The Relationship between Vegetation Cover and Hatching Success, and Chicks' Survival in Black-Tailed Gulls on Hongdo Island

ABSTRACT : During the breeding seasons in 2002 and 2003, the influences of vegetation cover on breedingprocesses of Black-tailed Gulls ( Laurs crassirostris ) were studied on Hongdo Island. We checked clutch sizes,calculated hatching success and survival rates on day 15 and a vegetation cover. There was significant positiverelationship between vegetation cover and hatching success, and survival on day 15. In order to analyze therelationship, sample nests were categorized as 'exposed' and 'covered' nests, and the breeding processes ateach nest were compared. Hatching success and survival on day 15 in covered nests were significantly higherthan ones in exposed nests. However, in clutch size, there was no significant difference. The rate of the hatchingand survival failure was different amongst the categorized nests. The primary cause of hatching failure in coveredand exposed nests was 'disappeared', and the primary causes of survival failure on day 15 were 'disappeared'and 'killed by adults'. The failure in exposed nests was significantly larger than that of covered nests. In thebreeding of Black-tailed Gulls on Hongdo Island, vegetation cover influenced the survival of eggs and chicks asthe cover provided shelter against predators and extreme weather.