White-headed Woodpecker Dryobates albolarvatus
Version: 2.0 — Published July 9, 2020
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For first-time breeders, pair bonds can be established within 1–2 wk in spring (TJL; see Demography and Populations: Age at First Breeding). For established breeders color-banded on territories, pairs have been observed together year-round (JMK, RDD), though the proportion of adults that remained together from year to year is unknown. An increase in drumming, calling, and male–female interactions in early spring (February–March) correlates with an increase in hormones related to breeding. In Washington, males observed showing attentive behavior to females in early January when in the presence of other unpaired males (JMK).
In gravirostris, cavity excavation occurs primarily in April and early May (KLG). In Oregon, nominate birds begin excavation around 1 May (RDD). In Washington, earliest date found excavating is 22 April (JMK).
Figure 1. Only single broods have been observed. In Washington, multiple instances of replacement clutches after initial nest attempt failure, most often in a newly constructed cavity, but occasionally in same cavity (JMK). Replacement clutches usually occur when first nest fails early in the nesting period. In central Oregon, nests with eggs found 30 May–25 June (RDD). In Washington, earliest observed clutch initiation (first egg laid) was 12 May and the latest was 24 June (after a failed first nest attempt), with a mean clutch initiation date of 28 May (n = 61) (49).
Usually located in dead or partially dead conifers. Multiple studies indicate this species requires substrates with advanced decay to excavate cavities, though decay is not easy to determine from external tree characteristics (116, 117). This species is unusual among cavity excavators for regularly excavating in downed logs (81, 118, 117) and cut stumps left after timber harvest (119, 73, JMK; see ). Also, frequently nests close to the ground (see ) and occasionally excavates cavities on the underside of leaning or downed logs (M. Raphael, unpublished data). Average height of nest of P. a. albolarvatus: 2.5 m (n = 57 nests; Western Foundation of Vertebrate Zoology [WFVZ]); 48 of these nests were in pines, 5 in firs, 3 in aspen, and 1 in alder. Average nest height of P. a. gravirostris: 3.6 m (n = 14; WFVZ). Artificial structures, including fence posts and buildings, are sometimes used (4, 117).
California: Of 11 nests in eastern Sierra Nevada, 9 were in snags, 1 in cut stump < 1.5 m tall, and 1 in fallen log (81). Tree species varied, but about half of nests were in red fir, 3 in Jeffrey pine, and 1 each in lodgepole pine and white fir. Nest trees averaged 65 cm dbh and 3.8 m height. Of 53 nests in the western Sierra Nevada, all but 1 were in completely dead trees (118). Tree height averaged 8 m, dbh averaged 80 cm, and nest height averaged 3.0 m; 28% were in logs or leaning snags; 89% of nests were in pines or firs. All 13 nests of gravirostris in San Gabriel and San Bernardino Mountains, were in conifers (ponderosa, Jeffrey, and Coulter pines; incense cedar, and white fir) except for 2 in snags of California black oak (KLG). Among 48 nests found in burned forest the mean tree diameter was 50.6 cm (SD = 48.1) and mean cavity height was 4.0 m (SD = 2.4) (71).
Oregon: Of 43 nests in central Oregon (72), 36 were in ponderosa pine snags, 2 in ponderosa pine stumps, 2 in quaking aspen snags, and 1 each in live quaking aspen, white-fir snag, and dead top of live ponderosa pine. Nest tree dbh averaged 65 cm, nest tree height averaged 14 m excluding 1 nest 32 m high in dead-topped live ponderosa pine, and nest-cavity height averaged 4.4 m. In south-central Oregon, all 16 nests were in completely dead substrates (37% in snags, 56% in stumps, and 6% in leaning logs) (87). Mean dbh of nest trees was 80 cm and nest tree height averaged 3 m. Among 45 nest sites in burned forest, mean tree diameter was 40.1 cm (70). For 405 nests in the Oregon Cascades mean tree diameter was 68.9 cm (range 14.7–150.6) and mean cavity height was 2.9 m (range 0.5–15.2) (120) .
