Can observer clothing color affect estimates of richness and abundance? An experiment with point counts

Abstract

Abstract Red-plumaged birds (red species) may behave more visibly in the presence of a red-orange safety vest that field observers must often wear, but species lacking red plumage (non-red species) may behave less visibly (i.e., the species-confidence hypothesis). Such responses may bias many common counting techniques. We experimentally tested if observer clothing color could affect richness and abundance variables derived from point counts. During summer and winter, we surveyed point-count stations while alternately wearing a red/orange vest (vest counts) and not wearing a vest (control counts). Winter estimates of species richness, total abundance, abundance of non-red species as a group, and the White-breasted Nuthatch (Sitta carolinensis) were significantly lower when the vest was worn, but red species were not significantly different. We did not observe any significant effects of the vest during summer counts. Power was high for community-level variables and intermediate for non-red species, but low...