Kees Hulsman

The robbing behaviour of terns and gulls

The robbing behaviour of some larids at One Tree Island, Great Barrier Reef, was observed. Terns usually were moderately successful when robbing members of their own species but stole only a few fish brought into a colony. Between species, Roseate Terns rarely succeeded though they often tried to rob Black-naped Terns whereas Silver Gulls frequently succeeded and often tried to rob Lesser Crested and Crested Terns. The number of attempts by most species was greatest during high tide when the most pirates were round the colonies. The success of Silver Gulls varied in time and place. Some of the variables that affected the success were the number of Gulls attacking a tern, the length of the fish, the size of the pirate relative to its victim and the strategy used.

Breeding success and mortality of terns at one tree island, great barrier reef

Defence of the nest by Black-naped, Roseate, Lesser Crested and Crested Terns and strategies of predation used by Silver Gulls were studied. Strategies used by Gulls differed as did the rate of success between individuals and only a few were responsible for most predation. Their behaviour was affected by the size of the defender of the eggs or chicks and by the size of an egg. Breeding success and causes of mortality of eggs and chicks of Black-naped, Roseate, Bridled and Crested Terns were determined. Mortality resulted mainly from predation (1.6 to 83.1%), flooding of nesting areas (6.6 to 50.6%) and starvation (< 82.4%) caused by a cyclone preventing adults foraging for at least three days. However, the importance of these causes of mortality differed among colonies over three successive breeding seasons. Although the breeding success of Lesser Crested Terns was determined, the main causes of mortality were not. The generalizations that populations are limited by abundance of food or competition for it are discussed. Breeding success of Black-naped and Roseate Terns is too low to maintain the present size of their colonies at One Tree Island. In contrast, the colonies of the Bridled and Crested Terns can be maintained or possibly increased, depending on post-fledging mortality.

Biology and Growth of the Black-naped Tern Sterna Sumatrana: An Hypothesis to Explain the Relative Growth Rates of Inshore, Offshore and Pelagic Feeders

The Black-naped Tern breeds on tropical and sub-tropical islands throughout the Indian and Western Pacific Oceans. In Australian waters they are non-sedentary. They usually breed during spring and summer. The mean clutch size is about 1.5 and it is incubated for 21 to 23 days. Most Black-naped Terns hunt within two kilometres of their colonies. Young are fed often; the modal interval between feedings was four to five minutes and the mean was 49.6 minutes. They ate fish from at least 15 families and up to 10 cm long. The mean size of prey fed to chicks increased during the course of the breeding season. Nestlings were fed a greater number of small fish than were chicks (> 7 days old) and mates. The size of fish fed to chicks and mates did not differ significantly but the ones eaten by foraging adults differed significantly from those that they fed to their mates. Breeding success of Black-naped Terns was higher at Eagle Island than at One Tree Island. The major causes of mortality of eggs and chicks were predation by gulls and flooding of nesting areas. Growth rates of Black- naped chicks (inshore feeder) were faster than those of offshore and pelagic feeders. We hypothesise that the ability of parents to transport food to their young (Ricklefs power requirements model) in combination with the nutrient composition of their diets explain the non-genetic differences in the growth rates of inshore, offshore and pelagic feeders. We postulate that inshore feeders provision their young with more of the limiting nutrient per unit time by supplying their young with more food than is reauired to meet their enerev needs. Ricklefs model also accounts for the changes in.the use of foraging zones during the cburse of the breeding season.

Breeding numbers and population trends of Wedge-tailed Shearwater (Puffinus pacificus) and Black Noddy (Anous minutus) in the Capricornia Cays, southern Great Barrier Reef

Abstract Wedge-tailed Shearwaters and Black Noddies are the two numerically dominant seabird species found in the southern section of the Great Barrier Reef, Australia. This research provides baseline breeding population estimates for nine of 16 islands in the Capricornia Group over five years for Shearwaters (1996–2000) and four years for Noddies (1997–2000). With estimates of ∼302000 active breeding pairs of Black Noddies and ∼560000 breeding pairs of Wedge-tailed Shearwaters in the area, the research results have confirmed the importance of the Capricornia Group as a recognised breeding area for these birds.