A frog introduced for hunting and food has become a threat to one of Arizona’s native snakes. Fish and Wildlife Service species assessment traces bullfrogs’ arrival in Arizona to 1926, following a systematic introduction effort by the State Game Department to provide opportunities for sport hunting and a source of food. The assessment identifies nonnative species, particularly bullfrogs, crayfish, and sport fish, as major threats to the northern Mexican garter snake, which the document estimates occupies only about 10% of its historical habitat.
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Slow reproduction may make recovery harder. About half of sexually mature females in a population may reproduce in a given season. Bullfrogs can also disperse over land and recolonize nearby water bodies, making continued monitoring important. Alex Koeberle describes this challenge in a Fish and Wildlife Service case study published through the Conservation and Adaptation Resources Toolbox.
The Fish and Wildlife Service assessment reports that female northern Mexican garter snakes give birth to between seven and 38 young, averaging 13.6.
Its longer-term benefit would depend on the survival of the introduced frogs, the snakes’ ability to use the additional prey, and whether bullfrogs returned to the area. In Scotia Canyon, conservation teams have worked to control invasive bullfrogs and restore populations of Chiricahua leopard frogs, a native prey species. Before these efforts, informal surveys over eight years had recorded just one adult northern Mexican garter snake. The intervention was intended to restore a native food source for the snakes.
In fall 2009, hundreds of leopard frog tadpoles and young frogs were introduced to the site.
