Species Composition, Timing, and Weather Correlates of Autumn Open-Water Crossings By Raptors Migrating Along the East-Asian Oceanic Flyway

Camille B. Concepcion; Patricia T. Dumandan; Medel R. Silvosa; Keith L. Bildstein; Todd E. Katzner

doi:10.3356/JRR-16-00001.1

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1 March 2017 Species Composition, Timing, and Weather Correlates of Autumn Open-Water Crossings By Raptors Migrating Along the East-Asian Oceanic Flyway

Camille B. Concepcion, Patricia T. Dumandan, Medel R. Silvosa, Keith L. Bildstein, Todd E. Katzner

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J. of Raptor Research, 51(1):25-37 (2017). https://doi.org/10.3356/JRR-16-00001.1

Abstract

Raptor migration rarely involves long-distance movements across open oceans. One exception occurs along the East-Asian Oceanic Flyway. We collected migration data at two terrestrial hawkwatch sites along this flyway to better understand open-ocean movements along this largely overwater corridor. At the northern end of the Philippines, at Basco on the island of Batan, we recorded 7587 migratory raptors in autumn 2014. Near the southern end of the Philippines, at Cape San Agustin on the island of Mindanao, we recorded 27,399 raptors migrating in autumn 2012. Chinese Sparrowhawks (Accipiter soloensis) were the most common raptors observed, making up approximately 89% and 92% of total records for Basco and Cape San Agustin, respectively. The Grey-faced Buzzard (Butastur indicus) was the second most common raptor migrant, accounting for 8% of the total counts at both watch sites. The migration period was about 1–2 wk earlier at Basco, the more northerly site, than at Cape San Agustin. Overwater flights at Basco peaked in both the morning and late afternoon, whereas at Cape San Agustin there was only a morning peak. In general, the rate of migration passage at both sites was highest with clear skies when winds were blowing from the northwest. However, we observed interspecific differences in migration behavior at both sites, with Accipiters more likely to be observed with tailwinds and eastward winds, and Grey-faced Buzzards more likely observed with headwinds. These results help to characterize poorly known aspects of raptor biology and to identify potential migratory bottlenecks or key sites for raptor conservation in little-studied Philippine tropical ecosystems.

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Camille B. Concepcion, Patricia T. Dumandan, Medel R. Silvosa, Keith L. Bildstein and Todd E. Katzner "Species Composition, Timing, and Weather Correlates of Autumn Open-Water Crossings By Raptors Migrating Along the East-Asian Oceanic Flyway," Journal of Raptor Research 51(1), (1 March 2017). https://doi.org/10.3356/JRR-16-00001.1

Received: 4 January 2016; Accepted: 1 August 2016; Published: 1 March 2017

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