Northern Idaho ground squirrel population monitoring progress report for the 2012 field season

Publication Type:

Report

Authors:

Source:

Threatened and Endangered Species Projects E-28-10 & E-28-11, Idaho Department of Fish and Game Boise, Boise, p.15 (2012)

Call Number:

U12WAG01IDUS

Keywords:

northern Idaho ground squirrel, Spermophilus brunneus brunneus, Urocitellus brunneus

Abstract:

Population monitoring of the federally threatened northern Idaho ground squirrel (Urocitellus brunneus brunneus) continued in 2012. We conducted capture-mark-recapture at 10 sites and estimated numbers at these sites with a POPAN analysis in Program MARK. We captured 353 adult and yearling squirrels, resulting in a modeled population estimate of 603 for these 10 sites. For comparison, we conducted line-transect distance sampling across these same 10 sites and used program DISTANCE v6.0 to estimate a population size of 186 squirrels. Overall we detected twice as many squirrels trapping (3 visits to each site) than we observed with a one-time survey. Site-specific proportions of survey-to-trap numbers were variable. The point estimate of population size from the capture-based MARK analysis was almost 2x greater than the actual number of squirrels trapped, and 3x greater than the survey-based DISTANCE estimate for the same 10 sites. We continued to explore new approaches to surveying all known occupied sites as a transition to a more systematic long-term monitoring approach. We conducted line-transect distance sampling at a stratified random sample of transect lines totaling 200 km of linear length, or 56% of the total length available. We used program DISTANCE v6.0 to estimate population size. We estimated a population of 1,374 squirrels in stratum 1 (higher-density sites), 662 in stratum 2 (lower-density sites), and an overall population estimate of 2,036 squirrels. This estimate was ~35% higher than 2011 using different methods. Northern Idaho ground squirrels occupied 53 of the 60 known sites in 2012. New locations were discovered in the Lost Valley Reservoir area adjacent to known occupied habitat. Columbian ground squirrels and badgers were detected at 32 and 8 sites, respectively. A distance-based line-transect survey protocol will continue to be refined over the following months with the overarching goal of establishing a long-term monitoring design for the northern Idaho ground squirrel population.