Is it a Pocket Gopher or Mole?
by Wendy M. Arjo
National
Wildlife Research Center’s Olympia Field Station
Depending on where you are, the term
“gopher” is applied to a variety of mammal species
including ground squirrels, prairie dogs and moles. The
true pocket gopher is actually very distinguishable once
you recognize their appearance and sign, or indicators of
the animal. Pocket gophers are burrowing rodents named for
their external fur-lined cheek pouches. Unlike mole mounds,
which have been characterized as miniature volcanoes,
gopher mounds are fan-shaped in appearance. Pocket gophers
are distributed throughout the Pacific Northwest, but occur
more frequently in the drier climates of eastern Washington
and Oregon.
Pocket gophers prefer roots and stems of
herbaceous annuals and perennial plants that are often
associated with early successional forests. Because of this
preference, seedlings become a very tempting target to a
foraging pocket gopher. Commonly, gophers will prune
seedling roots and often pull the entire seedling into
their burrow. Stem clipping at ground level and girdling
are also common with seedlings less than half an inch in
diameter the most vulnerable. In deep snow conditions,
aboveground girdling of larger trees can occur. Although
aboveground girdling is easy to detect, damage by pocket
gophers to root systems may go unnoticed until seedlings
become discolored or tip over. Several factors have been
noted that predispose a stand to pocket gopher damage:
1) current pocket gopher density;
2) soil suitability for burrowing;
3) topography;
4) herbaceous understory;
5) amount of adjacent border with preferred forage; and
6) site preparation.
Management practices to reduce pocket
gopher damage include silvicultural practices, such as
minimizing disturbance of an area, habitat manipulation,
trapping, repellents, fumigation and seedling barriers such
as Vexar tubing. Strychnine baiting is the most widely used
method to reduce pocket gopher populations prior to
planting seedlings. Baits are applied belowground to
minimize negative impacts on aboveground non-target
species; strychnine-baited pocket gophers, however, may
still pose a threat to subterranean predators such as
weasels. In addition, pocket gophers and other small
mammals using pocket gopher bur-rows may consume the bait
and die aboveground.
The Olympia Field Station has conducted
several tests to determine primary, secondary and tertiary
risks that may occur while strychnine-bait-ing pocket
gophers. This supports the notion that fossorial (living
below-ground) rodents baited belowground are unlikely to
become secondary hazards. However, this does not entirely
eliminate the chance of an occasional aboveground death or
the potential for underground predators like weasels to
encounter carcasses. Predator-prey interactions are largely
unknown since subterranean predator activity is difficult
to observe. If strychnine-baited pocket gophers die
aboveground, secondary hazards to scavengers and tertiary
hazards to insectivores (species that eat insects that
cause decay of carcasses), may occur. Fly larvae and ants
were found to contain high levels of strychnine; however,
little risk is posed to insectivores due to the quantity of
insects that would have to be consumed to acquire a lethal
dose. Studies by the Olympia Field Station have shown that
controlling pocket gopher populations with strychnine
baiting poses relatively little risk to non-target species.
SOURCE:
Society of American Foresters
Western
Forester 48(4)
2003