Answering the Call of the Oregon Spotted Frog

It is the last day of February, a no-jacket-needed, blue sky afternoon. The Twin Sisters Mountains, white with snow, highlight the horizon to the east. Within the wide Samish River valley a grassy wetland, still mostly in winter brown, stretches south. Except for the occasional chatter of a Marsh Wren and the drowsy krrreck-krrreck of a Pacific Chorus Frog, it is quiet.

The familiar intruder, clad in waders, settles in and waits motionless, expectantly. Then there is a faint tapping sound, which surely must be someone making roof repairs in the far distance or perhaps the drumming of a small woodpecker. But soon a second “roofer” or “woodpecker” joins in and now a third, and it is clear that the sound is originating much closer and belongs to our rarest Pacific Northwest endemic amphibian, the Oregon Spotted Frog (Rana pretiosa). One of the frogs is less than 6 feet away—his bright yellow, upturned eyes an identifying feature—as he begins calling again.

In a few areas of lowland western Whatcom and Skagit Counties, this sound is the most welcome proof that spring is arriving and that an imperiled species is persisting.

The Oregon Spotted Frog is listed as federally threatened under the Endangered Species Act and is Washington State endangered. Populations of Oregon Spotted Frog have been monitored at this site for the past 15 years, providing an estimate of changing population size and patterns of habitat use.

The advertisement calls of male frogs function in attracting females, and in some species the calls also communicate the message, “this is mine” and express a willingness to physically defend—if necessary—an area or its associated resources from other males, a behavior defined as territoriality. However, male Oregon Spotted Frogs instead gather to call at communal breeding areas and do not defend territories. An approaching female triggers amplexus—the mating embrace—by one or more males. The winner will be the one who hangs on until the female is ready to release her eggs for fertilization. 

This year, the first Oregon Spotted Frog egg masses would be found about one week after calling began. Each egg or embryo is surrounded by permeable membranes and encased in moist jelly, and collectively the fertilized eggs laid together in a bunch are an egg mass. In most years, Oregon Spotted Frog breeding throughout our region is largely concluded by April, with most of the egg masses in communal piles, which we call “egg mass clusters.” Some males may linger at breeding sites waiting for the last female to arrive, only to be disappointed. As the brief annual breeding period winds down, the story of this year’s progeny is just beginning.

Developing embryos that survive untimely frosts or drying or the unwanted attention of feeding ducks begin to reach hatching stage in late March and all have hatched by mid-April as the water warms. Because breeding sites are almost invariably in shallow water, often no more than 4-6 inches deep, hatchlings must disperse into deeper and more persistent water to survive. It will be at least another 3 months before these tadpoles are ready to metamorphose. And they must also survive a gauntlet of predators throughout their lives, including Giant Water Bugs, Predaceous Diving Beetle larvae, Gartersnakes, Great Blue Herons, Mink, and River Otter, to name a few. 

The Oregon Spotted Frog has disappeared from large portions of its former range, including much of the Puget Trough, the Willamette Valley of Oregon, several watersheds within the Oregon Cascades, all known occurrences in northeastern California, and most parts of the lower Fraser Valley of British Columbia, Canada. None of the surviving populations in British Columbia, Washington, or Oregon are regarded as secure. Threats include continuing habitat changes from wetland draining, diversions, and changes to natural flood regimes; historical removal of beavers; introduced plant species; increasingly drier summer conditions associated with climate change; predation by introduced fish and American Bullfrogs; and other factors. Populations in the Samish River and lower South Fork Nooksack River watersheds—where populations of Oregon Spotted Frogs were not discovered until 2011—are critical to the recovery of the species, but face these same threats. 

To borrow a phrase from Leo Tolstoy, “what then must we do?”

A recent analysis concluded that more than 40 percent of all living species of amphibians—frogs, salamanders, and caecilians (worm-like burrowing terrestrial or aquatic amphibians, found only in the tropics and sub-tropics)—are currently threatened, while increasing numbers are in the most extreme extinction risk categories, a greater percentage of species in jeopardy than in any other vertebrate group (Luedtke et al. 2023). 

Human destruction of amphibian habitats associated with forests and wetlands, disease organisms inadvertently released into areas where native amphibians had little or no immunity, and our introduction of non-native predators and habitat-changing plants are primarily responsible. Worse still, climate change is now the leading factor further deteriorating species’ status. Amphibians are the “canaries in the coal mine” warning us of collapsing ecosystems and the danger that we may be at the beginning of Earth’s sixth mass extinction event. 

What then must we do?

Answering the call of threatened species like Oregon Spotted Frog is one of the great challenges of our time. But there are reasons for realistic hope of averting the worst outcomes if we regard this as a call to action. Evidence-based conservation programs for amphibians will have to utilize a wide variety of tools, including protecting areas of high biodiversity, disease mitigation, captive survival-assurance colonies, controlling introduced species, and habitat management and restoration (International Union for Conservation of Nature SSC Amphibian Specialist Group 2024).

The good news for our Oregon Spotted Frog is that habitat management—which can be achieved with livestock grazing—is effective in maintaining or restoring suitable vegetation characteristics for egg-laying habitat. Additional measures may be needed to hold water for a longer period, and increasingly attention must be given to containing Bullfrog populations. But these measures have also been shown to be effective.

The work is rewarded by another spring when Oregon Spotted Frogs gather to continue their story.

Whatcom Land Trust has spent over 20 years protecting the Samish River Complex and are continuing to steward it into the future. Large-scale restoration is in the works, but in the meantime, Stephen’s volunteer efforts have ensured the frogs are returning!

Literature Cited

International Union for Conservation of Nature SSC Amphibian Specialist Group. 2024. Amphibian Conservation Action Plan: A Status Review and Roadmap for Global Amphibian Conservation. Wren, S., A. Borzee, R. Marcec-Greaves, and A. Angulo (Editors). IUCN SSC Occasional Paper, No. 57. Gland, Switzerland: IUCN. https://doi.org/10.2305/QWVH2717

Luedtke, J.A., J. Chanson, K. Neam, L. Hobin et al. 2023. Ongoing declines for the world’s amphibians in the face of emerging threats. Nature 622:308-314.