Alberta Inventory for the Northern Leopard Frog 2000/2001
Author(s)
Kris Kendell
Summary
The northern leopard frog (Rana pipiens) was once a widespread species found throughout much of southern and centeal Alberta. In the late 1970s, the leopard frog exhibited a dramatic decline in distribution and numbers throughout much of its historic range in Alberta. Today, the leopard frog is designated as "Threatened" under Alberta's Wildlife Act. The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) lists the prairie population of Rana pipiens as "Special Concern" (COSEWIC 2001).
Since 1990, no province-wide survey has been conducted to assess disctribution and status of extant populations of the leopard frog in Alberta. A two-year inventory project was initiated in 2000 and completed in 2001 to collect information on the current status of the leopard frog in the province and to determine possible changes in population numbers and distribution. In total, 297 leopard frog sites were compiled for investigation These sites were obtained from record information held in the Alberta Fish and Wildlife Division, Biodiversity Species Observation Database (BSOD).
To help increase the efficiency and maximize survey efforts for leopard frogs, a survey protocol was drafted in the spring of 2000 and subsequently revised in 2002. The protocol recommended the use of call surveys and an area search technique (visual encounter survey) as the primary survey method for leopard frogs. However, call surveys were employed on a very limited baseis in the spring because of time constraints and were subsequently abandoned for more efficient visual encounter surveys later in the summer. Surveys were conducted in potentially suitable frog habitat to maximize the chance of observation and targeted in the late summer to correspond with the emergence of young-of-the-year frogs. The late summer surveys also provided an added benefit of identifying waterbodies used for breeding and determining the successful development eggs and metamorphosis of tadpoles.
In total, 269 sites were investigated for the northern leopard frog in 2000 and 2001 and frogs were found at 54 of these sites. The majority of the leopard frog observations were associated with major river drainages including the lower Red Deer River, the Oldman River, the South Saskatchewan River, lower Bow River and the Milk River. Leopard frogs were also observed in the Cypress Hills region, Willow Creek drainage (west of Stavely) and in the extreme northeast region of Alberta.
Presence data at surveyed sites in 2000-2001 was compared to survey results from a provincial leopard from a provincial leopard frog inventory conducted by Sweet Grass Consultants Ltd. in 1990 (Wershler 1991). Results in 2000-2001 indicate that the northern leopard frog has experienced additional local extirpations over the last decade from four occupied sites that were surveyed in 1990. Findings from the 2000-2001 inventory also suggest that the species has not re-colonized formerly occupied parts of its range since its dramatic decline in the 1970s. In addition, many of the existing leopard frog sites ramina fragmented and isolated. This, in-conjunction with the low recolonization potential of the leopard frog, may result in further local loss of populations if these sites experience disease, disturbance or catastrophic events such as winter mortality caused by anoxic conditions or loss of breeding habitat over consecutive years because of drought.