SPECIES

White-headed Woodpecker Dryobates albolarvatus

Jeffrey M. Kozma, Teresa J. Lorenz, Martin G. Raphael, Kimball L. Garrett, and Rita D. Dixon
Version: 2.0 — Published July 9, 2020

Demography and Populations

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Measures of Breeding Activity

Age at First Breeding

This species may nest during the first year after hatching (as second-year birds), but not all second-year birds breed. Among 83 nestling White-headed Woodpeckers radio-tagged in Washington (2014–2017), 10 survived their first winter and were tracked in their first breeding season (March–July) (TJL). Among these 10 birds, 7 attempted breeding and 4 successfully fledged young. Five were female and all 5 nested in their first year; 5 were male and only 2 nested in their first year. Two of these males were observed breeding in later years (identified by color bands after radio-transmitter died). One male nested successfully in his second breeding season and 1 male did not attempt nesting until his third breeding season.

Clutch

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).

Annual and Lifetime Reproductive Success

In Oregon and Washington, 1–3 young are typically fledged/successful pair/yr. Nest success (at least 1 young fledged) in central Oregon: 83% (n = 41); in south-central Oregon: 87.5% (n = 16). In Washington, an average of 2.6 young ± 0.76 SD (n = 47 nests) fledged/successful pair/yr, with a period survival rate (laying period + incubation period + nestling period) of 0.70 (n = 55 nests); nest survival declined as shrub cover increased (49). Similarly, Lorenz et al. (67) reported a mean of 2.2 ± 1.2 fledglings per nest. In burned forest of Oregon, nesting success was estimated at 76% with a daily survival rate of 0.993 (70). Number of young fledged smaller than clutch size because one egg (last laid?) may not hatch or one nestling (last to hatch?) often does not survive (JMK).

No data on lifetime reproductive success.

Life Span and Survivorship

In Washington, one breeding male color-banded as an after-second-year bird was found on the same territory until it was at least 9 yr 7 mo old and another breeding male color-banded as an after-third-year bird was found on the same territory until it was at least 7 yr old (JMK). Also in Washington, a female color-banded as a hatch-year bird was resighted at 6 yr 11 mo in age (123).

Using unpublished data from radio-telemetry, the period survival rate of adults (n = 35) from May–November in Washington was 0.83 in both 2011 and 2012 (124). Of these 35 radio-tracked White-headed Woodpeckers aged from flight-feather molt patterns (7), the age structure was as follows: 6 were second-year birds; 4 were third-year birds; 21 were ≥ 3 yr old; and 3 were ≥ 4 yr old (67). Using telemetry data from two unpublished studies in central Oregon, the period survival rate was 0.81 (n = 12) (87) and 0.80 (n = 19) (72). In Washington, the probability of a radio-tagged juvenile surviving to 150 d post-fledging was 0.59 (n = 83; 86). There was variation in survival rates by study area (P = 0.01) and year (P < 0.01), but juvenile survival did not differ for birds observed foraging on ponderosa pine cones compared to those not seen foraging on ponderosa pine cones (P = 0.39).

Disease and Body Parasites

Little information available. Lice (on wings, tail, body), mites, and hippoboscid flies found on mist-netted birds in Oregon (RDD). There is one case study documenting Haemoproteus velans (Haemosporida, Haemoproteidae), a blood parasite transmitted by biting midges (Diptera: Ceratopogonidae), as the cause of death in a juvenile White-headed Woodpecker (114).

Causes of Mortality

For details regarding predation of adults, juveniles, nestlings, and eggs, see Behavior: Predation. Evidence points to raptors (Accipiter spp.) being the main predators of adults and juveniles, though there are no studies with large sample sizes; most reports of causes of mortality are anecdotal. For anthropogenic factors, deaths from collisions with automobiles have been recorded in Oregon (RDD), southern California (KLG), and south-central Washington (TJL). In Washington, a nestling died when it became entrapped in insulation netting at a nest excavated in the siding of a cabin (TJL).

Population Spatial Metrics

Individual Distance

Members of pair routinely forage within 3–5 m of each other (occasionally 1 m), but individual distances among unpaired adults normally much greater (RDD, KLG). One to three dependent juveniles commonly follow adults very closely (< 1 m) between foraging sites in trees while calling loudly, such as while foraging in foliage clusters of ponderosa pine, occasionally subplanting adults from a foraging site. Juveniles will closely follow adults even when flying between trees (TJL).

Territory Size

The size of area that is actively defended against other breeding pairs is unknown and varies based on the suitability of habitat, date within the breeding season, and individual disposition. Lorenz et al. (67) estimated that 50% core areas averaged 23.4 ha during the breeding season, compared to 124.9 ha for the 95% home range. Some defense of home range has been seen outside the breeding season (RDD), but territoriality appears relaxed after the breeding season as evidenced by unsuccessfully nesting adults and juveniles foraging in close proximity during August–September (JMK). In Washington, nest sites of simultaneously nesting pairs documented as close as 160 m from each other (JMK). Also in Washington for radio-tagged woodpeckers, Lorenz et al. (67) reported nearest neighbor distances between nests were 106–2,723 m. In suitable habitat, 95% home range kernels frequently overlap, even during the breeding season (67).

Winter territories have not been formally studied.

