Provisioning of mates and chicks by Cayenne and Royal Terns: resource partitioning in northern Patagonia, Argentina
Alejandro J. Gatto A C and Pablo Yorio A BA Centro Nacional Patagónico, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Boulevard Brown 2915, U9120ACV, Puerto Madryn, Chubut, Argentina.
B Wildlife Conservation Society, Virrey del Pino 2632, P 19, Dpto. B, Ciudad de Buenos Aires, Argentina. Email: yorio@cenpat.edu.ar
C Corresponding author. Email: alegatto@cenpat.edu.ar
Emu 109(1) 49-55 https://doi.org/10.1071/MU08025
Submitted: 14 May 2008 Accepted: 28 November 2008 Published: 5 March 2009
Abstract
Cayenne (Thalasseus sandvicensis eurygnathus) and Royal Terns (Thalasseus maximus) breed in mixed colonies in Argentina. This paper presents the first detailed information on their breeding diet and assesses differences and overlap between species in the type and size of prey. During 2004 and 2005, observations of prey delivered to mates and chicks were carried out at Punta León, Patagonia. The diet of Cayenne and Royal Terns comprised nine and 10 prey species respectively. Fish comprised >99% of the prey of both species of tern in the two study years. Both species had a fairly specialised diet based on pelagic schooling fish, mostly Argentine Anchovy (Engraulis anchoita) and two species of silversides (Odontesthes spp.). Despite observed overlap in trophic resources, our results showed that Argentine Anchovy was the main prey for Royal Terns, whereas the two species of silversides together with Anchovy comprised the bulk of the diet for Cayenne Terns. Fish delivered by Cayenne Terns were significantly smaller than those by Royal Terns. Results suggested that both type and size of prey may be important factors permitting food partitioning between the two species of tern during the breeding season.
Additional keywords: Argentine Anchovy, chick-feeding, food-partitioning, mate-feeding.
Acknowledgements
Research was supported by the Wildlife Conservation Society, The Waterbird Society 2005 Nisbet Research Grant, and Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). We thank Germán García, Luján Villanueva Gomila, Walter Svagelj, Nora Lisnizer, Sergio Sanz and Julio Rúa for field assistance; Bernabé Urrutia and people from Estancias ‘El Pedral’ and ‘Bahía Cracker’ for logistical support; Kees Hulsman and Flavio Quintana for helpful advice during field work; and Leo Venerus, Martín García Azorey, and Walter Svagelj for advice with model analyses. Atila Gosztonyi helped in the determination of fish prey species. We thank Organismo Provincial de Turismo of Chubut for the permits to work at Punta León Reserve. Binoculars used in 2005 were provided by Optics for the Tropics. We thank the North American Ornithological Societies Travel Award, Aluar and Fundación Patagonia Natural for support.
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