American Three-toed Woodpecker Picoides dorsalis Scientific name definitions

The American Three-toed Woodpecker (Picoides dorsalis), formerly known as the Three-toed or Northern Three-toed Woodpecker, is now considered distinct from populations in the northern Palearctic, where the Eurasian Three-toed Woodpecker (Picoides tridactylus) occurs. The American Three-toed Woodpecker is similar to other North American Picoides in having a heavy, chisel-like bill. Closely related to the Black-backed Woodpecker (P. arcticus), both species have comparable facial markings and differ from other North American woodpeckers in having 3 versus 4 toes and an absence of red in all plumages. The distribution of the American Three-toed Woodpecker generally coincides with that of spruce (Picea) forests, and thus, it breeds farther north than any other woodpecker species in North America. Like the Black-backed Woodpecker, and to a lesser degree the Hairy Woodpecker (P. villosus), the American Three-toed Woodpecker may benefit from locally abundant insect outbreaks resulting from natural disturbances such as wildfires and windthrow. The American Three-toed Woodpecker, however, forages mostly by scaling the bark of trees in search for bark beetles (Scolytidae), while the Black-backed Woodpecker excavates deeper into the wood in search of wood-boring beetle larvae (Cerambycidae). Populations of both woodpecker species are irruptive, but these irruptions are not necessarily simultaneous, which may reflect differences in their food preferences.

This resident of boreal coniferous forest has been little studied, owing to its quiet nature and therefore low detectability during passive surveys. It is generally uncommon, and unlike the Black-backed Woodpecker, the American Three-toed Woodpecker does not exhibit high population fluctuations following forest disturbances created by insect outbreaks. These characteristics, combined with its remote northern distribution, make it difficult to determine reliable population trends. The strong association of the American Three-toed Woodpecker to mature and old-growth spruce forests or recently disturbed forest stands make the species vulnerable to habitat loss and fragmentation that results from modern forestry. Indeed, short-rotation logging, fire suppression, and salvage logging of trees damaged by fire or insect outbreaks reduce the abundance of the species’ favored prey in both early-successional and late-successional forest stands.

Increased awareness of the importance of natural disturbances in forest ecosystems and economic pressure to expand logging in old-growth boreal forest has heightened interest in this woodpecker species. Still, the paucity of life-history data makes the American Three-toed Woodpecker an ideal candidate for further study. Among the most important research needs is to clearly define its ecological niche in areas where it is sympatric with the Black-backed Woodpecker. Other important ecological questions include: (1) long-term impacts of timber harvesting and salvage logging on its populations, (2) dynamics of dispersal and other demographic rates, (3) spatial and temporal pattern of pulse-resource interactions on demography, (4) wintering ecology, and (5) impacts of projected climate change.