Home Range Size

In central Oregon, mean home range 104 ha (range 67–63 ha) on continuous old-growth sites and 321 ha (range 57–445) on fragmented sites (n = 18; 72); in south-central Oregon, mean home range 212 ha (range 172–324) in predominantly old-growth sites and 342 ha (range 171–704) on fragmented sites, based on telemetry studies (n = 12) (87). In Idaho, home ranges estimated from 90% kernels averaged 91 ha ± 43.9 SD (range 24.3−169.2) (125). Ranges from 100% minimum convex polygons averaged 70.8 ha ± 26.5 SD (range 37.6−121.7) (125). In south-central Washington in ponderosa pine-dominated forests with a history of timber harvest and prescribed fire, mean home range during the nesting period (May–July) was 125 ha ± 59 SD (n = 19) and during the post-nesting period (July–October) was 137 ha ± 70 SD (n = 30) (67). During the nesting season, home ranges for 11 neighbors overlapped on average by 22.6% (range 0.1–91) and during the post nesting season, home ranges of 15 neighbors overlapped by 28.7% (range 7.3–56.5) (67). During the time when juveniles are still dependent on their parents in late summer, the mean home range size of juveniles was 60.9 ha (range 6.2–251.4) (TJL). On average, autumn home range size for juveniles estimated from minimum convex polygons was 28.8 km2 ± 27.4 SD (range 1.0–108.8, n = 52). As second-year birds, spring (non-breeding) home range size averaged 7.4 km2 ± 14.4 SD (range 0.2–49.5, n = 10) (TJL).

Population Status

Numbers

Total population size in the United States is 240,000 individuals (95% CI: 170,000–340,000) (126). The annual breeding population in British Columbia is believed to be very small, perhaps just 10 breeding pairs (127).

Densities appear to increase southward through the range. The White-headed Woodpecker is rare in British Columbia, relatively uncommon where it occurs in Washington and Idaho, and more common in California. Breeding Bird Census data for an old-growth mixed-conifer/red fir site in western Sierra Nevada, Fresno County, California, yielded high densities of 3.0–5.5 territories/40 ha from 1988 to 1992 (128). A Breeding Bird Survey route through 40 km of mixed-conifer forest in San Gabriel Mountains, California, yielded mean of 9.9 individuals/survey (range 6–16) over 17 survey years (1978–1995); birds were encountered on 8.29 stops/survey (16.6% of stops), range 5–14 stops (KLG). Raphael and White (129) reviewed all Breeding Bird Censuses of forest plots in the Sierra Nevada, California, published in American Birds from 1948 to 1978 and found average density of 2.3 pairs/40 ha (range 0.1–5.0) where species occurred. Raphael and White (129) conducted spot-map surveys on 8 plots in northern California and estimated maximum density of 1.2 pairs/40 ha. Raphael et al. (82, 130) reported an average of < 0.1 pairs/40 ha on a burned plot that was periodically surveyed from 1966 to 2014. Density varied from 0 to 1.0 pairs/40 ha on an adjacent unburned plot over the same period.

In south-central Oregon, Dixon (87) reported densities based on point-count data of 0–2.53 birds/40 ha (n = 15 sites). Densities based on absolute counts of breeding pairs: 0.18–0.49 birds/40 ha in south-central Oregon (n = 3), and 0.52–1.06 birds/40 ha in central Oregon (n = 4; RDD). In northeastern Oregon, Mannan and Meslow (131) found densities of 0.5 birds/40.5 ha in managed mixed-coniferous forests and 1.0 birds/40.5 ha in old-growth mixed-conifer forests. In ponderosa pine and mixed-conifer forests of central Oregon, Frenzel (120) found densities of 0–0.69 territories/40 ha.

In a south-central Washington study area comprised of ponderosa pine forest with a long history of being managed for timber production, density of breeding pairs based on an absolute count was 0.5 pairs/40 ha (JMK).

Trends

Survey-wide data from the North American Breeding Bird Survey (BBS) indicated a mean annual increase of 0.8% (95% CI: 0.0, 1.7) from 1968 to 2017 (132). Over the same time period, BBS data suggested that populations in California increased by 1.0% per year (95% CI: 0.0, 1.9). BBS data also showed an annual increase of 0.4% for Oregon, but this increase was not statistically significant as the confidence interval (95% CI: -1.6, 2.7) overlaps zero. Similarly, the population trend for Washington increased 0.8% per year, but the confidence interval overlaps zero (95% CI: -2.4, 6.2). Over a 45-yr period (1970–2014), BBS data indicated that the overall population increased by an estimated 65% (133).

Population Regulation

Species appears K-selected, with relatively stable numbers in suitable breeding habitat. Fluctuations in food (arthropods or pine cones) availability in fall and winter seem likely to affect overwinter survival, though no research has been conducted regarding the effects of food availability on survival. Nest sites may be limiting where forestry practices involve removal of stumps and snags. Snag abundance on non-federal forests in Oregon and Washington was estimated to only be sufficient to support 10–20% of the maximum potential population of the White-headed Woodpecker (134). More recently in Washington, it was estimated that 86% of available snags (n = 360) in White-headed Woodpecker territories were unsuitable for cavity excavation due to the wood being too hard (i.e., undecayed) (117); thus, not all snags on the landscape can be used for nesting. Availability of suitable snags for cavity excavation may limit nesting potential in areas where snag densities are low or where snags are harvested for firewood or other purposes.

Recommended Citation

Kozma, J. M., T. J. Lorenz, M. G. Raphael, K. L. Garrett, and R. D. Dixon (2020). White-headed Woodpecker (Dryobates albolarvatus), version 2.0. In Birds of the World (P. G. Rodewald and B. K. Keeney, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.whhwoo.02