Effects of observers using different methods upon the total population estimates of two resident island birds

Abstract

During a 5-week study of the Nihoa Millerbird and Nihoa Finch, we censused birds using these techniques: two line transect methods, a variable-distance circular plot method, and spot-mapping of territories (millerbirds only). Densities derived from these methods varied greatly. Due to differences in behavior, it appeared that the two species reacted differently to the observer. Millerbirds appeared to be attracted to a moving observer, perhaps to forage on insects; finches appeared to be attracted to a stationary observer in order to feed on seabird eggs temporarily abandoned during the count. Although these behaviors may be unusual, they dramatically demonstrate that no single census method will suffice for all species. The method that assures the least observer effect will provide the most accurate population estimate.

Citation

Conant, Sheila; Collins, Mark S.; Ralph, C. John. 1981. Effects of observers using different methods upon the total population estimates of two resident island birds. Studies in Avian Biology No. 6:377-381