OBSERVATIONS ON THE MARINE DISTRIBUTION OF TROPICBIRDS SOOTY AND BRIDLED TERNS, AND GADFLY PETRELS FROM THE EASTERN INDIAN OCEAN

WA Museum Records and Supplements | Updated 1 decade ago

Abstract: Observations of pelagic birds were made in the eastern Indian Ocean during a cruise on R. V. Franklin during October 1987. The Christmas Island form of the White-tailed Tropic bird Phaethon lepturus fulvus was observed up to 1300 km ESE of their breeding station, in water close to the shelf edge. White·tailed Tropic birds generally occupied water masses of lower salinity than Red-tailed Tropic birds Phaethon rubricauda and, as a consequence, the two species were not recorded in close proximity. Both species foraged solitarily. The relatively high salinities in the marine habitat of P. rubricauda may explain its penetration of the sub-tropics as a breeding species. A short-lived breeding episode at Rottnest Island apparently followed a period of relatively low sea surface salinity, approaching the range recorded for this species at sea. Such oceanographic events, associated with the strength of the Leeuwin Current, may underly the range extension of P. rubricauda into south-western Australia.

Observations of Bulweria bulwerii, Pterodroma baraui and P. rostrata recorded during the cruise suggest that these gadfly petrels are seasonal visitors to the tropical, eastern Indian Ocean.

Sooty Terns Sterna fuscata did not occupy water masses where the sea surface temperature was much below 23°C and apparently preferred active warm current areas, such as the South Equatorial Current. Bridled Terns S. anaethetus frequented the higher salinity waters which occur across the continental shelf over a wide latitudinal range.