BFL: Species Account: Williamson's Sapsucker

WILLIAMSON'S SAPSUCKER

Williamson's Sapsucker (Sphyrapicus thyroideus)

Distribution

Breeding: Southern British Columbia south through central Washington Williamson's Sapsucker range map to central California, also from Idaho and western Montana extending south through Utah, western Wyoming and western Colorado to northwestern New Mexico and northern Arizona.

Winter: Central Arizona and New Mexico south through the Sierra Madres to central Mexico.

Breeding habitat

Throughout range, breeds at middle to high elevations, generally from 4,900–10,500 feet (1,500–3,200 meters), in montane spruce-fir, Douglas fir, lodgepole pine, and ponderosa pine forests, but also in mixed deciduous-coniferous forest with quaking aspen as an important nesting substrate. Nests from 2,800–4,250 feet (850–1,300 meters) in extreme northern portion of range; availability of suitable nests sites (snags) is a critical component of breeding habitat.

Conservation status

This woodpecker is of moderate conservation importance, primarily because of its limited and patchy breeding range, low overall density, and association with mature forests of the western mountains. Being a primary cavity nester, this species provides nest-sites for many other forest species. Populations of this species are poorly monitored, and we have little information on status or trends. Understanding its relationship with forest fragmentation and silvicultural practices will be important for maintaining future populations.

Description

Male: All black upperparts with a large, white wing patch and white rump; chin and throat red, breast black, belly yellow, flanks barred black and white. Head black with narrow white stripes.

Female: Lacks red chin and white wing patch of male; back, wings, and sides are barred with white and brown, rump white. Dark patch on breast, belly variably yellow.

Juvenile: Resemble adults, but coloring is duller.

Vocalizations

Drum: Similar to Red-naped Sapsucker, but slower and more regular, with longer beats. Described as a steady roll of taps followed by single, loud taps at irregular intervals.

Calls: Six different calls:

Churr call: Mainly a male vocalization functioning as territorial announcement or pair formation, often given in association with drumming.

Chatter call: Usually given softly, used as communication between mates, often precopulatory. Varies from slow ch-ch-ch series to rapid bursts.

Ch-hah: Given at the beginning of a territorial or courtship interaction, also used as an alarm call. Consists of two hoarse syllables, the second syllable lower in pitch, less emphatic, and longer in duration.

Rattle call: Used at the end of a territorial or courtship interaction; also used as alarm call. Described as a rapid, guttural trill.

Scold or Alarm call: The most common vocal response to intruders near a nest or sap tree. Consists of a short, sharp, hoarse guttural roll dropping rapidly in pitch.

Scream call: A shrill, high pitched call, often given when a bird is caught and held by humans.

Foraging strategy

Mostly sapsucking and insect-gleaning from tree bark. Concentric rings of shallow wells (holes) are drilled in sap trees, which are checked periodically for sap and trapped insects. Sections of bark may be removed to facilitate greater sap drainage. Occasionally flycatches, flying out from trunks in a small loop to catch insects in midair.

Diet

Omnivorous, exhibiting high seasonal specialization. During the pre-nestling period, feeds exclusively on conifer sap, but shifts to mainly ants after young hatch. Other insects, e.g. beetles, flies, aphids, are also taken during the breeding season.

Behavior and displays

Male defends territory, especially during establishment, often chasing conspecific males.

Intruding males and resident males often drum or exchange churr calls (see "Vocalizations" above) within sight of each other, culminating in retreat of the intruder or aggressiveness by resident male.

Spends most of its time clinging to and climbing vertical surfaces of tree trunks.

Approaches nest containing young by landing above nest hole and descending "jerkily" to level of hole.

Courtship

Pre-copulatory displays include a "bouncing (fluttering) flight" display, where the male approaches his mate from above while giving a chatter call, and descends slowly (fluttering) to perch beside her as both birds call.

After a series of "bobbing-wagging" displays, the male initiates copulation.

Nesting

Nest site: Nests in newly excavated cavities adjacent to open ponderosa forest. Similar to requirements of Red-naped Sapsucker, but Williamson’s tends to select nest sites in areas close to conifer-dominated forest with few aspens, while Red-naped chooses deciduous-dominated (i.e., aspen) areas.

Height: Average height about 8 feet (2.5 meters).

Nest: Males appear to excavate the majority of the cavity, working several hours a day for 3-4 weeks, although females have been observed excavating at least some of the time. Inside the nest cavity, a small bed of wood chips and shavings serve as bed for eggs.

Eggs: 3-7 (usually 4-6) pure white and slightly glossy eggs are laid, one per day.

Incubation period: Incubation begins before clutch is complete, and usually lasts 12-14 days.

Nestling period: Young are altricial, with eyes closed, naked, and bright flesh-pink in color at hatching, and nestling ages differ by 1-2 days; sexually dimorphic plumage patterns appear immediately. Nestlings are capable of weak vocalizations soon after hatching, and beg almost constantly thereafter, becoming increasingly louder with time. Both parents brood young, each parent feeds nestlings, rotating brooding and foraging activity for the first 2 weeks. Unlike most other ant foragers, this species does not regurgitate food to its young; instead, parents carry food, mostly ants, in throat, mouth and bill.

Fledgling period: Nestlings depart the nest cavity 31-32 days after hatching, usually requiring 1-2 days, but often up to 3-4 days, for the entire brood to leave nest. Once fledglings emerge, they do not reenter the cavity, but fly to nearby tree to be fed by parents.

Broods: Single brooded.

Cowbird Parasitism: Not known to occur.

Notes

Williamson’s and Red-naped Sapsuckers have similar nest-site preferences, but may sustain ecological separation by selecting nest sites on basis of proximate foraging habitat.