Low seasonal variation in the diet of Rock Shags (Phalacrocorax magellanicus) at a Patagonian colony in Argentina
Alexandra Sapoznikow A C , Flavio Quintana A B and Luisa Kuba AA Centro Nacional Patagónico (Conicet), Boulevard Brown 3600 (9120), Puerto Madryn, Chubut, Argentina.
B Wildlife Conservation Society, 2300 Southern Boulevard, Bronx, NY 10460, USA.
C Corresponding author. Present address: Paso 348, 9120, Puerto Madryn, Chubut, Argentina. Email: alexamadryn@yahoo.com.ar
Emu 109(1) 35-39 https://doi.org/10.1071/MU07061
Submitted: 13 October 2007 Accepted: 27 October 2007 Published: 23 February 2009
Abstract
The characteristics of the food sources exploited by seabirds are one of the main factors determining the abundance and distribution of those birds. Determination of the diet over the year and between breeding and non-breeding seasons is important in understanding the food sources and their potential relationship with seabird population dynamics. We studied seasonality in the diet of the Rock Shag (Phalacrocorax magellanicus), a seabird endemic to southern Argentina and Chile, at a colony at Punta Loma, Chubut, by analysis of pellets (regurgitated casts) collected weekly during two consecutive non-breeding and breeding seasons in 2002 and 2003. We identified 19 prey-types in the diet. Polychaetes were the most common item, being present in 80–90% of the samples. Fish were also dominant in both non-breeding and breeding seasons (present in 60–80% of the pellets), especially species of Patagonotothen, Ribeiroclinus and Helcogrammoides. Crustaceans and cephalopods were also present in the diet, but to a lesser extent. There was a high overlap in dietary composition between non-breeding and breeding seasons, although more crustaceans and cephalopods were consumed during the non-breeding season in 2002. Results indicate that the food sources of Rock Shags are present in their feeding areas throughout the year, although many of these species are restricted in their availability, are of small size and have low energy content.
Additional keywords: Cormorants, foraging ecology.
Acknowledgements
We thank Wildlife Conservation Society, Consejo Nacional de Investigaciones Científicas y Técnicas (Conicet), and Agencia Nacional de Promoción Científica y Tecnológica for funding this study. A. Sapoznikow received a doctoral fellowship from Conicet. We are grateful to E. Zárate, A. Fortini, C. Serrago, E. Berrier, M. Deamo, F. Marquez, Y. Idaszkin, L. Agüero, R. Palacio, S. Copello, A. Gatto, M. Torres, S. Finochiaro, N. Lisnizer, M. Keller, M. A. Díaz, J. Rua, R. Vera and Ecocentro Puerto Madryn for their help during field work. G. Lana, A. Jiménez, D. Jindra, A. Lezcano and F. Marquez installed the nets to collect the pellets. Y. Idaszkin, M. Keller and F. Perez helped us to analyse the samples collected. Lobo Orenzans, Atila Gosztonyi and Catalina Pastor helped to identify prey-items. David Galvan help us to learn about ANOSIM and SIMPER analysis. We specially thank the hospitality of the rangers of Reserva Provincial Punta Loma; Organismo Provincial de Turismo and Dirección Provincial de Fauna Silvestre of Chubut for the permits to work at Punta Loma Reserve; and Centro Nacional Patagónico for institutional support. Rory Wilson provided helpful comments on the manuscript. Finally, we would like to thank three anonymous reviewers whose comments improved the final version of this paper.
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