, and the extent to which banders and researchers continue their trapping and banding efforts. Traditionally, banding data have played two important roles in raptor science: assessing demographic statistics, including age at first breeding, survival rates, and mortality factors; and tracking movements of raptors, including migration, nomadic movements, and both natal and breeding dispersal. Recent decades have seen an explosive development and use of newer techniques to document the movements of raptors, including color leg-bands, wing-tags, conventional VHF tracking units, satellite-based UHF units, GPS-GSM units, and geolocating data loggers. All of these techniques have greatly facilitated our ability to track the movements of individual birds, broadening the field of movement ecology considerably, and shifting its emphasis from traditional population studies of migration toward detailed investigations of the ecology and geography of individual birds. Although conventional banding no longer plays as large a role in the study of raptor movements as it once did, its continued use can significantly complement the newer tools in use today, and can enhance our ability to understand the demographics and movements of raptors. For example, given banding's multi-decadal history, one potential use of banding data is in the assessment of the long-term effects of environmental changes, including climate, land-use, and contaminant changes, on both raptor demographics and movements. We believe that conventional banding remains an essential tool, for both the population biologist and the ecologist studying raptor movements, and that its usefulness in the field continues. We recommend that the emphasis of banding shift from short-term independent projects aimed at documenting movement patterns toward collaborative long-term efforts designed to provide insights into the factors influencing population responses to changing environments. © 2012 The Raptor Research Foundation, Inc.


Farmer C.J.,Acopian Center for Conservation Learning | Smith J.P.,HawkWatch International Inc.
Journal of Raptor Research | Year: 2010

Long-term monitoring is important for ensuring effective conservation of raptor populations. Raptors also can serve as indicators of biodiversity and ecosystem condition. Therefore, effective monitoring of raptor populations yields the added benefit of helping to evaluate the status of ecosystems. Spring counts of migrating raptors at concentration points may contribute to these goals, particularly by providing insight into the vital demographic rates underlying population trends. Although much is known about the monitoring value of autumn migration counts in North America, little research has addressed the value of spring counts. We compared counts at seven spring watchsites to those at seven autumn watchsites matched by region (Southwest, Great Lakes, and Northeast) to assess the value of spring counts for population monitoring. Our analyses suggested that population indexes derived from spring migration counts provided estimates of population change that differed overall from autumn migration counts in the same region. The concordance of spring and autumn trends was higher in the Southwest and Northeast than in the Great Lakes region, suggesting greater variation in the seasonal representation of populations in the latter region. The average precision of spring trend estimates was better than for autumn estimates in the same region in two of three regions, and the estimated rates of change often were lower in spring. Spring counts enhanced the ability to estimate population trends for species that are less common in autumn counts, including the Rough-legged Hawk (Buteo lagopus) and Red-shouldered Hawk (B. lineatus). To realize fully the value of spring counts, we recommend the establishment of additional spring watchsites in areas that concentrate migrants in autumn, but do so to a lesser extent in spring, as well as additional research to define the populations sampled by autumn and spring counts. © 2010 The Raptor Research Foundation, Inc.


Bernard M.J.,Pennsylvania State University | Goodrich L.J.,Acopian Center for Conservation Learning | Tzilkowski W.M.,Pennsylvania State University | Brittingham M.C.,Pennsylvania State University
Auk | Year: 2011

We investigated territory-level habitat use patterns of 132 color-banded male Ovenbirds (Seiurus aurocapilla) over a 12-year period at Hawk Mountain Sanctuary in eastern Pennsylvania. Our primary goals were to test hypotheses concerning selection behavior as well as to describe territory fidelity of an area-sensitive Neotropical migrant by quantifying year-to-year movements of individuals over a period equivalent to several generations. Furthermore, we tested whether returns and territory shifts were associated with prior reproductive success and bird age. We measured occupancy as the number of birds that occupied 60-m grid cells that covered two 18-ha study sites over the 12-year period and similarly calculated rates of reproductive success within each grid cell. Rates of reproductive success were generally high (>60%) and were not correlated with occupancy rates. Return rates also were high, and birds rarely moved far from their first territory (mean = 68 m) during their lifetimes. There was no relationship between site fidelity and past reproductive success, but shift distances decreased with age. Our results differed from past studies that found a relationship between breeding dispersal and past reproductive success for species in a number of habitats. High territory fidelity regardless of past reproductive performance may represent a general case for songbirds breeding in homogeneous, high-quality habitats in which sources of failure are infrequent and unpredictable. In such cases, the potential benefit of moving may not outweigh the costs, and being able to obtain and maintain a territory may be of prime importance. © The American Ornithologists' Union, 2011.


Rexer-Huber K.,P.O. Box 598 | Bildstein K.L.,Acopian Center for Conservation Learning
Polar Biology | Year: 2013

Striated caracaras occur only on the Falkland Islands and the outer islands of southern Chile and Argentina. In summer, the species associates with seabirds and seals and depends heavily upon them for food. The winter diet is less well understood. We studied the diet of 90-130 mainly juvenile and sub-adult striated caracaras overwintering at a farm on Saunders Island, Falkland Islands, in mid-winter (July-August) 2011. Direct observations of feeding and regurgitation pellets collected at a roost indicate that the winter diet of the striated caracaras at the site is mainly native geese, beetles and other invertebrates, and the carcasses of domestic sheep. This study illustrates seasonal shifts in the diet of this near-threatened South Atlantic endemic and suggests an important nutritional link between juvenile and subadult caracara survival in winter and traditional human activities at sheep farms. © 2012 Springer-Verlag Berlin Heidelberg.


Naveda-Rodriguez A.,Acopian Center for Conservation Learning
Journal of Raptor Research | Year: 2015

I here evaluate the conservation status of 64 species of diurnal raptors in Venezuela based on extent of occurrence (EOO) and area of occupancy (AOO) derived from geomatic-based geographic distribution modeling and gap analysis. I modeled the geographic distribution of raptor species to quantify distribution areas using the maximum entropy modeling techniques with nine environmental variables that were believed to influence the geographic distribution of raptors. The EOO and AOO were used to reevaluate the conservation status of diurnal raptors in Venezuela, applying Criteria B of the IUCN Red List. Furthermore, a gap analysis was performed to evaluate the effectiveness of strictly protected areas (SPA) in the conservation of birds of prey. EOO ranged from 10,423 km2 to 907,223 km2 and AOO values ranged from 6566 km2 to 903,193 km2; four species met the B1 criterion and are qualified to be reclassified. The gap analysis revealed that, on average, 20% and 24% of species' EOO and AOO, respectively, were protected within SPA. In theory, SPA are assuming an effective role in the protection of species' geographic distribution. Raptor conservation in Venezuela must be thoroughly planned; an update in land-use planning (territorial ordering) to enhance the connectivity among SPA would improve the protection of raptors. © 2015 The Raptor Research Foundation, Inc.

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