Merlin

Williamson's Sapsucker Life History

Habitat

Habitat Forests

Williamson’s Sapsuckers nest in the coniferous and mixed conifer-deciduous forests of mountainous western North America, from the Rockies westward. They inhabit mostly higher elevations, especially drier forests with western larch, Douglas-fir, white fir, grand fir, red fir, Engelmann spruce, ponderosa pine, lodgepole pine, Jeffrey pine, mountain hemlock, water birch, and trembling aspen. They tend to nest in relatively open woodlands and below ridgelines. They are not known to nest in moist forests with western redcedar or western hemlock, though migrants and wintering birds use many different sorts of habitats, including oak scrub, pinyon pine-juniper, and riparian corridors. Females winter at lower elevations than males and appear to use more diverse habitats than males.

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Food

Food Insects

Williamson’s Sapsuckers feed heavily on the sap of coniferous trees, as well as on the phloem (the moist inner bark tissue that conducts sap). To harvest the sap, they drill rings of shallow holes called sapwells around trees. They eat these substances year-round but very heavily in spring, as sap rises and they prepare to raise young. Most pairs maintain wells in 4–6 trees when nesting, and they may use the same trees for many consecutive years. Williamson’s makes sapwells in conifers, not in deciduous trees. As young hatch, this species begins to feed heavily on ants as well as beetles, aphids, flies, and other insects. They take ants mostly by picking them from live trees and branches, at all heights in trees, and occasionally from the ground. They hop methodically along a trunk or branch, capturing the ants, which often travel single file to tend colonies of aphids in trees. On rare occasions, Williamson’s Sapsuckers may catch an insect in flight. In winter, they include fruit and seeds in the diet, with madrone, juniper, pinyon pine, and various berries recorded. Insect prey includes carpenter ants, wood ants, velvet tree ants, black ants, mountain pine beetle, click beetles, lady beetles, rove beetles, ground beetles, longhorned beetles, checkered beetles, scarab beetles, aphids, crane flies, moths (and larvae, such as western spruce budworm). They occasionally eat arachnids such as spiders or false scorpions. Like other sapsucker species, they sometimes eat insects or other prey caught in sap at the sapwell and occasionally expose insects beneath bark by flaking, scaling, or drilling, but most of their foraging involves gleaning insects from bark and occasionally from foliage.

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Nesting

Nest Placement

Nest Cavity

Male and female select a live tree (often one with a fungal infection that softens the heartwood) to excavate a nest hole, usually in a larger, older tree.

Nest Description

Nest holes average about 1.6 inches in diameter; the nest cavity averages about 3.6 inches across and 10.5 inches deep. Wood chips line the bottom of the cavity.

Nesting Facts
Egg Description:

Glossy white.

Condition at Hatching:

Naked, eyes closed, helpless.

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Behavior

Behavior Bark Forager

Male Williamson’s Sapsuckers begin to establish territories before females arrive on the breeding grounds. Courtship usually involves the male making a bounding flight on fluttering wings toward the female, perching beside her, and swinging the head side to side while giving staccato calls. Males are very territorial at this time of year, chasing away other males of their species (and sometimes other woodpeckers) that enter the territory, which is usually 10 acres or larger. Rival males sometimes also engage in physical combat. Male and female share incubation and brooding duties, and both feed the nestlings. Both sexes take naps (often longer than an hour) while clinging to a tree; males also nap in the nest cavity with the young. Both sexes chase away birds that come too near a nest with nestlings inside. Pairs part company after young have fledged and may re-mate in subsequent seasons or change partners. On occasion, Williamson’s Sapsuckers that have just finished a breeding cycle commence courtship displays, prospect for nest sites, and excavate a new nest with a different partner but do not actually breed. At night, wintering Williamson’s Sapsuckers roost in natural or excavated cavities. During the day, they frequently sunbathe, spreading the wings to increase exposure. They tolerate others of their species on the wintering grounds and so probably do not maintain wintering territories.

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Conservation

Conservation Low Concern

According to the North American Breeding Bird Survey, Williamson's Sapsucker populations were roughly stable between 1968 and 2015. Partners in Flight estimates a global breeding population of 300,000 and rates the species a 12 out of 20 on the Continental Concern Score, indicating a species of low conservation concern. In Canada, the species is listed as Endangered because of habitat loss of mature western larch. Local declines in Williamson’s Sapsuckers may be owing to loss of more mature forests, where they nest at their highest densities. The species avoids most extensively logged forests. They don’t use recently burned forests immediately after a forest fire, but they do use these habitats beginning about a decade after the fire.

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Credits

Gyug, Les W., R. C. Dobbs, Thomas E. Martin and Courtney J. Conway. (2012). Williamson's Sapsucker (Sphyrapicus thyroideus), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Partners in Flight (2017). Avian Conservation Assessment Database. 2017.

Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link (2017). The North American Breeding Bird Survey, Results and Analysis 1966–2015. Version 2.07.2017. USGS Patuxent Wildlife Research Center, Laurel, MD, USA.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, USA.

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