Washington: For 77 nests in the eastern Cascades, mean diameter of nest trees was 39.7 cm (range 17.8–69.9), mean substrate height was 10.1 m (range 1.4–42.5), and mean cavity height was 3.9 m (range 0.9–15.5) (116). Seventy-two nest cavities were in standing dead substrates, with 83% in ponderosa pine, 13% Douglas-fir, 3% quaking aspen, and 1% grand fir. Of the nests located in live trees, all were in dead portions of the live trees, with 3 in ponderosa pine, 1 in quaking aspen, and 1 in blue elderberry (Sambucus cerulea). For 75 nests in the same region, mean diameter of nest trees was 40.8 cm (range 15.7–94.5) (117) and nest tree species were as follows: 54 in ponderosa pine; 20 in Douglas-fir; 1 excavated in cedar siding of a building. Average elevation of nests was 909.8 m (range 351–1,318).
Both members of pair excavate nest cavity (5), but male appears to do a greater percentage of excavation (JMK); excavation occurs throughout daylight hours. There are numerous “false starts,” resulting in partially excavated but unused cavities (KLG), and some false starts become excavated nest cavities in subsequent years (JMK). Nest-cavity excavation can take 1–4 wk, but most cavities are completed within 1–2 wk, and as soon as 3–4 d in exceptionally soft wood (RDD, JMK, TJL). Occurs mainly in May.
Mean cavity dimensions of 12 nests from the Sierra Nevada, California, were: entrance diameter 46 mm, depth 21 cm, internal diameter 13 cm (81). In central Oregon, mean cavity dimensions were: entrance 50 mm high × 48 mm wide, depth 20 cm, internal diameter 10.1 cm (RDD). At another site in south-central Oregon, mean dimensions were: entrance 48 × 45 mm, depth 25 cm, internal diameter 9.2 cm (RDD).
In Washington, mean internal cavity temperature for woodpecker-excavated cavities was 20.9° C during the summer (SD = 2.9, range 2.0–62.0) (121). Milne and Hejl (118) and Lorenz et al. (117) found no evidence of preferred orientation of nests in the Sierra Nevada and Washington Cascade range, respectively; cavity entrances were uniformly distributed with respect to compass direction. Data from 13 nests of gravirostris in southern California likewise showed no consistent cavity orientation (KLG). In Washington, mean cavity entrance orientation was 298° (n = 77), but entrances were uniformly distributed (JMK). Thus, cavity orientation probably determined more by availability of suitably soft wood for excavating rather than climate benefits.
Maintenance or Reuse of Nests, Alternate Nests
Typically, a new nest cavity is excavated each year (5), although, exceptionally, cavity from previous year may be reused (RDD, JMK). In Washington, one nest cavity in an aspen snag was reused in 3 of 4 years; one cavity was apparently reused in a ponderosa pine snag as no fresh chips were evident on the ground to signify it was a new nest cavity; and one cavity reused for a second clutch after the first clutch failed (116, JMK).
Incomplete nests and “false starts” common in this species (KLG). Outside of breeding season, roosts in old nest cavities; no information on excavation of cavities specifically for roosting.
Oval to subelliptical (4, WFVZ).
Following data from Bent (4). For albolarvatus (n = 50 eggs): length 24.26 mm (range 21.84–26.40); breadth 18.11 mm (range 16.76–19.50). For gravirostris (n = 20 eggs): length 24.67 mm (range 22.62–26.70); breadth 18.60 mm (range 16.67–19.70).
Following data from larger data set of WFVZ. For albolarvatus (n = 93 eggs from 20 clutches): length 24.88 mm (range 22.60–28.12); breadth 18.58 mm (range 17.72–19.71). For gravirostris (n = 41 eggs from 10 clutches): length 24.00 mm (range 21.33–26.66); breadth 18.85 mm (range 17.70–20.98).
