by Lisa Bate
There’s an easy answer to the question: how many toes does an American Three-toed Woodpecker (Picoides dorsalis) have? They have three! So why give this birds such an obvious name? It turns out that having three toes in the woodpecker world is unusual; most woodpeckers have four toes. The only other woodpecker in North America to have three toes is the closely related Black-backed Woodpecker (Picoides arcticus), with two toes facing forward and one backwards. All other woodpeckers have four toes with two facing forward and two facing back.
Another claim to fame for the American Three-toed Woodpecker (Three-toed Woodpecker) is that they have the northern-most range of any woodpecker species in North America, extending into the boreal forests and taiga across Alaska and Canada up to tree limit. Their counterpart, P. tridactylus, has this same claim to fame in Eurasia. Three-toed Woodpeckers in North America range south into New Mexico and Arizona, following the Rocky Mountains, and down to Oregon in the southern Cascades and the Blue Mountains. Isolated populations also occur in the Black Hills of South Dakota. In eastern North America, their range extends down into the Adirondacks.
Three-toed Woodpeckers are a medium-sized (20 cm [8 in]), black-and-white woodpecker. The head is mostly black with a white line behind the eye and white-mustache stripe. They have mainly black upper parts, except in the center of the back, where you will see variable amounts of white. Even from a distance, this is the easiest way to distinguish this species from the Black-backed Woodpecker, which has a solid black back. Three-toed Woodpeckers have a white throat, breast, and belly and heavily barred with black on flanks and sides. The male can be identified by its yellow crown. In juveniles, both sexes may have yellow crowns, but it is minimized in the females. Their scientific name Picoides comes from the Latin word Picus meaning “woodpecker” and the Greek word -oides meaning “resembling”. Dorsalis refers to the ‘back’ where they have white.
Three-toed Woodpeckers are found in mature, or old-growth forests with high densities of snags and dying trees containing insects. They are strongly associated with spruce forests, or pine forests with an aspen component. They are year-round residents, with some exhibiting only small migrations to lower elevations in the winter. They also exhibit irruptive tendencies, with large numbers migrating and congregating in areas recently disturbed by fire, floods, or drought where trees die and attract insects. Numbers of Three-toed Woodpeckers are greatest in forests with high densities of beetle-killed trees and in moderately burned forests where trees retain their bark. They are a species of least concern given their extensive range, but are negatively affected by timber harvesting and forest fragmentation in localized areas due to loss of nesting substrates and reduced food availability.
Three-toed Woodpeckers are primary cavity-nesters, meaning they are capable of excavating a cavity with their chisel-like beaks in a snag or tree for nesting. They are also a keystone species. A keystone species is one that makes up only a small number of the animals in an area, but whose presence allows for the presence of many other animals. After they finish using the nest cavity for breeding, the cavity becomes available to other species incapable of excavating a cavity, like swallows and bluebirds. These non-excavators are called secondary cavity-nesters.
Three-toed Woodpeckers nest in snags, or live trees, containing heart rot. Heart rot does not kill live trees, but slowly decays the heartwood softening it and making it easier for the bird to excavate. The fungi responsible for heart rot, does not affect the sapwood, leaving a hard shell around the nest cavity. This protects the breeding birds from weather and predators. On average, Three-toed Woodpeckers nest about 5 m (16 ft) above the ground. The diameter-at-breast height of nest trees average about 25 to 30 cm (10 to 12 in). In Montana, they typically lay four eggs in May, with young fledging late June to mid-July.
Three-toed Woodpeckers are uncommon and quiet, difficult to detect, but April is a good month to start listening for their drumming. It is the start of the breeding season, and they drum, more than they vocalize, to defend their territories and attract a mate. The drumming pattern of Three-toed and Black-backed Woodpeckers is distinct, which makes them much easier to locate in the forest. Unlike the Hairy Woodpecker, a close relative, whose drum pattern is steady and fast, the drum of the Three-toed Woodpecker is slower and more variable (https://www.allaboutbirds.org/guide/American_Three-toed_Wodpecker/id). Their call is a flat ‘pik’ or ‘pwick’, and their rattle call is far less emphatic than the Hairy’s call, and somewhat reminiscent of a swimmer jumping off a diving board. During the non-breeding season, the best way to locate Three-toed Woodpeckers is while they forage. Listen for pecking, or tapping sounds as they scale off bark to look for insects, larvae, and arthropods. Scaling refers to removing the bark with their beaks.
The foraging method used by Three-toed Woodpeckers offers a biological control, both directly and indirectly, for many insects considered forest ‘pests’. Their primary prey are bark beetles (Scolytidae)—spruce and mountain pine—and their succulent larvae. They obtain their food directly by scaling, flaking, or pecking off the bark to reach the cambium where the beetles build their galleries to lay eggs. Indirectly, woodpeckers can alter the microclimate of the beetle galleries by scaling off the protective cover of bark. This exposes the overwintering larvae to more weather extremes and can help reduce the number of beetles surviving until spring.
You must be logged in to post a comment.