Trophic resource partitioning among terns in different species coexisting contexts: an integrated classical and isotopic niche approach

GATTO, ALEJANDRO; YORIO, PABLO

Conferencia; 1st World Seabird Conference; 2010

The trophic ecology of South American (Sterna hirundinacea), Cayenne (Thalasseus sandvicensiseurygnathus) and Royal (Thalasseus maximus) terns was evaluated at the colonies of Punta Leòn (43°S) and Punta Loma (42°S), Patagonia, Argentina. Cayenne terns bred with the larger Royal terns in the former and with the smaller South American terns in the latter. The diet and use of marine areas were evaluated by means of prey delivery observation, radiotelemetry and stable isotope analysis. Data were then compared and integrated to evaluate the potential differencesin their use of trophic resources. At each colony, the larger tern species showed a higher prey specialization, included a larger proportion of the prey with higher energetic content (Engraulis anchoita), and showed a higher trophic level than the smaller one. The larger tern species in both colonies preyed upon larger fish than the smaller one. Telemetry data suggest that tern species have a similar use of foraging areas, but differ in their temporal foraging patterns. Royal and Cayenne terns at Punta Leòn showed higher amplitude in the isotopic niche in relation to the trophic level of their prey, but a relatively low amplitude in the use of the marine space. In contrast, Cayenne and South American terns at Punta Loma showed higher amplitude in the use of the marine space and relatively low amplitude in relation to prey trophic level. Results suggest that tern species differ in their trophic resource utilization, and that differences are dependent on the combination of coexisting tern species.