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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Acknowledgements We would like to thank Reuven Yosef and Tzadok Tzemah from the International Birding and Ringing Center in Eilat (IBRCE) for their hospitality and assistance with bird trapping, Bill Cochran and Itzik Simhayof for their help in constructing the tracking systems, and Ofir Altstein, David Troupin, Adi Ben-Nun, Adena Brickman and members of the Movement Ecology Lab, and tracking teams for their assistance in the field and lab. We would like to thank the Israeli Meteorological Service and especially Amos Porat and the meteorology unit of the Jacob Blaustein Institutes for Desert Research Ben-Gurion University for providing the meteorological data. This work was supported by the US–Israel Binational Science Foundation (grant no. 229/2002 and 124/2004), the Ring Foundation for Environmental Research, and the Robert Szold Fund for Applied Science. N.S. was supported by two Rieger–JNF fellowships and a Fulbright doctoral dissertation travel fellowship.
- Arava Valley
- Atmosphere dynamics
- Bird migration
- Cross-country flight
- Decision rules