Human Influence on Avian Assemblages Along the Snake River, Wyoming

Abstract

We conducted bird surveys during the breeding season on eleven 100-m strip transects located within areas used heavily by humans. Bird abundance and composition were then compared to eleven 100-m strip transects of similar vegetation composition and structure to determine what effect human intrusion had upon avian communities. Human-use areas had similar vegetation structure (tree stem density, tree dbh, shrub density, nearest tree, largest log, canopy cover, ground cover, vertical and horizontal cover, and canopy height) and composition (number of snags and plant species) according to statistical analysis (P ≥ 0.05). Observed differences in avian species composition and abundance could therefore be attributed to the presence of humans. We compared species richness and relative abundance of birds in both treatments. Thirty-six of the 77 avian species observed (47%) were significantly less abundant where human use was prevalent. The following decreases in avian species richness were observed in the six cover types studied when human use was present: lodgepole pine (Pinus contorta) (three species), Engelmann spruce (Picea engelmannii) (four), willow (Salix sp .) (seven), narrowleaf cottonwood (Populus angustifolia) (nine), big sagebrush (Artemisia tridentat) (nine), and cottonwood/conifer mixture (11). Nine bird species were more abundant in human-use areas: downy woodpecker (Picoides pubescens), hairy woodpecker (Picoides villosus), dusky flycatcher (Empidonax oberholseri), common raven (Corvus corax), black-capped chickadee (Parus atricapillus), American redstart (Setophaga ruticilla), green-tailed towhee (Pipilo chlorurus), Brewer's blackbird (Euphagus cyanocephalus), and brown-headed cowbird (Molothrus ater). Only the common raven (P = 0.002) and black-capped chickadee (P = 0.035) were significantly more abundant in human-use areas.