Great Plains Toad. Bufo cognatus

Description: Adult: A moderately large toad, with a head and body length of 45-110 mm. Parotids large, oval. Cranial crests form an "L" around each eye and fuse anteriorly to form a boss. Tympanum smaller than eye. Skin covered with small warts. Toes of hind feet weakly webbed. Hind feet with sharp-edged tubercles on the ventral surface. Background colour pale brown-grey or olive, with an irregular pattern of darker blotches, some of which may have even darker borders. A vertebral stripe may be present. Venter immaculate white.

Larvae: Tadpoles reach about 25 mm total length. Labial teeth 2/3. Dorsal fin arched. Anus median, spiracle sinistral. Mottled brown and grey or blackish dorsally, light green below. The venter may be iridescent.

Variation: Toadlets with many small reddish tubercles and cranial crests forming a' V.' Males have a single, elongate vocal sac, equivalent to about one third of the body volume when inflated.

Natural history: Active in Alberta from April until September. Generally nocturnal in its activity patterns. A good burrower that spends much of its time underground. When exposed to high temperatures it burrows. It frequents irrigation canals, river flood plains, temporary rain pools and dugouts. If threatened the great plains toad inflates itself with air, depresses its head and stands high on all four legs. It is known to eat moths, flies and beetles.

Reproduction: Breeding takes place after rains in spring or summer, and occurs in temporary ponds, dugouts, ditches, flooded fields, marshes or streams. Breeding takes place in clear, shallow water and this species will not breed in muddy water. Amplexus is pectoral. Female may produce a clutch of 20,000 eggs. The eggs are produced in long strings, hatch in about two days, and the tadpoles metamorphose in about six weeks. Tadpoles naturally aggregate, possibly as a defensive strategy. It may be diurnal during the breeding period. Sexual maturity is attained in three to five years.

Voice: A repeated, harsh clatter of great intensity and long duration (up to 50 seconds). Males also produce a release call if molested. Females are basically voiceless. The type of water habitat, perma- nent or temporary, may play a role in determining the intensity

of the chorus.

Distribution: In Alberta, limited to the extreme southeastern corner of the province, south of the Red Deer River and east of a line connecting Brooks, Vauxhall and Taber. Most localities are in the vicinity of the South Saskatchewan River and its tributaries. Restricted to short-grass prairie habitats. Occurs at elevations up to 900 m. Extralimitally, it occurs from southwestern Saskatchewan through central Montana, south through the plains states to San Luis Potosi, Mexico. Also from central Utah and the Colorado River south into western Mexico. Several additional isolated populations exist.

Conservation status: This species has experienced population declines since the 1980s. This appears to be due to habitat loss (largely through agriculture) and drought.

Remarks: This species is known to be active at a range of temperatures normally not tolerated by other members of the genus Bufo. This is particularly significant for activity at the relatively high ambient temperatures encountered by Bufo cognatus when compared to those encountered by its relatives in the province.

Significant references: Bieniak and Watka 1962; Black 1971a; Blair 1963; Bragg 1936, 1940; Brown and Pierce 1967; Clark and Chandler, 1991; Clarke 1974; Flowers and Graves 1995; Graves et al. 1993; James 1998a; Logier 1931; Moore 1953b; Roberts, 1992; Rogers 1973; Ruibal 1962b; Sanders, 1987; Smith 1946; Tester et al. 1965; Turner et al. 1965.