Exploitation competition between hole-nesters (Muscardinus avellanarius, Mammalia and Parus caeruleus, Aves) in Mediterranean woodlands


*Maurizio Sarà. E-mail: mausar@unipa.it


Data from a long-term study (1993–2003) using artificial nest-boxes, were analysed to examine competition for nesting between blue tit Parus caeruleus and common dormouse Muscardinus avellanarius in Sicily. Occupation rates and the reproductive biology of the blue tit in sample woodlots outside the distribution area of the common dormouse were used as a control in sample areas where the two species were syntopic. A selection test showed that the two species, when living in syntopy, actively chose the small nest-boxes, thus overlapping in the use of the same spatial resource. The experimental exclusion of the common dormouse from nest-boxes caused an increase of blue tit occupation rate. Once the effect of nest-box density was removed, complementary density changes between the two species clearly appeared. The population cycle of both species in the areas of syntopy showed a swinging pattern, i.e. in areas or during years of common dormouse high abundance few blue tits bred and vice versa. The abundance of the blue tit was affected not only by common dormouse abundance, but also by some habitat and climate variables. Blue tits had low breeding success and a high percentage of nest failure (38% in syntopy vs 3% in control areas), owing to nest destruction and predation by common dormouse, as well as probably also by other rodents (23%) and Martes martes (15%). Another experiment, using stuffed models, showed that the blue tit recognized the common dormouse as an enemy, and behaved as if confronted by a competitor or predator species to protect their nests.