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Photo by Breck Bartholomew
Photo Copyright Breck Bartholomew
Arizona Toad
Anaxyrus microscaphus
NatureServe conservation status
Global (G-rank): G3G4
State (S-rank): S3
- Reason: This species has a limited and discontinuous distribution; it reaches the northern limit of its range in extreme southern Utah. Though locally common in some places Utah, it is restricted to the southwestern part of the state, mainly in Washington and Kane counties. Habitat modification leading to hybridization with another species of toad is known to be a threat to this species in Utah.
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General information
The Arizona toad, Bufo microscaphus, occurs in isolated areas of the southwestern United States. In Utah, the Arizona toad is found only in the southwestern portion of the state. This species inhabits streams, washes, irrigated crop lands, reservoirs, and uplands adjacent to water. It is inactive in cold weather, and adults are mainly nocturnal, whereas the newly metamorphosed young are active during daylight hours.
The Arizona toad lays eggs on the bottoms of shallow, slow-moving streams. The diet of adults consists mainly of insects and snails, whereas larvae (tadpoles) consume plant matter and organic debris. Adults are typically 2-31/4" long, and range in color from greenish gray to brown, with a light-colored stripe across the head.
Phenology
These toads are inactive in cold temperatures. Adults are primarily nocturnal except during the breeding season (Stebbins 1985). Adults are active at ambient temperatures of about 22-35 C. Newly metamorphosed individuals often are active during daylight hours.
Species range
This species occurs in southern Utah in Washington, Kane, and San Juan counties.
Migration
Individuals may migrate short distances between nonbreeding terrestrial habitats and breeding pools.
Habitat
Schwinn and Minden (1980) listed the breeding habitats of this species in Utah as aquatic habitats and riparian habitats, and the nonbreeding habitats as additionally including "[i]ntermittent or temporary plains streams, mountain tributaries, rain pools, marshes, ponds, stock tanks and ponds or irrigation ditches", "[s]pring-fed seeps and small creeks with permanent flow", "open water zones or permanent lakes, reervoirs or ponds", "[m]arshes, wetlands, swampy river bottoms or lake and reservoir shorelines where rooted aquatic plants occur", and "[p]ermanent streams or rivers in broad valleys and plains with low gradient and silt, sand or gravel bottoms". Dahl et al. (2000) described a breeding site in Utah that was "a narrow (1-3 m width), shallow, intermittent stream (<0.5 m in depth at its deepest point)." They also reported: "In many places stream banks rise 3-4 m above the flow. The streambed consists of various mixtures of sandy soil and rock, and stream bank vegetation ranges from sparse shrubs and grasses to thick shrubs and trees with large, branching canopies." Oliver (personal observations) has found this species in Utah in areas dominated by junipers, in stream beds with cottonwoods, and along streams with willows.
Food habits
Tanner (1931) listed stomach contents of five individuals of this species (as "BUFO COMPACTILIS") from Zion National Park; four stomachs contained beetles (of four families: Carabidae, Elateridae, Tenebrionidae, and Staphylinidae), three stomachs contained ants, one stomach each contained a Jerusalem or sand cricket, a moth larva, a honey bee, a bug (Pentatomidae), and two mountainsnails. Two stomachs contained plant fragments, probably ingested unintentionally. It is of interest that many of the prey items are either known to be noxious (the honey bee) or are members of taxonomic groups known to contain mostly noxious species (Carabidae, Tenebrionidae, and Pentatomidae).
Reproductive characteristics
In west-central Arizona, breeding occurred February-April, independent of rainfall, and usually occurred for a total of a few weeks each year (Sullivan 1992). In southwestern Utah, breeding peaks in June. At higher elevations, breeding may extend to July or perhaps August (Stebbins 1985).
Threats or limiting factors
Habitat loss, particularly water withdrawal, is an important threat to many populations. In some areas, population decline has evidently resulted from habitat alteration and interactions with Woodhouse's toad (Bufo woodhousii). Price and Sullivan (1988) wrote: "B. woodhousii generally utilizes lentic aquatic sites for breeding and avoids the lotic habitats frequented by microscaphus. Human alteration, however, apparently has allowed B. woodhousii access to habitats previously occupied solely by microscaphus there are indications that B. woodhousii is replacing B. microscaphus in some drainages." Conversion of lotic aquatic sites to lentic situations in Utah not only allows B. woodhousii to supplant B. microscaphus but also brings the two together at breeding sites. Of importance is that B. microscaphus readily hybridizes with Woodhouse's toad, which has resulted in the genetic swamping of some populations (Blair 1955).
References
- Biotics Database. 2005. Utah Division of Wildlife Resources, NatureServe, and the network of Natural Heritage Programs and Conservation Data Centers.
- Stebbins, R. C. 1985. A field guide to western reptiles and amphibians. Houghton Mifflin Company, Boston. 336 pp.
