Northern Leopard Frog. Rana pipiens

Description: Adult: A medium-sized frog with a head and body length of 50-100 mm. It is gracile, with a pointed snout, large and prominent eyes and a prominent tympanum that is about three-quarters the size of the eye. There are continuous, parallel dorsolateral folds that extend from behind the eye to the insertion of the hind limb. This fold is usually lighter than the background colour. The hind legs are elongate and the hind feet are strongly webbed. The background colour is greenish or brownish, punctuated with well-defined darker ovals or spots bordered with pale rings. These spots cover all but the venter, although the legs may be barred rather than spotted. There is a white stripe on the upper lip from the snout to the insertion of the forelimb. The belly is white or cream, with this colour extending part way up the flanks.

Larvae: Tadpoles hatch at about 8-10 mm total length and grow to a length of about 75 mm. The eyes of the tadpoles are dorsally placed, the dorsal fin moderately arched and slightly pigmented. Labial tooth rows 2/3. The froglets measure about 20 mm just after metamorphosis. The tadpoles are dark grey, olive or brown above, with fine gold flecks, and cream to white below. The ventral part of the abdomen is weakly pigmented. The anus is dextral and the spiracle sinistral.

Variation: The spotting typical of adults may be reduced or absent in froglets, and in rare instances, may result in a yellow morph. Males have enlarged, darkened nuptial pads during the breeding season. Males have paired vocal sacs over the forelimb insertions. Females are slightly larger than the males.

Natural history: This is the most cold-adapted of all leopard frogs. It inhabits springs, streams, marshes and other permanent water bodies, usually those with abundant aquatic vegetation. Streams are used for dispersal. Individuals may travel up to two kilometres in a single active season. It may forage far from water, but generally uses water as a safe refuge if threatened. It eats insects, spiders and other small invertebrates, but will also catbirds, garter snakes, tadpoles, small frogs and fish if given the opportunity and prey items of an appropriate size. Cannibalism has been reported. Tadpoles are preyed upon by larval tiger salamanders, the garter snakes Thamnophis elegans and T. sirtalis, and adults by snakes, small carnivores and birds. In winter it hibernates in the mud at the bottom of bodies of standing water or under rocks in streams and springs. The species is generally found in areas where the vegetation provides a good deal of ground cover. This species has survived up to nine years in captivity.

Reproduction: The leopard frog breeds from April to June and may enter into breeding behaviour while ice is still on the pond. For a given population the actual period of spawning activity may be somewhat reduced. Migration from sites of hibernation to preferred breeding sites may take place. Males call while floating in the water, the call being a long, low guttural rumble. In the breeding season, males are territorial. Amplexus is pectoral. Egg masses may be laid on vegetation or the pond bottom, and up to 6,000 may be deposited by a single female. The eggs are about 1.7 mm in diameter and generally require from ten days to three weeks to hatch, depending upon water temperature. After metamorphosis individuals take from two to three years to become sexually mature.

Voice: A mixed repertoire of low frequency sounds that may be described as "grunts," "chuckles" and "snores." A higher pitched release scream may be emitted when handled. Both sexes can croak, but females rarely do and the voice is weak.

Distribution: In Alberta, the leopard frog occurs from the Montana border north and west to the Little Smoky River area. Locality records exist as far north as the Slave River, but the true distribution north of about 55° N is poorly known. The western extent of the range is in the foothills and lower elevations of the Rockies. It is distributed extensively in regions of short-grass prairie, as well as aspen parkland and boreal forest. It also occurs in the Cypress Hills.

On the accompanying range map, solid circles represent populations occurring within the current range of this species. Solid squares represent pre-1981 reports that lie outside of the present range and probably depict extirpated populations. Extralimitally, it is broadly distributed from south central Northwest Territories to California in the west, extreme southern New Mexico in the south, through the northern plains states, east through the Ohio Valley to New England, Quebec and the Maritime provinces.

Conservation status: The range of the northern leopard frog has contracted greatly over the last several decades. A variety of causes, perhaps including disease, have wiped out populations everywhere except the southeastern (and probably the extreme northeastern) corner of the province, where relatively few breeding populations remain. These populations, however, appear to be recovering and although still in jeopardy the status of this species in Alberta appears to be improving. Extensive monitoring by Alberta Fish and Wildlife has probably contributed significantly

to the arrest of its decline.

Remarks: Rana pipiens is part of a large complex of very similar leopard frogs that range across all of North America. The abundance of Rana pipiens in Alberta appears to have declined markedly since 1978. It is not known why this decline has taken place, but there is some speculation that it may be due to the effects of herbicides and pesticides. Several consecutive drought years may also have had an effect, destroying some breeding sites and resulting in overwinter freezing deaths of adults. It has been widely used in laboratory studies.

Significant references: Black 1969; Briggs 1949; Browder and Davison 1964; Cunjak 1986; de Benedictis 1974; Di Berrardino 1962; Emery et al. 1972; Gilbert et al. 1994; Greenwald 1971; Hunter et al. 1989; Klassen 1991; Layne, 1992; Licht 1991; McClelland and Wilczynski 1989; Moore 1949; Mosimann and Rabb 1952; Post and Pettus 1966; Roberts 1981, 1992; Ruibal 1959, 1962a; Sage and Selander 1979; Schueler 1982b; Scott and Jennings 1985; Seburn et al. 1997; Shivers and James 1970; Shumway 1940; Smith et al. 1988; Smithberg 1954; Taylor and Kollross 1946; Verma 1965; Wagner 1997; Yaremko 1994.