FOOD RESOURCE MATCHING BY FORAGING TITS PARUS SPP. DURING SPRING-SUMMER IN A MEDITERRANEAN MIXED FOREST - EVIDENCE FOR AN IDEAL FREE DISTRIBUTION

We analysed whether patterns of microhabitat use by Blue Tits Parus ca eruleus, Great Tits Parus major and Crested Tits Parus cristatus inhab iting a mixed Forest consistently matched the patterns of food availab ility experienced by foraging birds during spring-summer. The use of f ive microhabitats by each bird species (the foliage of three tree spec ies, shrubs and ground) and the availability of food in trees during t he prebreeding, breeding and postbreeding periods of the birds' annual cycle were measured. All three tit species foraged mainly in the oute r part of tree canopies (small branches and leaves or needles), Tit di stributions between tree species matched food resource distributions i rrespective of overall food resource levels, which varied four-fold be tween the study periods, and tit species. Tits also exploited secondar y microhabitats (shrubs and ground) in periods of low food availabilit y; Blue Tits tended to use shrubs, whereas Great and Crested Tits fora ged on the ground. Between-trees distributions fitted that expected fr om an ideal free distribution, suggesting that food availability and i ntraspecific exploitative competition were the main factors governing tree use by tits, In contrast, patterns of use of secondary microhabit ats (shrubs and ground) seemed to indicate a role for the species-spec ific morphological con figurations of each tit species since Blue Tits are better adapted to hang and tended to forage in shubs, whereas Gre at and Crested Tits are better adapted to feed on horizontal surfaces and tended to forage on the ground. No evidence of interspecific inter actions was observed. Overall, the results pointed to an independent e xploitation of Mediterranean mixed forest by each bird species, food a vailability and food accessibility being the main factors affecting mi crohabitat use by foraging tits.