Numerical and behavioural response of Black-headed Gull Chroicocephalus ridibundus on population growth of the expansive
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ORIGINAL ARTICLE
Numerical and behavioural response of Black-headed Gull Chroicocephalus ridibundus on population growth of the expansive Caspian Gull Larus cachinnans Piotr Sko´rka • Joanna D. Wo´jcik • Rafał Martyka Magdalena Lenda
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Received: 6 July 2011 / Revised: 2 January 2012 / Accepted: 30 January 2012 / Published online: 17 February 2012 Ó The Author(s) 2012. This article is published with open access at Springerlink.com
Abstract We monitored population size from 1996 to 2003 and studied behavioural interactions (in 2001) between the native Black-headed Gull Chroicocephalus ridibundus and an expansive, opportunistic predator, the Caspian Gull Larus cachinnans, at water reservoirs in Poland. The expansive species caused a population decline in the native species and affected its choice of nest sites. The Black-headed Gulls perceived the risk of predation on the part of the larger Caspian Gulls. When both species occurred in close proximity, the native gull breeding pairs built nests where the vegetation was higher and its cover greater than at the sites chosen by pairs breeding far away from the expansive species. The native gulls in proximity to the expansive species spent more time guarding their nests. However, this was not compensatory, as egg losses were higher and breeding success much lower in pairs breeding near the Caspian Gulls than in those breeding far from the latter. Such a low breeding performance in the Blackheaded Gulls was probably caused either by predation on the part of Caspian Gulls or by aggressive interactions among Black-headed Gulls. In fact, the rate of intraspecific
Communicated by P. H. Becker. P. Sko´rka (&) Institute of Environmental Sciences, Jagiellonian University, Gronostajowa 7, 30-387 Krako´w, Poland e-mail: [email protected] J. D. Wo´jcik Institute of Systematics and Evolution of Animals, Polish Academy of Sciences, Sławkowska 17, 31-016 Krako´w, Poland R. Martyka M. Lenda Institute of Nature Conservation, Polish Academy of Sciences, Mickiewicza 33, 31-120 Krako´w, Poland
aggression in native gulls was higher in pairs breeding in proximity to the expansive species than in those breeding far away from it. These intraspecific fights, caused by the presence of the expansive species were, at least partially, responsible for egg and chick losses. We did not find the presence of native gulls to have any effect on the behaviour and breeding performance of the expansive gull. These results indicate that the expansive predatory Caspian Gull negatively affects local population size and alters the behaviour of the native Black-headed Gull, and may, both directly and indirectly, affect its reproductive performance. Keywords Behaviour Breeding success Range expansion Invasion Nest-site selection Zusammenfassung Auswirkungen des Populationswachstums der expansiven Weißkopfmo¨we Larus cachinnans auf Populationsgro¨ße und Verhalten der Lachmo¨we Chroicocephalus ridibundus Wir haben die Populationsgro¨ße der Lachmo¨we Chroicocephalus ridibundus an polnischen Stauseen
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