Canadian Toad. Bufo hemiophrys

Description: Adult: A small toad, reaching a head and body length of 37-75 mm. It has a short body and a skin covered with small, irregular warts. The parotids are large and oval or kidney-shaped. The interorbital region bears a large, solid boss that may be flat, convex or slightly furrowed. Tympanum smaller than eye. Toes of hind feet feebly webbed. Two prominent, dark-coloured tubercles on the hind feet, the inner one large and the outer one small. Background colour generally grey-green or brown, with reddish tubercles encompassed by dark spots. Typically with a whitish vertebral stripe (not as contrasting with the background colour as that of Bufo boreas). Belly white, spotted with grey, becoming pale yellowish laterally.

Larvae: The tadpoles are blackish above and lighter below, with a transparent region in the anterior part of the venter. The tail musculature is dark and the caudal fin is slightly pigmented. The labial teeth are 2/3. The spiracle is sinistral, the anus medial.

Variation: Toadlets have weakly developed cranial crests that become accentuated and fuse with age to form the adult boss. Males with

a dark throat. In females, the throat is the same colour as the belly. Males have a single, rounded vocal sac.

Natural history: In Alberta, active from April until September. It is usually diurnal and burrows at night, although it may also be nocturnally active if the temperature is high enough. In high temperatures it seeks shade. When threatened Canadian toads may swim far from shore to seek protection. Four species of helminth parasite have been recorded, with an incidence of eighteen to seventy-three percent.

Reproduction: Breeding occurs from May to July. Males may be active and call at temperatures as low as 5°C. Breeding usually takes place in the shallows of lakes, ponds, ditches, marshes and other temporary bodies of water. Amplexus is pectoral. A long, single string of eggs of 1.0 mm diameter is laid.

Voice: A short (1-5 seconds), soft trill repeated after intervals of about thirty seconds.

Distribution: In Alberta, this species occurs from north and east of the Bow River to the Northwest Territories border. It is confined essentially to the eastern half of the province. There is extensive overlap with Bufo boreas to the west and north of Edmonton. Scattered records exist that indicate that this species extends into the foothills of the Rockies, but these may be doubtful. It occurs at elevations of up to 1,200 m, primarily in boreal forest and aspen parkland, with some records from the short-grass prairie.

Extralimitally, it occurs from the southern Northwest Territories through all of Saskatchewan, except the extreme north east corner, to south central Manitoba, western Minnesota, north east South Dakota and northern North Dakota and Montana. Isolated populations previously reported to exist in southeastern Wyoming have now been recognized as a full species, B. baxteri. In southeastern Manitoba B. hemiophrys hybridizes with B. americanus, producing fertile off- spring in the ecotone between prairie and forest. Some authors accept this as evidence that B. hemiophrys should be considered as a subspecies of B. americanus.

Conservation status: This species has declined in recent years, especially in the more heavily populated areas of the province, apparently as a result of the destruction of appropriate wetland habitat. A volunteer monitoring program that operated largely in the southern part of the province yielded no positive reports of this species, indicating that the decline may be both continuing and truly alarming.

Remarks: In Elk Island National Park, the numbers of this species declined significantly from 1971 to the mid-1980s. This trend is consistent with that for this species in central Alberta as a whole. Adults emerge in the spring earlier than immatures, but both sexes in each age class emerge at about the same time. In conditions of high ambient temperatures, individuals move into the shade. In Minnesota, this species has been observed to burrow at the onset of winter in such a way as to keep ahead of the frost line, and follow it back up for spring emergence. Large numbers of toads may over- winter in communal sites. Two subspecies are recognized. That occurring in Alberta is Bufo hemiophrys hemiophrys. Amplexus has been observed in Alberta between this species and Bufo boreas.

Significant references: Black 1970a, 1971; Blair 1957; Breckenridge and Tester 1961, 1964; Burns (no date); Bursey and Goldberg, 1998; Clarke 1974; Cook 1964b, 1983e; Eaton et al. 1999; Green 1983; Hamilton et al. 1996; Hamilton et al. 1998; Henrich 1968; Kelleher and Tester 1969; Kuyt 1991; Powell et al. 1996; Roberts, 1992; Roberts and Lewin 1979; Sanders, 1987; Smith et al. 1998; Tester and Breckenridge 1964; Tester et al. 1965; Turner et al. 1965; Underhill 1961.