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Somerset, PA, United States

Katzner T.E.,West Virginia University | Katzner T.E.,U.S. Department of Agriculture | Katzner T.E.,U.S. Geological Survey | Turk P.J.,Colorado State University | And 6 more authors.
Journal of the Royal Society Interface

Large birds regularly use updrafts to subsidize flight. Although most research on soaring bird flight has focused on use of thermal updrafts, there is evidence suggesting that many species are likely to use multiple modes of subsidy. We tested the degree to which a large soaring species uses multiple modes of subsidy to provide insights into the decision-making that underlies flight behaviour. We statistically classified more than 22 000 global positioning satellite-global system for mobile communications telemetry points collected at 30-s intervals to identify the type of subsidized flight used by 32 migrating golden eagles during spring in eastern North America. Eagles used subsidized flight on 87% of their journey. They spent 41.9%±1.5 (x¯ ±s.e.m., range: 18-56%) of their subsidized northbound migration using thermal soaring, 45.2%±2.1 (12-65%) of time gliding between thermals, and 12.9%±2.2 (1-55%) of time using orographic updrafts. Golden eagles responded to the variable local-scale meteorological events they encountered by switching flight behaviour to take advantage of multiple modes of subsidy. Orographic soaring occurred more frequently in morning and evening, earlier in the migration season, andwhen crosswinds andtail windswere greatest.Switching between flight modes allowed migration for relatively longer periods each day and frequent switching behaviour has implications for a better understanding of avian flight behaviour and of the evolution of use of subsidy in flight. © 2015 The Author(s) Published by the Royal Society. All rights reserved. Source

Duerr A.E.,West Virginia University | Miller T.A.,West Virginia University | Lanzone M.,Cellular Tracking Technologies LLC | Brandes D.,Lafayette College | And 7 more authors.
Functional Ecology

Animals respond to a variety of environmental cues, including weather conditions, when migrating. Understanding the relationship between weather and migration behaviour is vital to assessing time- and energy limitations of soaring birds. Different soaring modes have different efficiencies, are dependent upon different types of subsidized lift and are weather dependent. We collected GPS locations from 47 known-age golden eagles that moved along 83 migration tracks. We paired each location with weather to determine meteorological correlates of migration during spring and fall as birds crossed three distinct ecoregions in north-east North America. Golden eagle migration was associated with weather conditions that promoted thermal development, regardless of season, ecoregion or age. Eagle migration showed age- and season-specific responses to weather conditions that promoted orographic lift. In spring, adult eagles migrated earlier, over fewer days, and under more variable weather conditions than did pre-adults, suggesting that adults were time limited and pre-adults made choices to conserve energy. In fall, we found no difference in the time span of migration or when each age class migrates; however, we saw evidence that pre-adults were less efficient migrants than adults. The decision by soaring birds to migrate when thermals developed allowed individuals to manage trade-offs between migratory speed and migratory efficiency. When time was limited (i.e. spring movement of adults speeding towards nesting territories), use of whatever lift was available decreased the time span of migration. When migration was not time limited (e.g. spring movements by pre-adults, all movements in fall), eagles avoided suboptimal flight conditions by pausing migration, thus increasing the time span of migration while reducing energetic costs. © 2014 British Ecological Society. Source

Duerr A.E.,West Virginia University | Miller T.A.,West Virginia University | Cornell Duerr K.L.,Westminster College, Pennsylvania | Lanzone M.J.,Cellular Tracking Technologies LLC | And 4 more authors.
Biodiversity and Conservation

Anthropogenic development has great potential to affect fragile desert environments. Large-scale development of renewable energy infrastructure is planned for many desert ecosystems. Development plans should account for anthropogenic effects to distributions and abundance of rare or sensitive wildlife; however, baseline data on abundance and distribution of such wildlife are often lacking. We surveyed for predatory birds in the Sonoran and Mojave Deserts of southern California, USA, in an area designated for protection under the “Desert Renewable Energy Conservation Plan”, to determine how these birds are distributed across the landscape and how this distribution is affected by existing development. We developed species-specific models of resight probability to adjust estimates of abundance and density of each individual common species. Second, we developed combined-species models of resight probability for common and rare species so that we could make use of sparse data on the latter. We determined that many common species, such as red-tailed hawks, loggerhead shrikes, and especially common ravens, are associated with human development and likely subsidized by human activity. Species-specific and combined-species models of resight probability performed similarly, although the former model type provided higher quality information. Comparing abundance estimates with past surveys in the Mojave Desert suggests numbers of predatory birds associated with human development have increased while other sensitive species not associated with development have decreased. This approach gave us information beyond what we would have collected by focusing either on common or rare species, thus it provides a low-cost framework for others conducting surveys in similar desert environments outside of California. © 2015, Springer Science+Business Media Dordrecht (out side the USA). Source


Cellular Tracking Technologies LLC | Date: 2014-01-21

Wildlife GPS and data logger devices.

Lanzone M.J.,Cellular Tracking Technologies LLC | Miller T.A.,West Virginia University | Miller T.A.,Pennsylvania State University | Turk P.,West Virginia University | And 8 more authors.
Biology Letters

Soaring birds that undertake long-distance migration should develop strategies to minimize the energetic costs of endurance flight. This is relevant because condition upon completion of migration has direct consequences for fecundity, fitness and thus, demography. Therefore, strong evolutionary pressures are expected for energy minimization tactics linked to weather and topography. Importantly, the minute-by-minute mechanisms birds use to subsidize migration in variable weather are largely unknown, in large part because of the technological limitations in studying detailed long-distance bird flight. Here, we show golden eagle (Aquila chrysaetos) migratory response to changing meteorological conditions as monitored by high-resolution telemetry. In contrast to expectations, responses to meteorological variability were stereotyped across the 10 individuals studied. Eagles reacted to increased wind speed by using more orographic lift and less thermal lift. Concomitantly, as use of thermals decreased, variation in flight speed and altitude also decreased. These results demonstrate how soaring migrant birds can minimize energetic expenditures, they show the context for avian decisions and choices of specific instantaneous flight mechanisms and they have important implications for design of bird-friendly wind energy. © 2011 The Royal Society. Source

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