CHANGES IN BIRD COMMUNITIES AND WILLOW HABITATS ASSOCIATED WITH FED ELK

摘要

I assessed changes in bird distributions associated with alteration of riparian willow (Salix spp.) habitat by supplementally-fed elk (Cervus elaphus nelsoni) in western Wyoming, USA. Bird communities in stands close to (n = 4) and distant from (n = 4) feeding stations were dissimilar (complement of the Morisita-Horn index = 0.27). Stands close to feeding stations had lower species richness and relative abundances of all birds while relative abundances of all shrub-steppe species were greater, an effect of elk-induced conversion of willow to shrub-steppe habitat. Elk affected habitat mainly by reducing willow cover < 2 m in height. Reductions in willow cover at > 0.5-l and > l-2 m, relative to 11 alternative variables, were responsible for declines in Willow Flycatchers (Empidonax traillii), MacGillivray's Warblers (Oporornis tolmiei), and Fox Sparrows (Passerella iliaca). Elk feeding in the Gros Ventre River Valley had reduced but similar effects on birds and habitat despite a smaller number of elk fed (1,900 vs. 9,200 annually for 1994-1998) and a shorter duration of feeding (initiation in 1960 vs. 1912) relative to the National Elk Refuge. These effects can extend at least 1.5 km.