Following data from same WFVZ data set, but with means and extremes based on clutch averages. For albolarvatus (n = 20 clutches, 93 eggs): length 24.89 mm (range 22.95–26.87); breadth 18.58 mm (range 18.08–19.56). For gravirostris (n = 37 eggs from 9 clutches): length 23.74 mm (range 21.73–25.33); breadth 18.66 mm (range 17.87–19.56).
Mean initial egg mass reported as 4.4 g, about 7.6% of adult female mass (122). Mean eggshell mass for albolarvatus: 0.310 g (range 0.259–0.346, n = 20 clutches, 93 eggs); mean for gravirostris: 0.298 g (range 0.238–0.342, n = 9 clutches, 37 eggs) (WFVZ).
Color and Surface Texture
White, often becoming washed and spotted with dirt and pitch as incubation proceeds (5, WFVZ). Surface texture smooth, glossy.
Clutch size usually 4–5 eggs. For egg sets of nominate P. a. albolarvatus examined (WFVZ), mean clutch 4.28 eggs (range 2–9, n = 97); 43 (44%) egg sets had 4 eggs, and 35 (36%) had 5 eggs; 3-egg (8%) and 6-egg (5%) clutches also occurred, with single records of 7-egg, 8-egg, and 9-egg clutches (representing > 1 female?). For gravirostris (WFVZ), average clutch 4.1 eggs (range 3–5, n = 10). At a south-central Oregon site, 8 clutches averaged 3.75 eggs ± 0.46 SD (range 3–4, n = 8) (RDD). In Washington, average clutch size 3.9 eggs ± 0.78 SD (range 2–5, n = 51) (49). Generally, only 1 clutch produced per breeding season, but occasionally will renest after failed first nest attempt (JMK).
First egg typically laid soon after completion of nest cavity. Entire clutch usually completed within 5 d.
Onset of Broodiness and Incubation in Relation to Laying
Attentiveness begins with first egg laid (RDD), but timing of onset of incubation unknown; for better-studied congeners, incubation generally begins with last or second-to-last egg laid (5). During laying and before incubation begins, males (and occasionally females) observed to perch inside cavity just below entrance, presumably to guard eggs/cavity from potential predators or other secondary-cavity nesting species such as bluebirds and House Wren (JMK).
Single incubation patch found on abdomen of both sexes of adults. Brood patch present as late as mid-July in Oregon (RDD); refeathering noted 30 June–13 July (RDD).
Both sexes incubate (5), male at night, both sexes during day. Members of pair are highly attentive to each other during incubation, and communicate by soft Drumming both inside and outside of nest cavity, as well as with Double Call and Wad Call. Incubating bird often shifts positions and pecks within cavity (RDD). Incubation exchanges occur every 45–60 min (RDD); when adult is disturbed during incubation, often returns to nest cavity within 3 min (RDD). Typical incubation exchange is as follows (RDD): Male flies in with Wad Calls and lands on branch (if present) or trunk of nest snag; female gives Wad Calls in response; male flies to cavity entrance; female flies out; male enters cavity and begins incubation. This sequence is repeated with the sexes playing opposite roles when female returns to resume incubation activity.
Hardiness of Eggs Against Temperature Stress; Effect of Egg Neglect
Generally asynchronous. One egg frequently does not hatch (RDD). Parents often dispose of eggshells just outside of nest cavity.
Condition at Hatching
Altricial, nidicolous. Psilopaedic (naked), eyes closed at hatching. No data on mass or linear measurements of hatchlings.
Growth and Development
Few data. Quills visible under skin by day 5; pin-feathers erupt through skin by day 12; feathers emerge from sheaths by day 15; fully feathered, with all sheaths broken, by day 19 (RDD). One male nestling 4 d prior to fledging had wing chord 93 mm long and tail 49 mm long (RDD).
