Matthieu Le Corre

Breeding seasons of seabirds at Europa Island (southern Mozambique Channel) in relation to seasonal changes in the marine environment

Tropical seabirds have evolved a wide range of breeding regimes to fit with their local environment. The western Indian Ocean shows various oceanic situations, providing opportunities to link variations in breeding phenology with variations of the environment. The breeding seasons of seabirds at Europa Island (Mozambique Channel, western Indian Ocean) are analysed. Three oceanic, tuna-associated species (the sooty tern Sterna fuscata , the red-footed booby Sula sula , and Audubons shearwater Puffinus lherminieri ) breed during austral winter (June–October), whereas the red-tailed tropicbird Phaethon rubricauda breeds during austral summer (November–April). During winter, sea-surface temperatures are the lowest, subtropical waters are the closest to the island, and long-line catches of tunas are important. Thermal fronts occur during winter, in relation to the northward shift of subtropical waters. This is known to be favourable to tunas, and I suggest that the winter breeding of sooty terns, red-footed boobies and Audubons shearwaters is because of an increase in the abundance of tunas. Geographic variations in the breeding phenology of sooty terns in the western Indian Ocean largely support the hypothesis that sooty terns take advantage of cool subtropical waters, when those waters are within their foraging range. The red-tailed tropicbird is a solitary forager, not associated with tunas. During the chick-rearing period, 40% of the mass of food brought to the chicks consists of dolphin-fishes Coryphaena spp. Those warm water, surface dwelling fishes are known to migrate in relation to sea-surface temperatures. Seasonal changes in the occurrence or vulnerability of dolphin-fish in the Mozambique Channel may have favoured a summer breeding regime in red-tailed tropicbirds at Europa Island. Further studies of the marine life of seabirds are needed to test these hypotheses and to learn more about the foraging ecology of tropical seabirds.

THE BREEDING SEABIRDS OF TROMELIN ISLAND (WESTERN INDIAN OCEAN): POPULATION SIZES, TRENDS AND BREEDING PHENOLOGY

Summary Le Corre, M. 1996. The breeding seabirds of Tromelin Island (western Indian Ocean): population sizes, trends and breeding phenology. Ostrich 67: 155–159. Formerly six or eight species of seabirds bred on Tromelin Island, but currently only two species do so: The Redfooted Booby Sula sula and the Masked Booby S. dactylatra. The last two species which became locally extinct, the Lesser Frigatebird Fregata ariel and the Greater Frigatebird F. minor, probably stopped breeding on the island as a consequence of human disturbance to breeding colonies. The populations of the two species of booby have opposing trends since 1954. The Masked Boobys population increased from 60 pairs in 1954 to 200–250 pairs in 1996 while the Red-footed Boobys population decreased from 500 pairs in 1968 to 130–180 pairs in 1996. The impacts of human settlement, introduced brown rats Rattus norvegicus, local extinction of the Greater Frigatebird and other factors are discussed to explain these changes in population sizes. Ne...

Breeding habitat and conservation priorities in Pterodroma baraui, an endangered gadfly petrel of the Mascarene archipelago

The endemic Baraus petrel (Pterodroma baraui) is restricted to the island of La Reunion in the Mascarene archipelago where it breeds on the upper slopes of the highest mountains in areas that are virtually inaccessible to humans. Although the species is considered to be critically endangered, little is known about its biology and the actual threats for Baraus petrel on its breeding grounds have never been investigated. In this paper we report data that were collected during the first ever visit of a Baraus petrel colony. The species breeds underground in upland elfin forests between 2400 and 2700 m above sea level. A thick, undisturbed, humus layer appears to be a prerequisite to burrow establishment, which implies that the species may be especially susceptible to trampling by humans or other large vertebrates. We found evidence of past exploitation of Baraus petrel by humans. In addition, the colony is inhabited by three, possibly four, species of introduced commensals, including Rattus sp., which imposes predation on eggs and chicks and may affect the breeding success. We stress the need to establish control campaigns to eradicate potential predators from the nesting colonies and long-term monitoring projects for the Baraus petrel before it undergoes irreversible population decline.