Use of burrow entrances to indicate densities of Townsend's ground squirrels

Beatrice Van Horne, Robert L. Schooley, Steven T. Knick, Gail S. Olson, Kenneth P. Burnham

Research output: Contribution to journalArticle

Abstract

Counts of burrow entrances have been positively correlated with densities of semi-fossorial rodents and used as an index of densities. We evaluated 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 entrance densities to densities of ground squirrels estimated from livetrapping in 2 consecutive years over which squirrel populations declined by >75%. We did not detect a consistent relation between burrow entrance counts and ground squirrel density estimates within or among habitat types. Scatter plots indicated that burrow entrances had little predictive power at intermediate densities. Burrow entrance counts did not reflect the magnitude of a between-year density decline. Repeated counts of entrances late in the squirrels' active season varied in a manner 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 assigning active-inactive status to entrances. We recommend that burrow entrance counts not be used as measures or indices of ground squirrel densities in shrubsteppe habitats, and that the method be verified thoroughly before being used in other habitats.

Original languageEnglish (US)
Pages (from-to)92-101
Number of pages10
JournalJournal of Wildlife Management
Volume61
Issue number1
DOIs
StatePublished - Jan 1997
Externally publishedYes

Keywords

  • Snake River Birds of Prey National Conservation Area
  • Spermophilus townsendii
  • Townsend's ground squirrel
  • burrow entrance counts
  • census
  • mark-recapture
  • observer bias
  • population indices

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Ecology
  • Nature and Landscape Conservation

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