Annual Variation in Breeding Numbers of Two Gull Species in Response to Regional Stock Size and Local Availability of Japanese Sand Lance on Rishiri Island, Northern Japan

Kentaro Kazama; Masahiko Sato; Kazuki Kosugi

doi:10.2326/osj.15.85

Abstract

Breeding population abundance such as colony size of seabirds is not generally considered to be particularly sensitive to the annual dynamics of the food conditions because of the long life-span and high adult survival rate. However, in seabird species in which adults decide to breed or not depending on the food conditions, population abundance can respond sensitively to the annual variation in the food conditions. Here, we examine the effects of the regional annual stock abundance of Japanese Sand Lance Ammodytes personatus, and their local temporal availability during the egg-laying period on the size of a Black-tailed Gull Larus crassirostris and Slaty-backed Gull L. schistisagus, breeding colony over 12 years on Rishiri Island, northern Japan. The total number of nests of both gull species increased significantly with the regional annual stock abundance, but not with the local temporal availability of the sand lance. The number of Black-tailed Gull nests without eggs was significantly higher in the year with lower local temporal availability indicating that more Black-tailed Gull parents gave up egg-laying after nest building. Colony size in these species can be a useful indicator reflecting local food conditions.

DOI: http://dx.doi.org/10.2326/osj.15.85

Received 10 4月 2015 Accepted 27 6月 2015

Acknowledgments:

We thank N. Sugimura, R. Murayama, R. Sato, S. Okada, Y. Maeda, Y. Osa, T. Yamamoto, T. Nishijima, K. Hirata, H. Fujii, H. Takahara, M. Arikushi, S. Miyamoto, Y. Watanuki, N. Takahashi, J. Kaji, K. Nakaya, T. Kawabata, and M.T. Kazama for their support and assistance in the field. We also thank M Shirai for supporting analyses of the fish catching data. We would also like to thank Y. Niizuma and two anonymous reviewers for their critical and constructive comments for our manuscript, and Mark Brazil, Scientific Editing Services, for assistance in the preparation of the final draft of the manuscript. Counts of Black-tailed Gulls nests during 2001, 2002 and 2003 were conducted as a population census program of Hokkaido Soya sub-prefectural office and Northern Hokkaido branch of Wild Bird Society of Japan. Hokkaido Soya sub-prefectural office gave us permission to work on the Black-tailed Gulls on Rishiri Island after 2004. This work was supported by JSPS Grants-in-Aid for Scientific Research (#26840151) and for JSPS Fellows (#13J05174).

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