Characteristics of foraging habitats and chick food provisioning by tropical Roseate Terns

I studied tropical Roseate Terns (Sterna dougallii) on Aride Island, Seychelles, between 1997-1999. Productivity in 1998 was 0.58 fledglings/breeding pair, and in 1999 no young fledged. Roseate Terns on Aride concentrated their foraging along the coastline exposed to prevailing winds, with flock size over this area being significantly correlated with amount of food offered to chicks. In 1998, Lesser Noddies (Anous tenuirostris) were present in 91% of the Roseate Tern flocks, but in 1999 occurred in only 32%. During the 1998 successful breeding season, Roseate Terns were associated with dense flocks of Lesser Noddies over predatory fish, whereas during the 1999 failure season most Roseate Tern hocks were either monospecific or mixed with Fairy Terns (Gygis alba), and without predatory fish. The mean flock size of Roseate Terns (82 vs. 6 birds) and the rate of foraging attempts (8.3 vs. 2.8 attempts min(-1)) were significantly greater in association with predatory fish. Mullidae (Parupeneus or Mulloidichthys) were the primary prey taken by Roseate Terns, and alternative sources of food were apparently scarce. The high daily variations in the amount of food brought to chicks, intermediate periods of low food delivery, and an apparent seasonal decline in the amount of food brought to the colony suggest that food is unpredictable on a daily and seasonal basis. Absence of predatory fish may explain complete breeding failures and periods of low food delivery, but the importance of other factors is unknown. Information on the ecology and movement patterns of predatory fish around Aride Island is needed to assist the conservation of the Roseate Terns.

I am indebted to James Cadbury of the Royal Society for Nature Conservation, U.K., for permission to conduct research on Aride and for financial assistance to travel there. Norman Ratcliffe of the Royal Society for the Protection of Birds, U.K., helped in preparing the trip to Aride. The help, friendship, and suggestions of the wardens of Aride in 1997, Mike Betts and Susan Barclay, and 1998, John Bowler and Janet Hunter, are gratefully acknowledged. Tony Gill of the Natural History Museum (London) identified the mullids, and Chris Feare helped with suggestions and discussions. The friendship of the island wardens, island staff, and volunteers contributed to a good island-life on Aride. Earlier drafts benefited from the comments of David Shealer, Lisa Ballance, Chris Feare, and Luis Monteiro. Finally, I thank my wife for her continuing patience, understandinga, nd regular phone calls to Aride.