Frog population hops the croaking line

By Chris Carrel, Thinking Locally

By Chris Carrel, Thinking Locally

Federal Way recently gave me a gift: Frogs.

A mess of Pacific tree frogs to be exact. Was this part of some odd citizen recognition program? Live in Federal Way for 40 years and get free frogs?

No, the frogs are an inadvertent and quite positive result of city stormwater regulations and a recent 28-house subdivision that was built a stone’s throw from my house.

While I like frogs and I like to hear the sound of their calls in the air, they are also an important part of a healthy Puget Sound environment. Native amphibians are a key indicator species of environmental quality (When you’re a coal miner, it’s always a good thing when the canaries are thriving). They feed on insects and invertebrates and are themselves a favored food of other native species, including the garter snake.

The question is, if the city did it once, can they do it again?

We have not had many frogs in the View Cliff neighborhood since at least the late 1980s. Now, we’re lousy with frogs.

As I write this I can hear a couple of tree frogs croaking in my yard and another in the neighbor’s yard. After several close calls this summer, I have had to adopt a very careful lawn-mowing style because of the number of tree frogs in my lawns. This spring when I unfolded my patio table for the warm weather, I was surprised to find a young adult tree frog comfortably chilling inside one of the table leaves.

Stemming from the federal Clean Water Act, the city has to require developments to manage stormwater and prevent pollution to wetlands and streams, and ultimately, Puget Sound. Typically, this is done through stormwater ponds.

Native Northwest amphibians are terrifically picky about breeding habitat — they need certain water depths and suitable plant stems to attach egg masses to. Something about the stormwater ponds at the Ventana Subdivision, however, created the right habitat for amphibian breeding.

After a couple of years in operation, the pond became a regular frog hot spot during breeding season, which lasts from March to May. Tree frogs (also known with good reason as chorus frogs) have a particular, loud two-note call they use to advertise their availability. From my house, roughly 1,000 feet from the pond, the symphony of frogs fills the nighttime air.

After a couple of these loud breeding seasons had gone by, I noticed the proliferation of tree frogs in the surrounding neighborhood.

Tree frogs, like many amphibians, only use wetlands and ponds for breeding. The rest of the year, they move off to surrounding uplands and forests to feed on insects and other invertebrates.

Our neighborhood has plenty of forest habitat. The breeding habitat was the missing ingredient.

I called King County Senior Ecologist Klaus Richter, one of the nation’s preeminent experts on Pacific Northwest amphibians, to find out if the accidental tree frog enhancement could be repeated at other stormwater ponds. The question has also been on Richter’s mind. His graduate students have taken a good look at stormwater ponds and found that 82 percent of them provide breeding habitat for amphibians, without any special frog-oriented design. It appears that most stormwater ponds built in the county can provide that breeding habitat. With a little more attention to design, Richter thinks we could likely increase that capability.

But Richter cautions that our questions that still need to be answered.

“It’s quite possible that these ponds are ecological sinks,” he said, meaning they have a net negative effect.

Since stormwater ponds, by design, receive stormwater runoff, they are sinks for whatever pollutants are running off our roofs, lawns and streets. Copper, herbicides, you name it, it’s going to end up in the pond. It’s quite possible that these ponds could produce diseased frogs who weaken the overall population of frogs when they migrate to their upland habitat.

Not being natural wetlands, the stormwater ponds also attract other species that may not be as positive as tree frogs. One species of snail known to frequent stormwater ponds carries a fluke with it that causes deformities in frogs and amphibians.

Non-native bullfrogs were present in 54 percent of the ponds in Richter’s study. These massive amphibians dine on native frogs, fish, baby birds, whatever they can fit in their mouths. If ponds attract bullfrogs, they could simply be serving up native frogs as a smorgasbord for the nonnative toad.

If there are design features that can produce healthy and sustainable native frog habitat, we can use stormwater ponds to enhance a keystone species in our Puget Sound ecosystem. While Richter’s team is studying stormwater pond breeding habitat, I’ll be keeping an eye on View Cliff’s frog population.

Chris Carrel is a lifelong Federal Way resident and executive director of the Friends of the Hylebos, a nonprofit conservation organization working to preserve and restore Hylebos Creek and the West Hylebos Wetlands. Chris can be contacted at or (253) 874-2005.