Impact of red-bellied squirrels on the bird community of the Pampas Region, Argentina

Abstract

Ecología Austral, 25:37-45 (2015)

The red-bellied tree squirrel Callosciurus erythraeus was introduced in Luján, Argentina, in 1970, where it spread rapidly. Squirrels can affect birds through nest predation, interference and competition for food and nesting sites. We aimed to compare community composition, density and richness of birds in forested areas within and outside the range distribution (680 km² in 2004) of the main population of these squirrels in the country. We selected seven paired sites (each pair had similar vegetation structure and composition) and other 14 sites, half in each condition (with and without squirrels). In each of these 28 sites, we did 4–5 point counts in each site during spring-summer 2008-2009, recording all bird individuals that were seen/heard <10–20 m from the observer. Species richness was rarefied to the smallest number of point counts per site. Community composition differed among sites with and without squirrels, particularly for paired sites. We found no differences in bird density though species richness was higher for paired sites without squirrels. To assess if squirrels do consume bird eggs and if they have any egg-size preference, we conducted cafeteria experiments offering fruit and three eggs of different sizes to individual squirrels kept in a large cage (3x2x2 m) for < 24 h. Few squirrels (2/25) consumed the eggs. Our results suggest that squirrels could negatively affect some bird species but not through nest predation.