Frequently Asked
Burrowing
Animal Management
Q u e s t i o n s
Despite an aggressive program by the Santa Clara
Valley Water District to protect levees from erosion
and other hazards, some levees in the county are
threatened by ground squirrels and other rodents.
Not to be confused with tree squirrels, ground
squirrels dig burrows for shelter and safety. As
burrows grow deeper and expand laterally, they
weaken levees, ditch banks and earthen dams, as
well as undermine roadways and buildings.
1. How damaging can a ground
squirrel or other rodent be?
Ground squirrels live in colonies that may include
several dozen individuals in a complex of burrows.
They can be very damaging to native vegetation
along streams. Ground squirrels eat grain, nuts and fruits, devour plants in their seedling stage and gnaw
on tree bark, twigs and leaves. Ground squirrels’ burrows — which can grow to 30
feet or more in length and may extend two to four feet below ground— undermine levees, roadways
and structures, endangering wildlife habitat and
public safety. They can also harbor harmful diseases,
including bubonic plague, which is transmitted
to humans by fleas carried by squirrels and other
rodents.
2. What are the options for
controlling burrowing animals?
Control options are heavily influenced by the unique
life cycle and behavior of ground squirrels.
Baiting — using treated grain to poison squirrels —
is most effective in summer and fall when squirrels
primarily feed on seeds. Fumigation — using a
gas pumped into burrows to kill squirrels — is most
effective in spring when soil is moist and the squirrels
have not yet begun to reproduce.
Temporary, emergency fix from burrowing animals on
Sunnyvale West Channel during high tides and winter
storms in 2005. Plastic sheeting was used to stop water
from flowing through the levee.
Trapping is only practical when dealing with
very small squirrel populations. Predators —
hawks, eagles, rattlesnakes and coyotes — eat
ground squirrels, but are not able to keep squirrel
populations low enough to prevent damage.
3. What methods are used by
the water district?
The water district contracts with a qualified pestmanagement firm to bait burrows near levees
during appropriate times of the year. Applications
follow best management practices, known as
BMPs, established by the University of California to
safeguard sensitive wildlife and humans.
continued on back...
4. Isn’t the bait poisonous to
others?
Anticoagulants are the bait of choice because of their
effectiveness and relative safety to humans and pets.
However, they are effective only when consumed in
several feedings over a period of five or more days.
Their effectiveness is significantly reduced if 48 hours or
more is allowed to elapse between feedings. Because
close monitoring is required when using anticoagulants
and because of an antidote (vitamin K1), the water
district prefers anticoagulants over more toxic baits.
5. Is bait used for squirrels
affecting other wildlife?
7. Have burrowing animals
caused problems in other places
as well?
A post-Katrina study by the University of California,
Berkeley cited rodent burrows as a “pervasive
problem” with earthen levees in New Orleans. The
California Department of Water Resources 2005
white paper “Flood Warnings: Responding to
California’s Flood Crisis” lists animal burrows as one
key factor in levee degradation statewide. The U.S.
Army Corps of Engineers routinely requires its local
partners nationwide to perform burrow control on
federally built and funded levees.
As an added layer of safety, the water district uses
bait boxes — small structures that squirrels must enter
to eat the bait. Bait boxes are the preferred method
around homes and other areas where children, pets
and other wildlife are present. Although it is more
popular and less expensive to broadcast, or spread,
bait for squirrels to pick up as they forage for seeds,
using bait boxes greatly reduces the chance of birds
ingesting toxic bait. The district’s pest-control firm
monitors burrows before baiting, and visits the site
often after applications to retrieve carcasses before
they can be consumed by scavengers.
6. How do the bait stations
affect the environment?
The water district’s rodent control program was
thoroughly vetted with environmental stakeholders,
including state and federal regulators, in the district’s
Stream Maintenance Program Environmental Impact
Report. It is one of the most environmentally sensitive
programs of its type in the state. Other rodent-control
methods are less selective and have a much higher
potential of harming other animals. Bait stations are
more effective because they can be modified to be
species-specific.
Secured bait station.
What we do
The Santa Clara Valley Water District manages water
resources and provides stewardship for the county’s
five watersheds, including 10 reservoirs, hundreds of
miles of streams and groundwater basins. The water
district also provides flood protection throughout
Santa Clara County.
Visit our website, www.valleywater.org.
Contact us
If you have questions or concerns about this topic,
contact Project Manager Ray Fields at (408)
265-2607, ext. 3027.
Active ground squirrel burrow in levee.
© 2010 Santa Clara Valley Water District • 08/12/10 EM