Description
The Bullfrog is the largest frog found in North America. Their
tadpoles also grow larger than other species. The colour varies from pale
green to dark greenish/brown above and is creamy white below with variable
dark mottling on the back or underside. It is distinguished by its very
large tympanum which is always larger than the
eye, and by the lack of dorsolateral ridges.
Adult males have pale to bright yellow chins during the breeding season.
Adults may reach up to 17 cm long.
Call
The call of the Bullfrog is deep and resonant, often described
as a bass, growly "jug-o-rum". A full chorus can be heard half
a kilometre away.
Confusing Species
Subadult Bullfrogs can sometimes be confused with Green
Frogs, however Green Frogs have two dorsolateral ridges that run partway
down the back. An adult male Green Frog also has a large tympanum and yellow
breeding colours, but is much smaller than an adult male Bullfrog.
Distribution
Bullfrogs are native to the deciduous forest zones of Ontario,
Quebec, New Brunswick and Nova Scotia. It is introduced to British Columbia
where it has spread along the lower mainland and Vancouver Island. It is
naturally found through much of the eastern and central United States and
has been introduced to numerous locations in the west and well as elsewhere
in the world.
Habitat
Bullfrogs require large permanent water bodies to breed but
may spend part of the summer in smaller ponds. They are usually found in
water along a well vegetated shoreline.
Reproduction
Breeding is later than in most other frogs and usually occurs
from mid-June to late July on warm, humid or rainy nights. Egg masses may
contain up to 20,000 eggs and spread out over the surface of the water
when they are first laid. Tadpoles grow for up to three years before transforming
into frogs.
Natural history
Male bullfrogs reach maturity about three years after transforming
while females may take five or more years to mature. In the wild, they
are known to live up to nine years after transforming. Bullfrogs are known
for their voracious appetite and smaller frogs (including other Bullfrogs!)
make up an important part of their diet along with insects, small mammals
and even occasionally small birds. In winter Bullfrogs hibernate in large,
deep ponds, lakes and rivers.
Conservation Concerns
There is a problem with too few Bullfrogs in some parts of their
range, such as eastern Ontario, and too many in other parts such as British
Columbia where they have been introduced. Many people harvest Bullfrogs
for frogs' legs either commercially or for their own use. This is now prohibited
in some areas. Harvesting of large frogs for food has lead to a decline
in several species around the world and Bullfrogs are no exception. The
importance of Bullfrogs for human food has also lead them to be introduced
to many areas where they are not native. Because Bullfrogs eat smaller
frogs they may contribute to declines in some other species which are not
adapted to their presence.
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