The wood frog (Rana sylvatica) is one of few amphibian species in Rocky Mountain
National Park
and is the only remaining member of the amphibian family Ranidae ("true frogs") to inhabit the
Park. The Front Range of Colorado, including Rocky Mountain National Park, has
experienced unexplained declines and extirpations of another, formerly common
member of this family, the leopard frog (Rana pipiens). While many sections along
the Front Range have undergone suburban development and other human-induced
alterations, the Park is relatively undisturbed,
making the absence of leopard frogs even more puzzling. The wood frog was recently
removed from Colorado's list of threatened species but remains an amphibian of concern
and interest for two reasons: 1) it is one of only three anuran (frogs and toads)
species that occur in Rocky Mountain National Park and 2) it has been
diagnosed with chytrid fungus, but may not be lethally affected by this disease.
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The wood frogs in Colorado and Wyoming represent a disjunct
portion of the total range over which the species occurs. It is
found in many parts of North America, including areas north of
the Arctic Circle in Alaska. Its range dips down as far south as
Alabama (in the mountains) in the east, though it typically occurs
in more northerly locations. Wood frogs require natural, semipermanent
or temporary pools and adjacent wet meadows. The
frogs are most conspicuous very early in the spring when they
congregate at breeding sites. Snow and ice are often present
along the margins of the ponds at this time. Wood frogs may
disperse into surrounding marshes and woodlands soon after
breeding and laying eggs, though little is known about their
movements. In early fall, they begin to seek places to hibernate
(hibernacula), such as in shallow depressions under leaf litter. A
special characteristic of wood frogs is that they are freeze-tolerant,
allowing them to survive temperatures well below freezing. [To
learn more about freeze tolerance in frogs, visit web sites
such as provided by Manitoba's NatureNorth,
the California Academy of Sciences,
and the Environmental News Network]
Most information available for wood frogs has focused on eastern
populations and habitats. We have been monitoring one population
of wood frogs in Rocky Mountain National Park for two years, a
project that will continue long-term and will provide us with an
opportunity to conduct research to answer questions associated
with small populations in western montane environments.
Recently, we identified the presence of chytrid fungus in frogs on
the west side of the Park. This disease has been linked to
amphibian declines in Australia, Central America, and the Rocky
Mountains, though its effects on wood frogs are unknown.
We are using a variety of techniques to monitor this apparently
healthy population of wood frogs, including automated frog calling
recorders, capture-recapture techniques, and radio telemetry.
Over time, we will estimate the number of individual male frogs in
this population, document timing and success of reproduction, and
investigate when and where movements occur during and after
the breeding season. Information about wood frog movements
between breeding sites and to and from hibernacula can be
important to Park managers in their efforts to maintain adequate
habitat and resources for a healthy population of wood frogs. This
long-term project will improve our understanding of the importance
of environmental factors such as water levels, pond drying dates,
and snowpack depths, durations, and temperatures on wood frogs
and on other amphibian populations.
[Click here to learn more
about USGS ARMI research being conducted in the Rocky Mountains]
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Distribution (in green) of the wood
frog in the conterminous United
States. (Click on photo to enlarge)
A pond used for breeding by wood
frogs in Rocky Mountain National Park.(Click on photo to enlarge)
Radio telemetry is used for tracking the movements of individual frogs. This photo shows a wood frog equipped with a radio assembly.
(Click on photo to enlarge)
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