Feeding and Breeding of Crested Terns at a Tropical Locality — Comparison With Sympatric Black-naped Terns

Abstract

In tropical waters of the northern Great Barrier Reef, Australia, Crested Terns fed their young with prey from seven families of fish and the Order Decapoda; the majority was from the Family Clupeidae (herrings). This diet overlapped with that of the sympatric Black-naped Tern. Both species caught fish from four families in common, including pomacentrids that were a major prey item for Blacknaped Terns. Crested Terns fed their young larger prey-than Black-naped Terns and tended to feed further offshore, although their feeding ranges overlapped considerably. In each breeding season studied, laying by Crested Terns occurred after Black-naped Terns had finished. It is hypothesised that by feeding on smaller prey than Crested Terns, Black-naped Terns can reach breeding condition faster on smaller fish spawned early in the breeding season. Crested Terns may take longer to reach breeding condition feeding on small fish available early in the season or may delay breeding until fish spawned earlier in the summer season have grown to a suitable size. Crested Terns laid their eggs over short periods of not more than 27 days. This brief period at Eagle Island is shorter than that recorded at any other locality on the Australian coastline. Laying at Eagle Island was considerably more synchronous than for the whole of the central to northern region of the Great Barrier Reef. It is hypothesised that food pulses providing the resource necessary to permit breeding are brief at Eagle Island.