WTPD Conservation Assessment - Endangered Species & Wetlands ...

changes in occupied habitat within each State at selected sites. Both data sets have weaknesses
and limitations as described below, but are the best available data for this assessment. The
incorporation of both data sources provided a more complete assessment of the range-wide status
of the white-tailed prairie dog by describing changes not only with regard to numbers of animals
but also examining the distribution of occupied habitat across the range.
The Colorado, Montana and Utah sections were evaluated with the methods described
below and were authored by Amy Seglund. The Wyoming section was written by Martin
Grenier and Bob Luce.
Methods
Population Analysis
In 1981 with the discovery of black-footed ferrets at Meeteetse, Wyoming, States within
the historic range of this species initiated programs to identify complexes (Appendix I) of
white-tailed prairie dogs as potential reintroduction sites for black-footed ferrets (Figure 2).
Because white-tailed prairie dogs and black-footed ferrets occur sympatrically, evaluation of
suitable habitat for black-footed ferrets is dependent on describing white-tailed prairie dog
factors such as size and spatial arrangement of colonies and densities of prairie dogs within these
areas (Forrest et al. 1985, Biggins et al. 1989, 1993). To aid in evaluation of prairie dog habitat,
Biggins et al. (1989, 1993) developed a technique that involved counting active burrows within
1 km x 3 m transects distributed over colonies. Transects were designed to sample the mean
burrow density for an entire complex within 10% at the 95% confidence level. The number of
active burrows was then converted from burrows to prairie dog counts and finally to an estimate
of density. This method (Biggins et al. 1989, 1993) also attempted to define and standardize
mapping of colonies and complexes. Because this method has been consistently used at
black-footed ferret reintroduction sites and no other long-term monitoring data are available, the
evaluation of temporal population changes of white-tailed prairie dog populations is based on
surveys conducted at black-footed ferret reintroduction sites.
Concerns were raised among the White-tailed Prairie Dog Working Group members
regarding the use of the black-footed ferret survey data to evaluate the status of white-tailed
prairie dog populations due to the questionable correlation between counts of active burrows and
densities of animals. A review of the literature found that Severson and Plumb (1998), Menkens
(1987) and Powell et al. (1994) did not find a relationship between burrow density and above
ground counts of either white-tailed or black-tailed prairie dogs. Similarly, Van Horne et al.
(1997) did not detect a consistent relationship between burrow entrance counts and Townsend’s
ground squirrel (Spermophilus townsendii) population estimates. These authors recommended
that burrow counts not be used to index population density unless first thoroughly verified.
However, other studies involving ground squirrels (Owings and Borchert 1975, Nydegger and
Smith 1986, Weddell 1989 in Van Horne et al. 1997) correlated counts of burrows with densities.
The reason for discrepancies among studies may be the result of a number of factors.
One may be an observer’s ability to reliably differentiate between active and inactive burrows.
Biggins et al. (1989, 1993) defines active prairie dog burrows as those that have fresh fecal
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