COS 3-5 - CANCELLED - Is my neighbor a friend or competitor: a foraging strategy of Black-tailed gull (Larus crassirostris) based on a temporal-spatial gradient.

Abstract: Species sharing the same food resource segregate foraging sites and time strategically to avoid harsh competition and maximize fitness. Adequate foraging strategies are essential for seabirds in a breeding season since foraging success directly impacts offspring and individual survival. The foraging strategies may also be altered based on temporal gradients such as rearing period or fledging, post-breeding, etc., or spatial gradients such as breeding colonies population, distance from major foraging sites, etc. Although foraging strategies for the breeding season is well studied so far, there is still limited information about the strategies for post-breeding which is also a crucial season for an individual to repair itself from reproduction and survive the harsh wintering environment. The study aims to find out the strategy transition of the post-breeding season for long-lived seabirds and how this strategy differs by spatial conditions. Black-tailed gull (Larus crassirostris; BTG) breeding on an island on all side of the Korean peninsula is a generalist as well as opportunist which optimize its foraging strategies by altering food resource from fishery by-product to even urban trash. The breeding condition of islands can be largely categorized by the sea the islands are located in: Yellow Sea, East Sea, and South Sea. Islands in the Yellow Sea, usually highly clustered, are very close to the mudflat as well as rise field and fishery spots. Because there are lots of foraging sites, islands are mostly highly populated with BTG as well as other seabirds. Opposite to the Yellow Sea, the East Sea has the opposite characteristics, and the South Sea has a middle feature. We compared a foraging strategy of six breeding colonies (three from the Yellow Sea, two from the East Sea, and one from the South Sea) with 92 BTG’s during the post-breeding season. The foraging strategy was compared with the Maximum foraging distance, Foraging efficiency for a breeding period and Maximum dispersal distance, Average distance dispersal per day, First-day foraging efficiency. As a result, individuals breeding in the East Sea foraged short distances with high efficiency in the breeding period but distance drastically increased when they are foraging for self-repair or preparing for the wintering. Individuals breed in the Yellow Sea foraged long distances with low efficiency during the breeding period with large variation by breeding colonies. This may be a result of the energy balance between foraging availability and the energy balance of flying distance and competition.