The predator-prey size hypothesis in three assemblages of forest birds.

I investigated morphological pattern and preysize preference of three bird assemblages (14 species altogether) in a Hungarian oak forest, during the breeding seasons of 1979-1986. To assess the occurrence of competition for food among forest birds I performed a 5-year removal experiment with two hole-nesting passerines, the great tit and the blue tit. Prey preference of both species was affected by the presence of the other species. The results of both the removal experiment and the estimation of available food supply indicated food limitation, at least for foliage-gleaning birds. However, I found neither a regular size ratio among species nor a strong relationship between predator size and prey size. Other phenomena such as foraging strategies may affect preysize preference. Therefore, a competition model including only morphological ratios and predator-prey size relationships is too simplified.