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Photo by Breck Bartholomew
Photo Copyright Breck Bartholomew
Arizona Toad
Anaxyrus microscaphus
NatureServe conservation status
Global (G-rank): G4
State (S-rank): S2
External links
Species range
This species occurs in southern Utah in Washington, Kane, and San Juan counties.
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).
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). W. R. Bosworth and G. V. Oliver 2003)
