Case report: Long-term GPS tracking throughout the breeding and non-breeding seasons of the streaked shearwater Calonectris leucomelas

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The collection of wildlife tracking information throughout a species’ entire life cycle is important for comprehensive ecological elucidation and the establishment of practical protected areas. Although streaked shearwater (SS) is a seabird species for which biologging techniques are highly developed, there have been no reports of successful global positioning system (GPS) tracking during the early breeding and non-breeding seasons, when recapture is difficult. In this study, we succeeded in long-term GPS tracking, obtaining highly accurate tracking data during the non-breeding season from November to March and the early breeding season from April to July. We discuss the relationship between prey distribution and the marine environment to understand the species’ foraging habitat preferences. In September 2018, we attached GPS tags to birds breeding on Toshima, in the Izu Islands, and recaptured two birds in August 2020 and 2022. The tags worked for 277 and 549 days and fixed 23,510 and 37,233 positions, respectively. During the early breeding season, the foraging area had low sea surface temperatures (SST) and high chlorophyll-a (Chl-a) concentrations and moved northward as the season progressed. During the non-breeding season, one bird wintered in the South China Sea and the other off northern New Guinea. In the South China Sea, SS preferred sea areas with an average SST of 26 °C and high Chl-a concentrations (> 0.8mg/m3), whereas off northern New Guinea, SS preferred an area with an average SST of 29 °C. The foraging area used during the early breeding season depended on the optimal water temperature zone for their primary prey—Japanese Anchovy. The foraging areas used during the non-breeding season matched the optimal water temperature zones of the main fish distributed in each sea area. The GPS tracking data obtained in this study, while not a statistically sufficient sample size, are valuable and provide new insights into the environmental preferences of SS during early breeding and non-breeding seasons; life stages for which little information is available.