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6 April 2019 Topographic drivers of flight altitude over large spatial and temporal scales
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Bird movements vary spatially and temporally, but the primary drivers that explain such variation can be difficult to identify. For example, it is well known that the availability of updraft influences soaring flight and that topography interacts with weather to produce these updrafts. However, the influences of topography on flight are not well understood. We determined how topographic characteristics influenced flight altitude above ground level (AGL) of a large soaring bird, the Golden Eagle (Aquila chrysaetos), over several regions within the State of California, USA. Primary drivers of flight AGL, those to which eagles showed the same response at all spatial scales, were topographic roughness, ground elevation and the east-west component of aspect (eastness). Each of these is related to formation of thermal updrafts. Secondary drivers, those to which eagles showed region-specific patterns, included topographic position, percent slope, and the north-south component of aspect (northness). In contrast to primary drivers, these secondary drivers were related to formation of both thermal and orographic updrafts. Overall, drivers of flight altitudes that were related to thermal updrafts showed different levels of complexity due to spatial and temporal variation of those drivers than did flight altitudes related to orographic updrafts.

Published by Oxford University Press for the American Ornithological Society 2019. This work is written by (a) US Government employee(s) and is in the public domain in the US.
Adam E. Duerr, Tricia A. Miller, Leah Dunn, Douglas A. Bell, Peter H. Bloom, Robert N. Fisher, Jeffrey A. Tracey, and Todd E. Katzner "Topographic drivers of flight altitude over large spatial and temporal scales," The Auk 136(2), 1-11, (6 April 2019).
Received: 27 August 2018; Accepted: 2 January 2019; Published: 6 April 2019

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