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RESEARCH ARTICLE
Contents Vol 107(4)

Comparative habitat use by syntopic Kelp Gulls (Larus dominicanus) and Olrog’s Gulls (L. atlanticus) in coastal Patagonia

Pablo García-Borboroglu A B C and Pablo Yorio A B
+ Author Affiliations
- Author Affiliations

A Centro Nacional Patagónico, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Boulevard Brown 3600, (9120) Puerto Madryn, Chubut, Argentina.

B Wildlife Conservation Society, 2300 Southern Boulevard, Bronx, New York, NY 10460, USA.

C Corresponding author. Email: pgborbor@cenpat.edu.ar

Emu 107(4) 321-326 https://doi.org/10.1071/MU07021
Submitted: 11 April 2007  Accepted: 5 November 2007   Published: 7 December 2007

Abstract

We studied comparative microhabitat use by breeding Kelp Gull (Larus dominicanus) and the threatened Olrog’s Gull (Larus atlanticus) at six colonies through the distributional range of Olrog’s Gull in coastal Patagonia, Argentina. The ranges of values for most of the 13 microhabitat variables measured (related to vegetation, soil and topography) were broader for the Kelp Gull than Olrog’s Gull, with those of that latter within the range of Kelp Gull, indicating potential spatial conflict between the two species. There was particular overlap in nest-site characteristics, but differences were observed between the two species. Multivariate analyses showed that the most important differences in habitat between the two species related to vegetation cover and distance to the high-tide line. Compared with Kelp Gulls, Olrog’s Gulls placed their nests in sites with lower proportion of vegetation cover, lower percentages of silt–clay in the substrate, and closer to the high-tide line. For both species the patterns of nest-site selection did not vary among colonies, although the extent of differences between the two species varied with availability of habitat at each colony. Although Olrog’s Gulls started laying 12–14 days earlier than the larger Kelp Gulls, the latter occupied breeding colonies earlier and may, therefore, interfere with settlement of Olrog’s Gulls. Considering the increase in the numbers, colony area and nesting density of Kelp Gulls currently observed in coastal Patagonia, there is an urgent need to implement monitoring programs for both species and conduct studies to better predict the results of their interactions.

Additional keywords: habitat overlap, nest selection, spatial conflicts.


Acknowledgements

Research was funded by grants from the Wildlife Conservation Society, Consejo Nacional de Investigaciones Científicas y Técnicas, and Agencia de Promoción Científica y Tecnológica. We thank Centro Nacional Patagónico (CONICET) for institutional support and Soriano SA, Prefectura Naval Argentina, and the Munic. de Punta Alta for logistical support. The Chubut, Río Negro, and Buenos Aires Provincial governments permitted us to work in areas under their jurisdiction through provincial laws No. 3257, 1960 and 11723, respectively. J. Moreno, J. Potti, and L. Reyes provided field assistance and helpful comments on the manuscript. We thank J. Owen, R. Vera, M. A. Díaz, F. Garay, G. Soria, J. P. Rubinich, and L. Musmeci for field assistance. P. G. B. is grateful to Dr Luc Hoffmann for continuous support to his work.


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