COMPARATIVE DIETS OF ADULT AND YOUNG THREE-TOED WOODPECKERS IN A EUROPEAN ALPINE FOREST COMMUNITY

Abstract

We studied year-round food preferences of the three-toed woodpecker (Picoides tridactylus) from 1994 to 2000 in Berchtesgaden National Park, Germany. We color-banded 52 birds for individual recognition, and we radiomarked 25 adults from this sample. We analyzed 142 feces of 30 adults and 588 feces of 40 nestlings from 15 nests. Additionally, we took samples from 20 trees recently used for foraging in 10 woodpecker territories to estimate local prey availability. Based on relative abundance and relative frequency of food items (i.e., importance value), overall diet composition of adult three-toed woodpeckers was dominated by spiders (Araneidea), larvae of longhorn beetles (Coleoptera, Cerambycidae), and bark beetles (Coleoptera, Scolytidae). Adults ate longhorn beetle larvae primarily during nesting, while imagines (fully developed adults) and larvae of various bark beetles appeared to be the main food resource outside the nesting season. Nestling diet was dominated by spiders and longhorn beetle larvae that were gathered 247 ± 122 m (x̄ ± SD) from the nest. Our results demonstrated that consumption of bark beetles by three-toed woodpeckers varies throughout the year, being lowest during the nesting season, while longhorn beetle larvae are preferred throughout the year. Securing habitat requirements of both bark and wood-boring beetle communities is a critical step to maintaining viable three-toed woodpecker populations.