Body size, prey handling efficiency and choice of diet in three coniferous forest tits (Paridae)

The main purpose of this study was to link morphological differences between great tit ( Parus major ), willow tit ( P. montanus ) and coal tit ( P. ater ) and their rate of energy acquisition and choice of diet in order to explore the potential for competitive relations between them more directly. Handling times were measured in the laboratory by presenting mealworms of different sizes to the birds. Great tits were more efficient in handling large prey than were the smaller-bodied willow- and coal tits; for small prey sizes the coal tit was the least efficient species. Using the ratio of prey mass to the handling time value, a utility function for each species was constructed. These results suggests a potential for a segregation of the species on the food axis. However, results from the prey choice experiment show that despite considerable differences in functional morphology between the three species they do not differ significantly in the range of prey size exploited. My results suggest that the alleged importance of prey size partitioning is not likely to play the major role for the coexistence of these coniferous forests tits.