Spatial and Temporal Foraging Movement Patterns in Royal Terns (Thalasseus maximus) and Cayenne Terns (Thalasseus sandvicensis eurygnathus) in Northern Patagonia, Argentina

Abstract

Royal Terns (Thalasseus maximus) and Cayenne Terns (Thalasseus sandvicensis eurygnathus) breed sympatrically in Patagonia, and very little is known about their breeding foraging patterns. Simultaneous information on the foraging patterns of both species using VHF radio-telemetry is presented from a mixed species colony in the Punta León Protected Area (43° 04ʹ S, 64° 29ʹ W), Chubut, Argentina. Transmitters were deployed on nesting adults of each species, which were tracked during the late incubation period between 21 November and 3 December 2006. In total, 101 locations of foraging terns were identified by means of radio-telemetry from the coast. Royal and Cayenne terns foraged primarily in waters less than 15 km offshore. Attenuation and lack of signal reception in some of these trips indicate that foraging also took place in waters further away, but in most cases along the coastline. Results indicate a different temporal pattern of nest departures between species. Royal Tern departure frequencies were not uniform, peaking around midday. In contrast, Cayenne Tern departure frequencies were higher around morning twilight, with lower peaks during early morning and evening twilight.