SNFPA Draft Supplemental Environmental Impact Statement

June 2003

Chapter 3: Affected Environment

3.2.2.9. Northern Leopard Frog (Rana pipiens)

The information below was extracted and compiled from the following reference: USDA Forest Service. unpublished. Draft Conservation Assessment for the Northern Leopard Frog (Rana pipiens). USDA Forest Service, Pacific Southwest Region, Vallejo, CA. Detailed references can be found in that document. This section updates and supplements the information found in FEIS Volume 3, Chapter 3, Part 4.4, pp. 226.

Habitat Requirements

The northern leopard frog has been called the "meadow frog" for its summertime movements away from 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.

In Minnesota, the typical breeding pond of leopard frogs is described as "temporary pond with a maximum depth of 1.5 -- 2 m (5 -- 6ft.), that does not support a fish population, is not connected with any other body of water, and dries up periodically every few years." Merrell noted that the distance between overwintering and breeding sites was often 1-2 km (0.6-1.2 mi) in Minnesota. Hine et al. use a simple model to identify potential leopard frog breeding habitat. They first located potential overwintering ponds (permanent, deep water), and then surveyed all temporary ponds within 1.6 km (1 mile) of these potential overwintering sites.

These frogs commonly emerge in early spring (March or April) and males immediately begin calling for mates. During this time, frogs are concentrated in or around lentic water bodies where courtship and spawning takes place. After breeding, adult leopard frogs move away from ponds to a variety of habitats nearby. The distribution appears to be related to a variety of factors, including available food, adequate cover, and moisture. They can be anywhere from a few meter from a pond to as much as 1.6 (1 mile) away. They avoid areas with grass over 1 m tall, wooded areas, open areas lacking vegetation, or heavily grazed or mowed areas. Leopard frogs usually move at night, and will make greater summer movements on rainy days.

After metmorphosis, young frogs may emigrate from their breeding ponds to more permanent water source, like a lake or stream. Small frogs often congregate along the shores of these water sources. They appear to segregate from larger frogs by remaining at the water's margin. Emigration occurs in late July in Minnesota and early July in Iowa.

Movements in the fall begin with cooler weather, often in September. Movement generally take place at night, but frogs may move on dark rainy days as well. Overwintering occurred between the months of October and April in Minnesota. Overwintering habitats are larger lakes and streams that do not freeze completely during winter. Leopard frogs do not hibernate during winter, but activity levels are much reduced. Frogs can be found wintering among stones or sunken logs, in leaf litter or vegetation depressions along the bottom.

Mortality

Merrell reports that the majority of 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. Garter snakes (Thamnophis spp.) are thought to be a common predator of leopard frogs. Because leopard frogs migrate from breeding to summer to overwintering habitats, vehicles on roads are a significant mortality source. Roads built between ponds and larger summer, fall, and overwintering water bodies can result in large numbers of vehicle-killed leopard frogs. The lack of oxygen in water inhabited by overwintering leopard frogs has resulted in large winter kills.

Tadpoles may be eaten by numerous vertebrates and invertebrate predators. Among the vertebrates are belted kingfishers (Ceryle alcyon), hooded mergansers (Lophodytes cucullatus), common garter snakes (Thamnophis sirtalis), western garter snakes (T. elegans), and neotonic tiger salamanders (Ambystoma tigrinum). Turtles may also prey upon tadpoles.

Many introduced species, including largemouth bass (Micropterus salmoides), pumkinseed (Lepomis macrochirus), brown bullhead (Ameiurus nebulosus), black crappie (Pomoxis nigramaculatus), carp (Cyprinus carpio), and rainbow trout (Oncorhynchus mykiss) have been introduced to waters within the historic range of the leopard frog and may have played a role in losses of leopard frog populations. Drought is apparently an important source of mortality as well. Corn and Fogleman document local extirpation of leopard frogs when drought dried ponds in the fall and winter months. Hine et al. found 2 of 5 breeding ponds to not produce young because they dried up prior to metamorphosis one year. He also found that in 1976, during the worst drought in a century, only 4 or 23 ponds that had breeding activity produced frogs.

Historical and Current Range and Distribution

According to museum records, northern leopard frogs historically inhabited several isolated locations of California with most of the populations occurring in or near the Sierra Nevada. Populations were clustered in three main areas, south of Goose Lake (in the surrounding vicinity of Alturas; Modoc Co.), Lake Tahoe (El Dorado Co.), and areas in and around Bishop (Inyo Co.).

The most recent records of the species (near Tule Lake, Siskiyou Co., 1990 and Round Valley near Bishop, Inyo Co., 1994) are the only specimens on record in California in over two decades. Their locations fall within two of the three main clusters of records for the state. However there have been no systematic field verifications of historical northern leopard frog locations in California. It is, therefore, impossible to reasonably deduce whether this species is currently viable or even extant.

Status

The Northern Leopard frog is listed as a sensitive species on the Region 5 Regional Forest's Sensitive Species List. In addition, the species is a California Species of Special Concern.

Risk Factors

For a summary of risk factors, reference the SNFPA FEIS, Chapter 3, Part 4.4, page 226.

USDA Forest Service · Pacific Southwest Region