Breeding Population of Streaked Shearwaters(Calonectris leucomelas) and the Effect of Norway Rat(Rattus norvegicus) Predation on Sasudo Island.

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  • 韓国 Sasudo 島におけるオオミズナギドリ(<i>Calonectris leucomelas</i>)の繁殖数とドブネズミ(<i>Rattus norvegicus</i>)による捕食

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Abstract

To estimate the breeding population of Streaked Shearwaters (Calonectris leucomelas) on Sasudo Island, Jejudo, Korea, quadrat surveys were conducted during the hatching period in 1998, the early rearing period in 1999 and the early incubation period in 2000. In 2000, burrow density was 0.15/m2±0.02 (mean±SE). Burrow density was high in the abandoned field, rocky area and take off site of the birds in the island, where 71.3% of 595 burrows were occupied. The breeding population was estimated to be 7, 486±3, 000 pairs (mean±SE). Only 36.4% and 19.8% of burrows were occupied in 1998 (n=353) and 1999 (n=140), respectively. Burrow occupancy seemed to decrease through the breeding stages. Breeding failures were recorded in 31 out of 54 burrows (57.4%) in 7-29 August 1999. Predation by Norway Rats (Rattus norvegicus) was possibly the cause of mortality of eggs or chicks in 26 of these 31 unsuccessful burrows. Norway Rat predation may be the main factor affecting the breeding success of Streaked Shearwaters on the island.

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