Woodpeckers in the city: Abundances are highest in large green spaces with complex understories

Abstract

We documented occurrence and relative abundance (henceforth abundance) of five woodpecker species in 36 forested green spaces in Portland, Oregon (USA), to estimate minimum area requirements (MAR; 0.5 probability of occurrence) and to test for potential influences of green space area and type (heavily treed manicured green spaces versus undeveloped natural forests), habitat features, and landscape composition on the abundance of woodpeckers. Abundances of all species increased with green space area. Manicured and natural green spaces did not differ in canopy cover or total basal area, but woodpecker abundances were greater in natural than manicured green spaces for all species except Northern Flickers (Colaptes auratus). Flickers and Downy Woodpeckers (Picoides pubescens) were most abundant, MAR of both were under 1.5 ha, and both were found in essentially all green spaces. Hairy (P. villosus) and Pileated (Dryocopus pileatus) woodpeckers were least abundant, and with MAR of 34 and 51 ha, respectively, exhibited pronounced area-sensitivity. Red-breasted Sapsuckers (Sphyrapicus ruber) were intermediate in abundance and MAR to the 2 former and 2 latter species. The most important habitat variables associated with variation in abundance among green spaces were the contribution of deciduous trees to the canopy (Downy Woodpecker [+], Pileated Woodpecker [+] and Northern Flicker [–]), canopy cover (Hairy Woodpecker [+] and Northern Flicker [+]), and log density (Hairy Woodpecker [+], Red-breasted Sapsucker [–]). At the landscape level, lower woodpecker abundance was associated with increased urbanization (Red-breasted Sapsucker and Northern Flicker), while increasing forest cover influenced abundance of Northern Flicker (–) and Pileated Woodpecker (+). Highest woodpecker abundances were thus found in large green spaces with complex understories that were embedded in relatively undeveloped treed landscapes. Management of forested urban green spaces should prioritize needs of the area-sensitive species because ensuring their continued presence benefits the entire avian community.