Published: October 1999
Author(s): Kelly R. McAllister, William P. Leonard, David W. Hays and Ronald C. Friesz
The northern leopard frog is one of the most widely distributed amphibians in North America. Recently, however, declines in the populations of this species have been reported from throughout North America, including the Pacific Northwest. In Washington, museum records indicate that the leopard frog inhabited at least 18 general areas in eastern Washington, many of these along the Columbia River and its major tributaries.
The northern leopard frog has been called the "meadow frog" for its summertime movements away from natal ponds. They may range widely into a wide variety of habitats, even hay fields and grassy woodlands, but apparently require a high degree of vegetative cover for concealment. Leopard frogs require permanent deep water for overwintering, in proximity to seasonal ponds and wetlands for breeding. Tadpoles feed on algae, rotting vegetation, and detritus. Adult frogs feed primarily on insects, but will also eat other frogs (including small leopard frogs), worms, snails, crustaceans, spiders, and other kinds of small animals.
Northern leopard frogs breed in spring, soon after ice and snow have disappeared, usually in March or April, but this varies with altitude and latitude. Males arrive at ponds first and females follow generally 5-7 days later. Egg masses are typically attached to emergent vegetation, including sedges or rushes, but can be unattached. They are generally deposited in water less than 65 cm (26 in) deep and tend to be clumped in areas well exposed to sunlight.
The majority of the mortality among leopard frogs occurs in the tadpole stage. Waterfowl, fish, bullfrogs and aquatic insects are thought to be responsible for much of this mortality. Adults are eaten by snakes during the summer and fall months. Because leopard frogs move from breeding to summer to overwintering habitats, vehicles on roads are a significant mortality source. Roads built between breeding ponds and larger summer, fall, overwintering water bodies can result in large numbers of vehicle-killed leopard frogs.
Bullfrogs, which are native to eastern North America, have the potential to displace native frogs, including northern leopard frogs. Adult bullfrogs are large and will consume almost any moving object which will fit in their mouths. Newly metamorphosed bullfrogs are significantly larger than leopard frogs, and have been documented to eat them.
Sightings of leopard frogs in Washington since 1970 have been from 3 counties; Grant, Whitman, and Pend Oreille. Eighteen Washington locales (from both museum records and historic sightings) were identified in 1992. Surveys were completed in 16 of the 18 areas identified where leopard frogs once occurred. Additional areas were searched by other biologists.
Field surveys conducted since 1992 confirmed the species in only two areas in the state, both of which are in the Crab Creek drainage, Grant County. One historic but unsurveyed area, on the campus of Washington State University, may still be populated by frogs most likely liberated from laboratory experiments. Four separate leopard frog sites at one area in the Crab Creek drainage, and two separate occupied sites at the other area in the Crab Creek drainage have been located. The number of leopard frogs at each of these localities is not known. The number of occupied sites within areas appears to change over time, with surveys indicating some sites disappearing and some newly located.
There are a variety of factors that have potential to adversely affect remaining leopard frog populations in Washington. It is not known for certain what factors alone may trigger extirpation of leopard frogs from a site. Agricultural chemicals have been implicated in the decline of amphibians in other areas. Rotenone used to control unwanted fish can kill leopard frog tadpoles. The increasing spread of bullfrogs, which are known to prey upon leopard frogs and other amphibians, is a major concern. Introduced fish are known to eat amphibians, and are thought to cause significant declines in leopard frog populations.
A number of habitat-related changes have caused declines in other regions and at other sites, and these are possible factors in Washington. Land use changes, irrigation projects, and development have contributed to changes in the hydrology of many areas, potentially affecting amphibians through rapid changes in water levels during critical embryonic and larval periods. Disease may also have contributed to the decline witnessed in Washington. Research, monitoring, and evaluation of the factors potentially causing the decline of leopard frogs are essential to their conservation.
Future population declines are likely to occur in Washington without management effort. A clear understanding of factors causing the decline of the species is needed, as well as an action plan to protect the remaining populations in Washington. Additional field work will be necessary to determine if the leopard frog has been completely eliminated in the areas of historic occurrence where it was not found during recent surveys, or if it survives in places in significantly reduced numbers.
Due to the significant reduction in range and abundance of leopard frogs in Washington, and the continued threats to the remaining occupied sites, it is recommended that the leopard frog be classified as an endangered species in Washington.
Draft documents are provided for informational purposes only. Drafts may contain factual inaccuracies and may not reflect current WDFW policy.