Mazatlan Narrow-mouthed Toad (Gastrophryne mazatlanensis)
Mazatlan Narrow-mouthed Toad near Huasabas, Sonora. Photo by Jim Rorabaugh
Editor’s Note: Western populations of Gastrophryne olivacea, including those in Arizona and Sonora, have recently been elevated to species status, and are now known as the Mazatlan Narrow-mouthed Toad, G. mazatlanensis.
One of Arizona’s smallest amphibians, the Great Plains Narrow-Mouthed Toad rarely reaches 4 cm. (1 5/8 in.). Smooth, wartless skin, plump shape with short limbs, narrow, pointed head and a fold of loose skin behind the eyes help make this one of Arizona’s most distinctive amphibians. Color dorsally ranges from light gray to light brown, with indiscriminant black spotting with occasional mottling along the legs. Faint spots of white can also be present. Sexually mature males have dark throat patch and vocal sac.
Occurs in three distinct habitat types; Madrean evergreen woodland, semi-desert grassland, and Sonoran Desert scrub. Found from Santa Cruz Co, north to Maricopa Co. and west to near Ajo in western Pima Co. Sympatric with Smilisca fodiens and Anaxyrus retiformis throughout much of its range in Arizona.
Secretive and difficult to locate, during even the largest of breeding choruses, this nocturnal, diminutive toad-like amphibian rarely strays from the protection of cover. During its breeding season it frequently calls from deep within the snags and snarls of mesquite bosques that provide an impenetrable protective armor against most predators.
One of the many monsoonal breeders in Arizona, its call can often be confused with Anaxyrus retiformis. The mating call is a high pitched buzz that lasts about 3 1/2 seconds and ends abruptly. The call is best described as the high pitched bleating of sheep. From a close distance, a hitch, or “click” can be heard at the start of the call. Tadpoles have a characteristic habit of floating motionlessly at the waters’ surface.
The relative abundance of this species in Arizona is poorly known. Recent observations indicate this amphibian may be expanding its range. However, this conclusion is tentative due to the small size, secretive habits and the lack of a thorough distributional study.
When handled this annuran exudes a potent toxin that can cause severe nasal reactions and burning of the eyes. The toxin appears to kill other amphibians and may be a protective mechanism.
In Arizona, the Great Plains Narrow-Mouthed Toad (Gastrophryne olivecea) is found. Currently no subspecies are recognized in Arizona.
Author: Erik F. Enderson. Originally published in the Sonoran Herpetologist 15 (7) 2002.
For additional information on this species, please see the following volume and pages in the Sonoran Herpetologist: 2005 Jul:74-78.