Extended Post-Fledging Parental Care in the Red-Tailed Tropicbird and Sooty Tern

Abstract

In an extensive literature search on post-fledging parental care in seabirds, Burger (1980) noted little evidence for the phenomenon in Red-billed and White-tailed tropicbirds (Phaethon aethereus and P. lepturus). On the basis of Fleet's (1974) observations of the Red-tailed Tropicbird (P. rubricauda), she concluded that parents feed their chicks up to 30 days after fledging, but that during this period young remain in the vicinity of the nest. The evidence heretofore available suggests that once young tropicbirds leave the colony, they are independent (see also Nelson 1983). Among terns, extended parental care hundreds of kilometers from nesting colonies has been noted for a number of species (reviewed by Burger 1980). Before now, however, there was little evidence that Sooty Terns (Sterna fuscata) care for fledged young anywhere other than in the colony. Evidence that they might do otherwise is confined to two observations of parent-chick groups 8 and 20 km from Bird Island in the Seychelles (Feare 1975). In this paper we report behaviors that indicate extended post-fledging parental care in Red-tailed Tropicbirds and Sooty Terns. Observations were made during seven cruises across the central and southern Pacific Ocean. The cruises were as follows: (1) from Panama City, Panama, to Wellington, New Zealand, 10 to 30 November 1976; (2) from Long Beach, California, to Wellington (via Tahiti), 15 November to 9 December 1977; (3) from Sydney, Australia, to Long Beach (via American Samoa), 13 March to 5 April 1979; (4) from Ushuaia, Argentina, to Long Beach (via Lima, Peru), 19 April to 28 May 1980; (5) from Seattle to the Equator, 90*W to 160*W, and return, 7 October to 5 December 1983; (6) from Miami to the same section of the Equator (via the Panama Canal) to Honolulu, Hawaii and then to Tahiti, 9 April to 4 June 1984; and, (7) Miami to Honolulu (same route), 9 October to 5 November 1984. Seabirds were censused 30 min each daylight hour that our ships were underway, or between 13 and 15 census periods per day (for details, see Ainley and Boekelheide 1983).