Foraging Ecology and Use of Drumming Trees by Three-Toed Woodpeckers

Abstract

Among boreal forest bird species, the three-toed woodpecker (Picoides tridactylus) is closely associated with old-growth forests (>120 years), and possibly the most negatively affected by long-term changes induced by commercial forestry in eastern Canada. Part of this conflict is related to the woodpecker's use of standing dead trees as nesting sites. Moreover, this woodpecker's foraging behavior and its choice of feeding and drumming substrates may increase its vulnerability in managed forests. We describe foraging behavior of three-toed woodpeckers, and characterize foraging and drumming trees used by this species in Quebec's black spruce (Picea mariana) forests. During summer (May-Jul) and mid-winter (Jan-Feb), birds of both sexes used a highly specialized feeding technique consistent with searching for bark beetles (Coleoptera: Scolytidae). Snags were highly preferred over live trees as foraging substrates. Snags used for foraging had a greater diameter at breast height (dbh) and were less deteriorated than paired nearest available snags. When live trees were selected for foraging, they also had a greater dbh but were more deteriorated than nearest available live trees. Thus, only a limited number of trees had all characteristics preferred by foraging woodpeckers, probably as a result of the ecology of its phloem-boring prey. Snags also were highly preferred over live trees as drumming substrates. Drumming snags differed from paired nearest available snags by having a broken top, less bark cover, and a lower deterioration class, which probably provided better acoustic towers for territorial birds. Given the extensive use of snags with different characteristics for foraging and drumming by three-toed woodpeckers, models estimating snag requirements for this species based only on nesting requirements are probably of limited use to maintain populations in managed areas. Wildlife habitat management objectives that specifically require the maintenance and renewal of snags in early decaying stages found in old-growth forests are essential to the conservation of this woodpecker species in managed forests.