Anaxyrus microscaphus

Anaxyrus microscaphus: The Arizona Toad

The Arizona toad, scientifically known as Anaxyrus microscaphus, is a species of toad indigenous to the southwestern United States. Its natural range encompasses parts of Arizona, New Mexico, Nevada, and Utah, where it inhabits a diverse array of temperate environments. These include lowland forests, riparian zones along rivers and streams, swamps, freshwater marshes, and springs. The species is also found in man-made habitats such as open excavations, irrigated fields, and seasonally flooded agricultural lands.

Description and Identification

Adult Arizona toads typically measure between 53 and 79 millimeters in snout-to-vent length. Their dorsal coloration is highly variable, commonly presenting as gray or beige, often adorned with distinct reddish-brown warts. A notable characteristic is the presence of oval parotoid glands, which are widely separated. Many individuals also exhibit a pale stripe or patch on their head or along their spine. Juvenile toads often display a more vibrant salmon color or a greenish-brown hue.

Habitat and Distribution

The Arizona toad's distribution is notably continuous along the Virgin River and its tributaries in southwestern Utah and southern Nevada, extending into various locations across Arizona and western New Mexico. They are considered a protected species in Utah, Nevada, and Arizona, with protected populations established within Zion National Park. These toads prefer sandy substrates situated within approximately 100 meters of water sources, frequently in areas with flood channels and dense stands of willows. They also occupy nearby sandy terraces populated by live oaks and cottonwoods. During the summer rainy periods, they may be found at higher altitudes, up to about 2,000 meters, within forested riparian corridors. After the breeding season, they often move into irrigated fields and are found around reservoirs and other impounded water bodies.

Behavior and Reproduction

Arizona toads are primarily nocturnal, seeking refuge in sandy burrows during daylight hours. They enter a state of torpor and remain underground from roughly September through February. Breeding activities commence in backwaters and along the edges of streams and side-pools. The breeding season begins in late February in Arizona and continues several weeks later at higher elevations and in Utah. Males attract females with a distinctive trilling call that lasts about six seconds, though satellite males often play a role in opportunistic mating. Following amplexus, females deposit clutches of approximately 4,500 eggs in shallow water. The eggs typically hatch within three to six days, with tadpole development time being significantly influenced by water temperature. The diet of adult toads has not been extensively studied, but their tadpoles are believed to feed on algae and other organisms found on submerged surfaces.

Conservation Status and Threats

The population of the Arizona toad is believed to be experiencing a slow rate of decline, likely attributed to human disturbance of their habitats. In certain areas, such as central Arizona, they are being displaced by Woodhouse's toad (Anaxyrus woodhousii). Hybridization between these two species poses a significant threat. While they occupy similar habitats, theoretical reproductive isolation exists due to different breeding seasons. However, instances of male Arizona toads mating with female Woodhouse's toads have been observed. The Arizona toad has also been known to attempt interspecific mating with several other species, including the Great Basin spadefoot toad, the Great Plains toad, the red-spotted toad, the canyon tree frog, the American bullfrog, and the lowland leopard frog. Despite these threats, the Arizona toad possesses a wide range and is assumed to have a substantial total population. Its adaptability to some degree of habitat modification has led the International Union for Conservation of Nature to classify its conservation status as 'Least Concern'.