Amidst the symphony of sounds emitted from a shallow pond on a spring or summer night, a listener may not realize the social interactions taking place at the water's edge. Male toads and frogs gather at breeding sites and announce their presence with what is known as advertisement calls. When one male calls, others soon call back in contest, creating a rising chorus that falls slowly silent.
Each of Minnesota’s 14 species has a distinct call used to attract females of the species. Although an individual species tends to breed at the same time each year, fluctuations in weather can cause variations. Wood frogs breed early in the spring, taking advantage of temporary wetlands. They are called explosive breeders, meaning they gather in large numbers, but only for a few days. Prolonged breeders, such as gray treefrogs, can be heard calling for several weeks. Other calls produced by toads and frogs include aggressive calls made by a male when another male enters his breeding territory, and rain calls made after the breeding season and may be related to changes in the weather.
|Species||Early March||Late March||Early April||Late April||Early May||Late May||Early June||Late June||Early July||Late July|
|Boreal Chorus Frog||X||X||X|
|Northern Leopard Frog||X||X||X|
|Great Plains Toad||X||X|
|Cope's Gray Treefrog||X||X||X|
|Northern Cricket Frog||X||X||X|
As males congregate and call at the breeding pond, the larger more aggressive males are able to defend the best egg-laying sites and will attract the most females. Females respond to the calling males by moving around a breeding pool, going near several males before selecting one to breed with. The older, larger males can often be identified by a deeper or faster call. The female will sit near and sometimes touch the male to indicate her interest. The male climbs onto the female, which then swims with the attached mate to a location within the male's breeding territory and begins laying eggs. Males may cling to the females for several hours in amplexus, externally fertilizing the eggs as they are laid.
The mating tactics of individual species tend to vary depending on whether they are explosive or prolonged breeders. In explosive breeders, males will often abandon calling temporarily to swim after and grab frogs moving nearby in hopes of intercepting receptive females. In many prolonged breeders, males will establish territories and defend these prime calling sites from other males. Dominant males that claim preferred breeding sites attract more females. Satellite males, which are often smaller, quietly wait nearby to intercept an approaching female. In some species, satellite males may steal the perch of a dominant male that leaves to breed with a receptive female.