The Impact Of Timing On Breeding Success In Red-footed Booby, Xisha Archipelago

Red-footed Booby (Sula sula) is a widely distributed pelagic seabird. It may have several laying peaks throughout the year, and their breeding cycle approximately to one year. The tropic seabird living in an indistinctive seasonal marine environment, and the mechanism that control the timing of breeding in tropic sea was not clear at present. This study was conducted on Xisha Archipelago, which located in the north South China Sea. The weather in Xisha Archipelago is tropical monsoon-type climate. The basic study was carried in 2003-2004, and a detailed study from September 2006 to May 2008 was conducted to investigate the relationship between timing of breeding, reproductive success and local environment.The breeding seasons of 2006/2008 was divided into three periods, they were early period (from August to September), middle period (November to December), and late period (March to April). The breeding seasons of 2003/2006 were approximated from the end of September to early April next year. The timing of each period had great variance in two breeding seasons while the length of each seasons were consistence approximately.The reproductive success of 2006/2007 season was 20.9% (n = 148) and the highest (57.4%) occurred at late period. The reproductive success of 2007/2008 season was 17.9% (n = 117) and the highest (28.9%) occurred at late period. Reconstruction of nests could improve the productivity of breeding pairs. The occurrence of typhoon could drastically affect the reproductive success. The older young and the longer span from typhoon date to mean nesting date had higher survival probability when encounter the same typhoon.From 1973 to 2008, most typhoons occurred at June– October in Xisha Archipelago. It suggested that the distribution pattern of typhoon is the main reason for shaping the heaviest nesting peak in December in 2002/2006 seasons. However, the Utor changed the normal breeding time and formed the heaviest nesting peak in late period.From 13 July 2007 to 10 December 2007, two peaks of food abundance out of three were correlated with breeding time; it suggested that food may be a major cause of reproductive activities. Meanwhile, Squid took more part in food proportion also correlated with the breeding time. It suggested that the changing of Squid availability may be the basic reason that causing a cascade effect.