Trophic interactions during chick rearing between Kelp Gulls and Cayenne and Royal terns

MARINAO, C.; SUÁREZ, N.; YORIO, P.

Puerto Iguazú

Congreso; Ornithological Congress of the Americas (XVII RAO/XXIV CBO/XCV AFO); 2017

Association of Field Ornithologists, Sociedade Brasileira de Ornitologia y Aves Argentinas

Terns are one of the most affected groups by gulls, through predation,kleptoparasitism and competition for nesting sites. These interactions havebeen reported in Patagonia, where Cayenne and Royal terns (Thalasseussandvicensis eurygnathus and T. maximus, respectively)nest in mixed-species colonies with the Kelp Gull (Larus dominicanus).However, trophic interactions between these species have not been yetevaluated. During 2014, we assessed their diet during the chick stage at theBahía San Blas Protected area, through the analysis of Kelp gull chick stomachsamples (n=66) and direct observation of prey deliveries (DO) in Cayenne andRoyal terns (n=1747 and 1014, respectively), in addition to stable isotopeanalysis (SIA) of chick whole blood (n=10 per species). Engraulis anchoita wasthe main prey shared by the three species. In both tern species, this was oneof the three most frequent prey (~30% DO; ~ 50% SIA), together with twosilverside species, while in the Kelp Gull it showed a frequency of ~35% (bothmethods) followed in similar frequencies by Cynoscion guatucupa derivedfrom recreational fishery waste. Both analysis indicated that the overlapbetween the trophic niches of Kelp Gulls and each tern species was low(Czekanowski Index<0,20, in both cases; SEAc<10%, in both cases). Thetrophic overlap does not seem to be relevant, but the interaction between thesespecies should be assessed particularly in scenarios where anthropogenicresources are not available for the Kelp Gull.