Over the last 35 years, Northern Leopard Frog (Rana piplens) populations have declined dramatically over much of the species' range in North America. Abrupt population declines were first noted in Alberta in 1979. Since then, populations appear to have been extirpated over much of central Alberta and are absent or greatly reduced in southern Alberta. Only a handful of viable breeding populations currently remain in southeastern Alberta. Because of its virtual disappearance from the province, the Northern Leopard Frog has been designated as an endangered species under the Alberta Wildlife Act.
The Northern Leopard Frog requires a mosaic of habitat types to meet the annual requirements of all life history stages. Generally, separate sites are used for breeding and overwintering. However, in some cases breeding and overwintering may occur in the same pond. This is particularly true in spring fed wetlands. In Alberta, Northern Leopard Frogs are typically associated with clear water that is relatively fresh to moderately saline. Other parameters of water quality, however, vary widely between sites.
Breeding occurs in shallow and warm standing water associated with permanent and semi-permanent wetlands, springs, dugouts, borrow pits, lakes, beaver ponds, and the backwaters and oxbows of rivers. Temporary ponds and shallow lakes that are unsuitable for fish, and that contain water until late July or August are considered to be the most favourable spawning sites for Northern Leopard Frogs. Most breeding ponds contain a mixture of open water and emergent vegetation. Although at some sites in Alberta, breeding ponds are totally encompassed by emergent vegetation. Leopard Frog tadpoles are generally poorly adapted to cope with currents and thus can develop successfully only in slow reaches of streams or backwaters.
Unlike most of Alberta's other species of amphibians, Northern Leopard Frogs overwinter in water. Overwintering frogs require well-oxygenated water that does not freeze to the bottom during the winter. Hibernacula are most often located in springs, streams, spillways below dams, or in deeper lakes and ponds. Frogs have been found hibernating under rocks, logs, leaf litter or vegetation, or in depressions in sand or mud. Shallow breeding ponds and lakes are unsuitable for overwintering because of the depletion of oxygen in the water column, which can lead to winterkill. In southern Alberta, springs appear to provide critical overwintering habitat during periods of drought when deeper permanent water sources become limited.