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

摘要

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 vs. 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. Lay Summary center dot Woodpeckers provide ecosystem services by acting as ecosystem engineers, habitat modifiers, and facilitator species. However, we know little about woodpecker requirements for persistence in urban settings. center dot We documented minimum area requirements (MAR) and sources of variation in abundance of 5 woodpecker species in 36 green spaces in Portland, Oregon, in 2015 and 2016. center dot Except for the ground-foraging Northern Flicker, MAR increased with body size, ranging from 1.3 ha for the small Downy Woodpeckers (27.5 g) to 51 ha for the large Pileated Woodpecker (300 g). center dot Abundance of all species increased with green space area, and except for Northern Flickers, was higher in natural than manicured green spaces. center dot Species responses to habitat and landscape variables differed, but abundances were generally higher in green spaces with high basal area of deciduous trees, closed canopy, and where landscapes were less urbanized and had higher tree cover. center dot Management policies should be driven by the needs of species with the largest MAR and greatest dependence on structurally complex vegetation structure.