New but nice? Do alien sacred ibises Threskiornis aethiopicus stabilize nesting colonies of native spoonbills Platalea leucorodia at Grand-Lieu Lake, France?

Abstract

In spite of the general concerns about introduction of exotic species there are contrary arguments that introduced species could increase local biodiversity and provide ecosystem services. The assertion that native spoonbills Platalea leucorodia are attracted by breeding, introduced sacred ibises Threskiornis aethiopicus, and thus that the spoonbill colonies will be more stable, has been developed as an argument against the proposed eradication of the sacred ibis in western France. We analysed the possible interaction between these two species using information from a 5-year nest survey (2002-2006) in a large swamp in western France. We found that: (1) The spoonbills began to breed significantly earlier than ibises, by 15-25 days. (2) In an analysis using a grid of 80-m squares no site-fidelity effect was observed from one year to the next, both species preferentially using previously unused cells from which the other species was absent and cells occupied by their own species. (3) Spoonbills had a significantly greater dispersion than ibises. (4) The spoonbills almost always settled (90.3%) near a spoonbill nest. These results do not suggest any regular positive attraction of the spoonbills towards the ibises and consequently do not support the proposal that ibises attract spoonbills and play a role in the conservation of this species. © 2010 Fauna & Flora International.