Small mammal species composition data for Niwot Ridge, 1981 - 1990.

Small mammals were live trapped during the summer of each year at
various locations on Niwot Ridge. Species trapped included pikas
(Ochotona princeps), marmots (Marmota flaviventris), deer mice
(Peromyscus maniculatus), voles (Microtus longicaudus, Microtus
montanus, and Phenacomys intermedius), and pocket gophers (Thomomys
talpoides). Pocket gophers were only trapped through the summer of
1983. Mice and voles were trapped using Sherman traps, while
Tomahawk traps were used to trap both the pikas and marmots. Sherman
gopher traps were used to trap gophers. The mice and vole traps were
placed 10 meters apart in parallel rows in grids containing from 25
to 100 traps; weather permitting, these traps were placed for 3
consecutive nights every 1 or 2 weeks from June to August. The
pikas, marmots, and gophers were trapped during late summer of each
year; consult Halfpenny et al. (1984; 1987) for a general
description of these trap locations, as well as descriptions of
baiting and handling techniques and surrounding vegetation
communities. Pika and marmot traps were selectively placed in areas
where evidence of these animals existed. In the case of the pocket
gophers, traps were placed below ground in active mounds. For pikas,
marmots and pocket gophers, traps were set during the day and were
checked every 2 hours. After determining and recording species, sex,
age, reproductive status, weight, health, and trap location, trapped
animals were permanently tagged and released. An additional quality-controlled, derived data-table
(pikas_no_recap.cr.data.csv) was added to the original dataset in
2022. This data table is derived from the original capture data, but
includes only year-unique captures, where each year-unique capture
is the "best" one for comparison with other year-unique
captures. For comparability among years, the best capture for
comparability among years is usually the first capture of the year,
representing the animal's baseline weight for the year (weight
appears to decrease with repeated captures, probably due to
capture-induced stress; this weight-loss is most evident in adults,
because they're no longer growing, but may also retard the normal
weight gain in juveniles). These derived data were prepared by Chris
Ray using several lines of evidence for each determination.