FORAGING PATTERNS OF THE LEAST TERN (STERNA-ANTILLARUM) IN NORTH-CENTRAL OKLAHOMA

Because the interior least tern (Sterna antillarum) is piscivorous, lo cations of colony sites and reproductive success are strongly influenc ed by distance to bodies of water with available forage. We examined f oraging patterns and success of the least tern nesting on a salt flat in north-central Oklahoma during the 1992 and 1993 breeding seasons. O ur objectives were to 1) estimate whether there were limited quantitie s of forage available to breeding least terns, 2) examine least tern u se of bodies of water adjacent to the salt flat, and 3) identify fish species brought to colony sites and in bodies of water adjacent to the salt flat. Chicks were fed smaller fish than were brooding adults and chicks were offered more fish than they consumed. Adults did not fora ge away from the salt flat during incubation and brooding (peak hatchi ng). Foraging success of terns observed fishing away fr om the salt fl at from May to June was increased by fingerlings available at a fish h atchery approximately 12 km from the salt flat. During incubation, bro oding, and fledging (July), the only location away from the salt flat where terns were observed feeding was the eastern shoreline of the Gre at Salt Plains Reservoir. Collections of fish dropped and left uneaten by least terns in colony sites contained six species. These collectio ns served as an index of species selected by the least tern. The six s pecies of dropped fish were present in all samples seined from adjacen t waterways. Sizes of fish in seine samples and of fish brought to nes ts were smaller than those of fish found dropped and uneaten in colony sites. These uneaten fish ma) have been too big to consume. Quantity and quality of fish available to least terns during our study were ade quate and did not appear to limit reproductive success. Forage availab ility may only be a limiting factor to reproductive success during dro ught years.