Both sexes brood young (5); male broods at night (RDD). Brooding and feeding of young begins immediately after hatching. Typically, parents exchange brooding and feeding duties every 3–10 min. Feeding and brooding bouts sometimes last > 25 min (RDD). In general, parents stop consistently brooding when young are ≥ 10 d old (JMK). Male roosts in nest cavity with young until they fledge.
Both sexes feed young (5, 92). Feeding interval of 15 min reported by Bent (4). In Washington, mean feeding interval was 6.3 min (range 0.13–53.72, n = 682 nest visits) (JMK); provisioning rate did not differ between broods of 2, 3 or 4 nestlings, by age of nestlings, or date of provisioning trip, but it declined as size of the brood increased (92). Also, both sexes provisioned young at the same rate (~1.6 feedings/nestling/hour). No information on amount of food provided to nestlings or distribution of delivered food among nest mates. Adults enter nest cavity completely to feed young until young are about 10–12 d old, after which adults only partly enter cavity. For about 7 days prior to fledging, adults feed young from outside cavity. Young are fed mainly a bolus of insects, including adults and larvae (e.g., ants, bark beetle larvae), unless prey items are large (e.g., cicadas, wood-boring beetle larvae), then prey delivered as a single item (JMK). In the eastern Cascades of Washington, wood-boring beetle larvae (Buprestidae and Cerambycidae), caterpillars, adult ants, and insect larvae comprised 25%, 23%, 18%, and 6% of identifiable prey brought to nestlings, respectively (92). Adults also observed making multiple trips from a backyard bird feeding station to deliver suet to nestlings (JMK).
Both sexes carry fecal material from nest (5, 92). In Washington, males removed fecal material during a greater proportion of nestling feedings than did females (92). When removing fecal material, some wood chips from bottom of cavity are also removed. During the nestling period, adults heard tapping in cavity, presumably to replenish wood chips (JMK). Invertebrate fauna of nests not described.
Parental Carrying of Young
Has never been observed in this species. However, adults have been observed removing dead nestlings from nests (P. C. Fischer, personal communication).
Not known; nonparental adults not normally seen in immediate vicinity of active nests.
Brood Parasitism by Other Species
Departure from Nest
At fledging, bill noticeably shorter than that of adult; 1 gravirostris measured on day of fledging had culmen length of 19.5 mm and bill depth at nostril of 6.5 mm (KLG), approximately 70% of expected adult bill size.
Association with Parents or Other Young
In Washington, radio-tagged young were dependent on parents for food for on average 33.5 d post fledging (SD = 5.5, range 22–45 d, n = 83) and average date of independence was July 29 (range July 9–August 15) (TJL). In Oregon, adults observed feeding fledglings as late as 26 August (RDD). For first several days after fledging, young perch quietly in the forest canopy within ~200 m of nest cavity, with the exception of soft peeping noises when approached by an adult with food (TJL). There is a gradual progression in the mobility of young and by 1–2 wk post-fledging, young are flying confidently behind parents begging (often loudly) for food. Siblings associate in a loose group around one or both adults during the dependent phase (TJL).
Ability to Get Around, Feed, and Care for Self
Flight of recently fledged young noticeably weaker than that of adults. Within 1–2 wk post-fledging, juveniles fly as well as adults, and move about in trees with no apparent difficulty (TJL). Young dependent on parents for approximately 1 mo after fledging (see Association with Parents or Other Young, above), though they have been observed pecking at tree bark as soon as 3 d post-fledging (TJL). Preening has been observed within 5 days of fledging, though this is likely conservative (TJL). Bathing has been observed as soon as 30 d post-fledging; similar to preening, this is likely a conservative estimate and bathing probably occurs earlier but has not been observed. Drumming first observed 15 d post-fledging (TJL).
For movement and behavior during the immature stage from radio-telemetry studies, see Movements and Migration: Dispersal and Site Fidelity. Other aspects of immature stage are not well studied.