Bats at Capitol Lake
Every night from May through September thousands of bats feed on insects
over Capitol Lake in the center of Washington State’s capitol city, Olympia.
While the lake reflects the Capitol Dome in the dusk, bats are weaving
back and forth over the lake as they eat, staying for up to six hours
a night. It’s “women and children first” for these bats. While pregnant
and nursing females feed at Capitol Lake, the males are found at higher,
cooler elevations, benefiting our forests by eating insects there.
The regular visitors to Capitol Lake include:
- Yuma Bat (Yuma Myotis)
- Little Brown Bat (Little Brown Myotis)
- California Bat (California Myotis)
- Silver-haired Bat
- Big Brown Bat
Occasionally, these bats have been observed:
- Hoary Bat
- Townsend's Big-eared Bat, which is on the state and federal Species
of Concern lists and which is considered one of the rarest mammal species
in the Northwest.
Visit Our Bats to see descriptions of each bat species, hear bat
calls, and learn about bat biology. A Night at Capitol Lake shares
the details of a typical summer’s night bat activity. Woodard
Bay talks about Washington’s largest bat colony, where visitors can
watch the female bats emerge at night and begin their long commute to
The Future of Capitol Lake Is in Question
Capitol Lake is a human creation in an area where the Deschutes River
meets Puget Sound. An intense and complex debate is currently going on
about the future of the lake. Input from the public will be sought
in March-May of 2009. At stake is whether the lake will remain,
whether it will be drained to create a tidal mudflat, or whether a combination
of the two options will be chosen.
The Problem of Pollution
The Deschutes River has been polluted for some time. Much of this
pollution has been captured in the Capitol Lake basin, which has not been
dredged recently. Whether water from the river flows first into
a lake or directly into Puget Sound, until the Deschutes River is cleaned
up, pollution will be brought into the area.
History of the Lake
Twenty-nine blocks of downtown Olympia and portions of the Port of Olympia
were created starting in 1909 by filling in the estuary of the Deschutes
River with landfill, and at the same time dredging out a portion of what
is now East Bay. Then in 1951 a dam was built by the current Fifth
Avenue Bridge, creating the 260-acre Capitol Lake from an area that used
to be a tidal mudflat. It is possible that this area may be returned,
in whole or in part, to a tidal mudflat by removing the dam. This
will partially recreate a portion of the former estuary within dramatically
(Click on the image to see a larger image)
This interpretive sign shows the former shoreline of Olympia and the
landfill. Fill is in light blue. The water features that exist
today are shown in dark blue. Note that the bottom of the map points
north. Only the northernmost part of Capitol Lake appears on the
map. For more on history, see the General Administration website’s history
of the lake.
current studies and deliberations provided by the working group charged
with choosing a preferred plan for the lake, see the Capitol
Lake Adaptive Management Plan.
A Washington State Department of Fish and Wildlife study examines
the impacts on wildlife of each of three alternatives: keeping Capitol
Lake as is, draining Capitol Lake to create a tidal mudflat estuary, or
a combination of the two. Several thousand species are diagramed showing
results for each option. Many species would gain from the change
to an estuary, such as salmon, other fish that swim in both salt and fresh
water, and a variety of birds (including surf scoters, goldeneyes, herons). Others
would lose from draining the lake, such as bats, freshwater fish, and
a different group of birds (including swifts, Purple Martins, swallows,
gadwall, wigeon, mergansers).
Impact on Bats of Draining Capitol Lake
The bats now feeding at Capitol Lake would be negatively impacted by
draining the lake and creating a tidal mudflat. The insects that
regularly hatch all summer from the lake have been a stable food source
for thousands of female bats living in Thurston County and for their growing
pups. Removing the food source will result in bat deaths—and no
one knows how many would die.
- Bats reproduce very slowly, a maximum of one pup a year for the Yuma
and Little Brown Bats. Once harmed, a bat population takes a long
time to rebuild.
- Bats live a long time, and form very stable patterns
of feeding. In 2008, a pregnant female Little Brown Bat was captured
and released near Roy, WA that had a band placed on her wrist in 1992.
She was caught near the same spot as in 1992, showing how stable the
association between a bat and a particular territory can be. We can
assume that many of the bats using Capitol Lake also have been visiting
the same section of the lake year after year, and may have great difficulty
in finding alternative feeding sites.
Position of Bats About Our Town Regarding Capitol Lake Alternatives
- Good water quality in Puget Sound is essential to the health of
our ecosystem. We support cost-effective projects that have a
good prospect of making favorable impacts on Puget Sound ecology. Our
members are currently divided on the question of whether restoring part
of the historic tidal mudflat would achieve those goals.
- The bats should be part of the discussion about alternative futures
for the lake.
- Any scenario for the future involves dredging the
lake. Do not dredge while the pregnant, then nursing, females are eating
at the lake—that is, do not dredge May through September.
the bats are still here, use their presence to educate the public about
bats—our mammalian cousins that are often feared and maligned.