Mixed clutches of Blue Tits Parus caeruleus and Great Tits Parus major in nest boxes in Central Italy

In hole nesting birds and especially in tits Parus mixed clutches, laid by two or more species in the same nest, are often observed (Merilä 1994). In this paper we report four mixed clutches of Parus caeruleus and P. major in nest boxes in the Presidential Estate of Castelporziano (41°44’N, 12°24'E), where populations of these two species, studied since 1991 (Bellavita & Sorace 1994, Sorace et al. 1994, Petrassi et al. 1997), reach very high density, superior to those in other areas of Central Italy (Bellavita & Sorace 1994).