SGS-LTER Long-Term Monitoring Project: Small Mammals on Trapping Webs on the Central Plains Experimental Range, Nunn, Colorado, USA 1994 -2006, ARS Study Number 118

This data package was produced by researchers
working on the Shortgrass Steppe Long Term
Ecological Research (SGS-LTER) Project,
administered at Colorado State University.
Long-term datasets and background information
(proposals, reports, photographs, etc.) on the
SGS-LTER project are contained in a comprehensive
project collection within the Digital Collections
of Colorado
(http://digitool.library.colostate.edu/R/?func=collections&collection_id=3429).
The data table and associated metadata document,
which is generated in Ecological Metadata
Language, may be available through other
repositories serving the ecological research
community and represent components of the larger
SGS-LTER project collection. Additional information and referenced materials can be found:
http://hdl.handle.net/10217/83452. Small mammals (rabbits, rodents) are integral
components of semiarid ecosystems because of their
roles as consumers of plants, seeds and
arthropods, as soil disturbance agents, and as
food for raptors, snakes and mammalian carnivores.
Because of their vagility and intermediate trophic
position, populations of small mammals may track
changes in vegetation and the abiotic environment
that may result from shifts in land-use and other
anthropogenic disturbances. However, these
populations are variable over space and time, and
their response to environmental changes may not be
immediately apparent given their behavioral
flexibility and relatively long life-spans and
generation times. Patterns in the distribution and
abundance of small mammals thus may simultaneously
reflect and affect the stability of the
shortgrass-steppe ecosystem. Long-term studies of
population and community dynamics therefore are
needed to fully understand the role of small
mammals in grassland ecosystems. In 1994, we
implemented a sampling scheme to monitor long-term
changes in relative abundance of small mammals in
representative habitats of shortgrass steppe. We
live-trapped nocturnal rodents twice each year
(spring, late summer) on trapping webs in upland
prairie (GRASS) and saltbush-dominated (SHRUB)
habitats. Three 3.14-ha webs were established in
each habitat. Each web had 124 Sherman traps,
which were spaced 10-m apart on 12 100-m spokes,
with 30 degrees between spokes. Four traps were
set in the center of the web. Traps were set for
four consecutive nights in each trapping session.
Traps are baited with a mix of peanut butter and
oats, set in the evening and checked (and closed)
at dawn. We recorded sex, age and weight upon
first capture of all individuals. In the early
years of the study, individuals were batch-marked
(Sharpie colored felt markers) to distinguish
recaptures from new individuals, providing the
minimum information necessary to use
distance-sampling methods to estimate density.
Most nocturnal species are now usually marked with
aluminum ear tags, although we continue to mark
very small (pocket mice) or small-eared (voles)
species only with felt pens. For ear-tagged
animals, we distinguish new captures (N) from
individuals marked during previous sessions (old,
O), versus those that are recaptured (R) on 2nd,
3rd or 4th nights of a trapping session. The
location of one trapping web was changed from 13NE
(1994-1997) to 13SW (1998- present) because of
concerns about intensive cattle use in the
pasture, as well as activity of CPER Site
Manager’s cats.