Butler's Garter snake Conservation in Wisconsin
The Butler’s
garter snake (Thamnophis butleri) is a threatened species in the state
of Wisconsin, protected under the state’s Endangered Species Act. Very
few studies have been conducted on this species, and little is known
about its ecology and life history in Wisconsin. Wisconsin’s T.
butleri population exists as scattered, probably isolated,
subpopulations. T. butleri subpopulations in Wisconsin are centered on
wetland hibernacula, and finding individuals outside of these localized
populations is quite rare. Where present, however, this species often
exists at high densities, and it can outnumber populations of other
coexisting snake species.
T. butleri displays a strong
affinity for the edges of the wetlands in which it hibernates, often in
burrows of the prairie crayfish (Procambaris gracilis). However, T.
butleri can also range into seasonally dry upland habitat as long as
standing water and dense moist grass are available nearby. These life
history traits of T. butleri may prevent individuals from dispersing
away from a deteriorating habitat,. In addition, development in
Wisconsin has separated most T. butleri populations by roads, where
dispersing snakes typically experience high roadside mortality rates.
Furthermore, T. butleri shows a behavioral avoidance of roads.
The
most important threat to T. butleri is the rapid loss of wetlands and
adjacent habitats through development. Because of the current building
boom in southeastern Wisconsin, developers are increasing interested in
building on lands adjacent to wetlands, which could impact T. butleri
habitat. This desire to develop wetland sites occupied by T. butleri
has led to a clash between conservation agencies and developers and
forced numerous construction delays and reconfigurations.
Current
state regulations adequately protect wetland areas, but the adjacent
uplands remain unprotected unless they are occupied by T. butleri. A
central issue in protecting upland habitat for T. butleri is how far
individuals range from a wetland edge. In this study we addressed the
critical lack of knowledge regarding the extent of T. butleri’s use of
upland habitats adjacent to wetland hibernacula. We found that 25% of
329 observations of T. butleri were within 63 feet (19m) of a wetland
edge; 50% within 138 feet (42m), and 75% within 238 feet (72m). Our
results increased management effectiveness by basing buffer zone
regulations upon scientific evidence. We also examined the seasonal
aspect of upland habitat use by T. butleri in order to define the
periods when snakes are active and vulnerable to incidental take by
construction activities.
Collaborators:
Stan Temple
Jeff Lorch
Bob Hay
Gary Casper