Migration of black‑naped terns in contrasted cyclonic conditions

Authors: Jean‑Baptiste Thiebot, Noboru Nakamura, Yutaka Toguchi, Naoki Tomita, Kiyoaki Ozaki

Year: 2020

Publication: Marine Biology

Publication Link: https://link.springer.com/article/10.1007/s00227-020-03691-0

Abstract: Cyclones are currently increasing in frequency and intensity across the tropical regions, and such changes in cyclonic activity can adversely impact tropical marine ecosystems. To examine the potential effects of these changes on marine migrations, we tracked the annual at-sea distribution of black-naped terns from Okinawa Islands, southwest Japan (26.5° N; 127.9° E). Using light-based geolocation loggers, we compared the migration chronology of six terns between 4 years of contrasted conditions regarding cyclones (regionally called typhoons). Shortly after breeding (30 August ± 13.9 days), the birds undertook their migration across the Philippine Sea to coastal regions of Borneo and Sulawesi Islands, and seemed able to avoid or cross the storm systems. The two birds tracked in years of medium–high typhoon activity (2012–2014) seemed to target a stopover area in the northern Philippines several days after a typhoon hit. By contrast, in 2017, no strong typhoon hit in August and the four study birds showed later departure by 23.8 days, but moved significantly quicker, with little or no stopover. Arrival date at the wintering site was similar among years (1 October ± 3.5 days). Terns thus show remarkable variability in their migration chronology, presumably linked with annual storm frequency. However, the limits to this variability are currently unknown. Further, if individuals respond to environmental cues to time their migration to potentially benefit from lagged
optimal feeding conditions en route, it is likely that the increase of back-to-back cyclonic events in the region may reduce the benefits of such a strategy for surface-feeding predators.

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