Timing and flight mode of departure in migrating European bee-eaters in relation to multi-scale meteorological processes |
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Authors: | Nir Sapir Martin Wikelski Roni Avissar Ran Nathan |
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Institution: | (1) Movement Ecology Laboratory, Department of Evolution, Systematics and Ecology, Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Jerusalem, Israel;(2) Max Planck Institute for Ornithology, Vogelwarte Radolfzell, Radolfzell, Germany;(3) Department of Biology, Konstanz University, Konstanz, Germany;(4) Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL, USA;(5) Department of Integrative Biology, University of California—Berkeley, 3060 Valley Life Sciences Building, Berkeley, CA 94720-3140, USA |
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Abstract: | Understanding departure decisions of migratory birds and the environmental factors affecting them is important for predicting
their distribution, abundance, and arrival times to breeding and wintering areas. In the past, methodological difficulties
to obtain fine-scale bird departure and meteorological data have limited testing the multi-scale effects of meteorology on
bird departure during migration. We investigated departure timing of European bee-eaters (Merops apiaster) staging in southern Israel, identified their departure flight mode (flapping or soaring) using radio telemetry, and measured
local meteorological conditions to study if bird departure was affected by these. Departure timing was examined using a timescale
analysis design. The conditions before, during, and after the time of departure were compared using timescales of 24 h, 6 h,
1 h, and 10 min and in relation to bird flight mode. At the between-days timescale, barometric pressure at departure time
was significantly lower compared with 2–1 day earlier, whereas temperature at departure was significantly higher compared
with 3–2 days earlier. Temperature at departure was also higher compared with 6 h and 3–2 h earlier. Tailwind assistance had
no significant effect at any timescale. Soaring birds departed at significantly higher temperature compared with flapping
birds. We suggest that bee-eater departure is tuned to the infrequent passage of warm atmospheric depressions at the between-days
timescale and with an increasing temperature trend within these days enabling the birds to use energetically cheap soaring
flight. We thus suggest that energetic considerations dictate the departure decisions of migrating European bee-eaters. |
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