RESPONSE OF THE AMERICAN DIPPER (CINCLUS MEXICANUS) TO DECREASED STREAM WATER QUALITY.

J.M. Feck and R.O. Hall, Jr.. Department of Zoology and Physiology, University of Wyoming, Laramie, WY, 82071.

Dippers, Cinclus spp., are conspicuous, non-migratory, stream obligates found worldwide. These birds are currently not used in stream bioassessment, yet they should respond to decreases in water quality because they forage preferentially on large macroinvertebrates in clear-water streams. We hypothesized the presence of dippers may indicate increased water quality as measured by invertebrate bioindices and sedimentation. We analyzed 32 pairs of nesting dippers in the Wind River mountains, Wyoming. We caught and color banded dippers. We measured dipper territory size, and related this to invertebrate assemblages, water chemistry, and geomorphology of streams. Dipper territory size was significantly negatively related to Plecoptera abundance, and positively related to non-insect abundance and silt, suggesting dippers forage over shorter distances in streams with more Plecoptera and fewer non-insects and silt. We analyzed benthic macroinvertebrates from 16 sites with suitable nesting habitat, but no dippers to estimate if altered macroinvertebrate assemblages cause dipper absence. Dipper presence was significantly positively related to Plecoptera abundance, and negatively related to Oligochaeta abundance and specific conductivity, suggesting dippers prefer increased Plecoptera, decreased oligochaetes, and lower conductivity. Dippers quantitatively reflect disturbance as measured by stream bioassessment indices, showing that impairment within the stream can affect this semi-aquatic bird.