Food choice and feeding by male and female Common Treecreepers (Certhia familiaris) during the nestling period

Abstrakti

Decreased intensity of interspecific competition may be expected to lead to increased variation within the population, especially in the form of sexual dimorphism . As the Common Treecreeper is the only species belonging to the so-called trunk-foraging guild in the coniferous study area in Central Finland, apart from the more strongly billed woodpeckers, its foraging behaviour and/or sites could be expected to differ between the sexes. Moreover, the sexual dimorphism in this species is considerable . About 99% of the food items used by the Common Treecreepers were arthropods . Aphids were the most frequent, but spiders were most important by weight (65%). This pattern did not change with the nestling age. Taxonomically the nestling food was diverse. The average food load contained 14 .2 items (24.2 mg) and did not differ between the sexes. The number of food items per load decreased with increasing mean prey weight. The content of the load differed slightly between the sexes. Load weight increased with the age of the nestling in females, but not in males. These results suggest that the sexes may differ in their foraging sites.