USE OF BURROW ENTRANCES TO INDICATE DENSITIES OF TOWNSENDS GROUND-SQUIRRELS

Counts of burrow entrances have been positively correlated with densit ies of semi-fossorial rodents and used as an index of densities. We ev aluated their effectiveness in indexing densities of Townsend's ground squirrels (Spermophilus townsendii) in the Snake River Birds of Prey National Conservation Area (SRBOPNCA), Idaho, by comparing burrow entr ance densities to densities of ground squirrels estimated from livetra pping in 2 consecutive years over which squirrel populations declined by >75%. We did not detect a consistent relation between burrow entran ce counts and ground squirrel density estimates within or among habita t types. Scatter plots indicated that burrow entrances had little pred ictive power at intermediate densities. Burrow entrance counts did not reflect the magnitude of a between-year density decline. Repeated cou nts of entrances late in the squirrels' active season varied in a mann er that would be difficult to use for calibration of transects sampled only once during this period. Annual persistence of burrow entrances varied between habitats. Trained observers were inconsistent in assign ing active-inactive status to entrances. We recommend that burrow entr ance counts not be used as measures or indices of ground squirrel dens ities in shrubsteppe habitats, and that the method be verified thoroug hly before being used in other habitats.