Earth & Sky

Thanks to:

Laura Todd
Wildlife Biologist
USFWS

Cheryl Friesen
Wildlife Biologist
Willamette National Forest
USDA Forest Service

References:

Interview with Laura Todd.

Washington State Status Report for the Oregon Spotted Frog, July 1997 by Kelly R. McAllister and William P. Leonard Washington Department of Fish and Wildlife, Wildlife Management Program

Conserving the Oregon Spotted Frog in the Mink Lake Basin Willamette National Forest

Pacific Biodiversity Inst. Oregon Spotted Frog Information

Background Information

The Oregon Spotted Frog is endemic to the Pacific Northwest. It can be found in the shallow areas of springs, lakes, ponds, and slow-moving streams with abundant aquatic vegetation. The Oregon Spotted Frog is very similar in appearance to the Columbia Spotted Frog, both frogs were once thought to be a single species.

As their name implies, the Oregon Spotted Frog has spots, irregularly-shaped black spots that run along the sides, back, and legs. The overall color of the frog is olive green or reddish-brown tan. On larger frogs, presumably older frogs, the abdomen is usually red. This frog has upturned eyes, short hind legs with fully webbed feet.

Oregon Spotted Frogs are almost exclusively aquatic. They are opportunistic feeders, often preying on live insects like beetles, flies, water striders, and ants. They, in turn, are the natural prey of garter snakes and herons. Their eggs are eaten by various aquatic invertebrates. Unfortunately, the frogs are also a major prey of introduced aquatic species like the brook trout and bullfrog, major contributors to their decline.

Breeding occurs in late winter or early spring. The males emit faint calls that sound like the distant tapping of a woodpecker, during both day and night. After mating, the females lay their eggs in shallow still waters, among vegetation. About 18 to 30 days later, the eggs hatch. The brownish-green tadpoles, their intestines still visible, feed on algae and rotting vegetation. About 13 to 16 weeks later, they develop into frogs. These juveniles will reach sexual maturity around 2 to 3 years of age.

The Oregon Spotted Frog has seen a dramatic decline in population over the past 2 decades. Much of it is due to habitat loss, as shallow wetlands are diked and filled to create habitable land for human settlements. Because the frogs have never evolved defenses against aquatic predators, they have fallen easy prey to exotic introductions like brook trout and bullfrogs. A Conservation Agreement, a joint effort between state wildlife agencies, the U.S. Fish and Wildlife Service and the U.S. Forest service, has been created to to save this frog species. These agencies will monitor the frog populations, work on protecting frog sites, conduct habitat surveys, and create more public awareness for this unique creature of the Pacific Northwest.

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Notes from an interview with Laura Todd, U.S. Fish and Wildlife Service.

Oregon Spotted Frog.

Q: What is the current status of the frog?

This animal is currently a candidate species for the Endangered Species listing.

The declining number of frogs has been noticed in surveys over several years, for instance, in 1983 and 1985 in Oregon. The frogs are most abundant in Oregon, with about 26 to 27 populations. In Washington, there are about 3 to 4 populations left and in British Columbia, Canada, only two populations remain. The frogs were once found in California but have since been extirpated.

The declines were first documented in the early 1970s by Dr. Robert Shaw of Oregon State University. The problem likely started as far back as the 1940s. Sites that were once documented to have frogs no longer have them. The species has disappeared in 70% of its original range, mostly gone from the northern part of its range.

Q: What’s causing the decline?

The primary reason for the frog’s decline is habitat loss. The introduction of exotic fish and bullfrogs has contributed as well.

The high mountain lakes were historically fishless. The frogs therefore never evolved a mechanism for avoiding aquatic predators, making them easy prey. They never leave the water, not even to escape.

In the past two decades, there has been a major decline in the frog population. This is mainly due to urbanization and industrialization, as the suburbs spread out, especially in the lowlands. From the 1940s to the 1970s, the land was severely converted using dikes, levees, and ditches by the U.S. Army Corp of Engineers. Although farmland has been around a lot longer in these areas, it was not a major cause of the frog’s decline, since farmland had ponds that could be suitable habitat for the frogs.

Bullfrogs were introduced in the early 1900s to be farmed for froglegs. But as this delicacy became less in vogue, and less profitable, the frogs were released. They have become predators for Oregon Spotted frogs in some places.

Q: Where are most of the frogs found?

Most of the frogs were once found in the Willamette Valley. Today, this area is mostly urban with some agriculture. Four major cities are located here – Eugene, Portland, Salem, and Corvalis.

In Oregon, there are two major Oregon Spotted Frog centers. The biggest one is in the Deschutes Basin, in central Oregon (east side of Cascades). There are 19 to 20 populations of frogs that are well-linked. There hasn?t been as much development in that region, but some habitat has been lost. Work is underway with private large landowners to set up a conservation agreement, in Sun River, south of the town of Bend, on the Little Dechutes river.

The second major frog center is in the Klamath area.

There are some other smaller populations in southern Oregon, about 4 to 6. A few isolated population are also found, 2 in Washington, and 1 in Oregon.

Q: What are the habitat requirements for the frogs, and what’s being done to conserve them?

The frogs need permanent bodies of water, with shallow, warm water for laying eggs. They go to the same place each year to lay their eggs. There are also habitat requirements for overwintering – the frogs need areas of flowing water that keeps ice from forming on the surface. During the winter, local migrations occur where the frogs move to places with running water like springs, or where water enters lakes.

The frogs are mainly opportunistic feeders, and eat various types of aquatic invertebrates. They only feed in the water. This dependence on water makes them very vulnerable to contaminants, and they are easily affected by fertilizer runoff.

Some conservation measures are underway. One exotic predator, the brook trout, is reproducing in the high lakes. Studies are being done to determine how best to get rid of these exotic fish, such as blocking the fish from entering frog areas, removing the fish using gill nets, creating physical barriers to protect egg-laying sites, and allowing fishermen to have an unlimited take on brook trout. It?s believed that drought years are especially hard for the frogs, since water levels drop, leaving aquatic vegetation stranded above the water line. This removes the protective cover for frogs, making them more vulnerable to falling prey to brook trout.

Another step that has been taken, this in the Willamette National Forest, is to relocate trails that are too close to the lakeshore. People and horses have trampled on the aquatic vegetation, degrading the habitat. By moving the trails further from the lakeshore, much of this vegetation is being preserved for the frogs. Monitoring of the frogs is also underway – age, size, genetic studies – to better understand these populations and what?s needed to conserve them. Land use planning is another important factor, steps such as increasing buffer widths along water, reducing pesticides on golf courses, and hand-pulling exotic weeds.

In the high Cascade lakes, bullfrogs are not a major problem. Although they can overwinter as tadpoles, bullfrogs cannot survive winter lake freezes. The bullfrog problem is mainly confined to lowlands. They have been seen and heard in the Sun River area, and some work is being done to capture them.