Variable success in breeding of the Roseate Tern Sterna dougallii on the northern Great Barrier Reef

Abstract

Breeding of Roseate Terns Sterna dougallii on the northern Great Barrier Reef (11°-15°S) was monitored between 1976 and 1994, and they were recorded breeding on the inshore rocky islands in most years, usually starting April—May. Between 50–5000 pairs were recorded breeding each year and indicate that the northern Great Barrier Reef is an important breeding area for Roseate Terns during peak years when large colonies of 1000–5000 pairs formed on low sand cays in the far northern Great Barrier Reef (11°S). On at least three occasions, breeding success was poor in these large colonies, with high mortality of the almost-fledged chicks. Growth in weight and wing length of Roseate Tern chicks was measured at Eagle Island (14°42'S) between 1983 and 1986 in order to assess the influence of food on growth rates and survival. Chicks took up to 35 days to fledge, significantly longer than the ecologically similar, more numerous Black-naped Tern Sterna Sumatrana at the same site at the same time and also almost 10 days longer than Roseate Tern chicks from temperate North American colonies. These data suggest that conditions in northern Australia are rarely favourable for the rapid growth and breeding success of Roseate Terns. Pelagic fish populations around inshore islands in tropical Australia may only be able to support limited numbers of Roseate Terns during the breeding season. This makes northeastern Australian populations of this globally threatened species extremely vulnerable to changes in the availability of their prey during the breeding season.