Numerical and behavioural response of Black-headed Gull Chroicocephalus ridibundus on population growth of the expansive Caspian Gull Larus cachinnans

Piotr Skórka,Joanna D Wójcik,Magdalena Lenda,Rafał Martyka

doi:10.1007/s10336-012-0824-4

Abstract

AbstractWe monitored population size from 1996 to 2003 and studied behavioural interactions (in 2001) between the native Black-headed GullChroicocephalus ridibundusand an expansive, opportunistic predator, the Caspian GullLarus 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 Black-headed 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 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.

Highlights

Predation is a process of major importance in biology, influencing the distribution, abundance, and behaviour of most of animals (Lima and Dill 1990; Lima 1998; Cervencl et al 2011; Cresswell 2011)
We examined interactions between the Black-headed Gull Chroicocephalus ridibundus (BHG), a waterbird that is native to Central Europe, and the expansive large-bodied Caspian Gull (CG)
We found that the BHG population size decreased, while the population size of CG increased (r = -0.912, P = 0.003, n = 6 years) until 2001, when the flooding of the reservoir with additional water began (Fig. 2)

Summary

Introduction

Predation is a process of major importance in biology, influencing the distribution, abundance, and behaviour of most of animals (Lima and Dill 1990; Lima 1998; Cervencl et al 2011; Cresswell 2011). The interactions between invasive or expansive species and native ones often constitute a completely new evolutionary situation for two, or more, species that have never coevolved and are confronted with each other over a short period of time (Mooney and Cleland 2001). This may cause the very rapid evolution of both invasive predators and native species (Huey et al 2000; Phillips and Shine 2006; Suarez and Tsutsui 2008). When the expansive or invasive species are both competitors and opportunistic predators, they may have a dramatic effect on ecosystems, since the wide range of native species is potential prey (Mooney and Cleland 2001; Finney et al 2003; Rehage et al 2005; Caut et al 2008; Newson et al 2010)

Methods

Results

Conclusion