Status and conservation of white-headed woodpecker (Picoides albolarvatus) in the Interior West, USA: A metapopulation approach.

摘要

The White-headed Woodpecker (Picoides albolarvatus) is endemic to pine-dominated (Pinus spp.) forests in the mountainous regions of the West. Coniferous forests east of the Cascade crest in the Pacific Northwest have undergone dramatic physiognomic changes in the last 100 years. Silvicultural practices and changes in natural disturbance regimes have led to the overall decline of eastside old-growth ponderosa pine (Pinus ponderosa) forests. Using the variable circular-plot (VCP) method, I assessed the density, distribution, and habitat characteristics of White-headed Woodpeckers at sampling locations (points) systematically spaced at 0.8-km intervals along randomly selected transects within tracts of ponderosa pine forest types in the Interior Columbia River Basin, USA, in spring 1998. Density estimates for White-headed Woodpeckers across composite habitat types (forest cover type x stand structure class) ranged from 0.00--0.08 birds ha-1 (x = 0.03, 95% CI 0.01--0.05). I used the Kaplan-Meier staggered entry procedure to estimate survival rates of White-headed Woodpecker eggs, nestlings, fledglings, and radiotagged adults in Oregon, USA. To identify key life stages that influence the long-term population dynamics of this rare bird associated with large-diameter ponderosa pine forest types, I conducted a sensitivity analysis on demographic data from two White-headed Woodpecker populations in central and south-central Oregon. I calculated the elasticity associated with each age-specific vital rate based on 500 randomly-generated replicates of a stochastic Leslie matrix model. Age 1 fecundity and age 0 survival were associated with highest elasticity of lambda for 63% and 37% of the replicates, respectively. The mean finite rate of increase (lambda) associated with these elasticities was 1.23 (95% CI 1.20 to 1.27), which indicates that the population is increasing at an annual rate of 23%. The sensitivity analysis indicated that age 0 survival and age 1 fecundity were critical determinants of White-headed Woodpecker population trend. From this, future research on White-headed Woodpecker should focus on determining the causes of nestling mortality and first year productivity. Finally, I present an exploratory metapopulation analysis of the White-headed Woodpecker in the Interior Columbia River Basin.