Food diversity and niche-overlap of sympatric tits (Great Tit, Parus major, Blue Tit, Cyanistes caeruleus and Coal Tit Periparus ater) in the Hyrcanian Plain Forests

This study was carried out between early summer 1998 and late summer 1999 in the Hyrcanian Plain forests, the southern Caspian Sea woodlands. In total, the gizzard contents of 241 specimens of the Great Tit (Parus major Linnaeus, 1758), Blue Tit (Cyanistes caeruleus Linnacus, 1758), and Coal Tit (Periparus ater (Linnaeus, 1758)) were collected so that the percentages of grit, plants and animal materials could be estimated and the plant and invertebrate species consumed identified. The data were tested by a series of Mann-Whitney U, ANOVA and Kruskal-Wallis tests. To survey niche overlap of food materials between species and season, the symmetrical overlap index developed by PIANKA (1973) was used. The most important invertebrates (maximum of percentage per season) in the diet of P. major were Coleoptera (36.5%) and Lepidoptera (33.6%), for C. caeruleus Coleoptera (34.5%) and Araneae (3 1.2%), and for Pe. ater Coleoptera (38.2%) and Araneae (35.6%). The most important plants consumed by P. major were Sorghum halepense (68.7%) and Ficus carica (65.6%), by C. caeruleus were F. carica (67.5%) and Alnus glutinosa (39.4%), and by Pe. ater were Lonicera spp. (82.9%). There was a greater degree of overlap and competition for animal food, but plant feeding overlap among the three tit species was low. Two species, P. major and C caeruleus, showed high feeding overlap for animal items (0.92), whereas Pe. afer and C. caeruleus had no significant feeding overlap. The Coal Tit had a greater tendency to forage for vegetable matter and P. maior had a greater tendency to forage for animal matter. Analysis of gizzard contents of P. major and Pe. ater showed that, despite the high degree of feeding overlap, the extent of plant materials consumed indicated no significant competition between the two species. Because Pe. ater is present mostly in autumn and winter, this study cannot establish any degree of competition and food-niche overlap during the breeding season between this and other tit species.