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Thursday, March 20, 2008 - Page updated at 12:43 AM

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Natural Wanders

Native tree frogs get a jump on spring

Special to The Seattle Times

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ALEX TRUE KORIATH

A Pacific tree frog sits in the grass on Vashon Island.

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KATHRYN TRUE

A Pacific tree frog can be identified by a dark gray throat sac, which is partially inflated. The males use the sac to make a variety of vocalizations, including the common springtime "advertisement call."

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KATHRYN TRUE

On Vashon Island, Alex True Koriath, 8, allows a Pacific tree frog to perch atop her head. If you pick up a frog, make sure your hands are free of lotion and soap because amphibians dry out quickly. It's best to moisten your hands before you handle amphibians.

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KATHRYN TRUE

A Pacific tree frog sits in the leaves on Vashon Island.

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KATHRYN TRUE

King County senior ecologist Klaus Richter examines sheaths of soft rush in Luther Burbank Park.

If you go

Listen to the chorus

When

The Pacific tree frog chorus peaks in March, but continues through spring and early summer.

Where we went

Luther Burbank Park is run by the City of Mercer Island parks department. It is located at 2040 84th Ave. S.E., Mercer Island. More information: 206-296-4232 or www.ci.mercer-island.wa.us.

The wetlands are located at the north end of the park. Follow the trails to a short boardwalk. Wallace Pond at the south end of the parking lot is also frequented by tree frogs. The best frog chorusing is on a warm evening after a rain, but individuals can be heard calling throughout the day at this time of year.

Other locations

Other promising frog chorus locations:

West Duwamish Greenbelt in West Seattle (www.seattle.gov/parks/park_detail.asp?ID=4401)

West Hylebos Wetlands Park in Federal Way (www.hylebos.org) Wetlands along Bear Creek in Redmond (www.ci.redmond.wa.us) Marymoor Park in Redmond (206-205-3661 or www.metrokc.gov/parks/marymoor)

Soos Creek Wetlands in Kent (www.friendsofsooscreekpark.wetpaint.com)

Cavanaugh Pond Natural Area just outside Renton (www.dnr.metrokc.gov/wlr/lands/natural/cavanaugh-pond.htm)

The state of the frog

With a “jumpoff” celebration ][ on Leap Day 2008, the Association of Zoos and Aquariums announced this to be the “Year of the Frog.” The organization hopes to bring attention to major conservation efforts addressing a worldwide “amphibian extinction crisis” due to rapidly spreading disease, habitat destruction and climate change. One goal is to involve the public in amphibian conservation. To become a “friend of the frogs” and learn how you can help, see www.yearofthefrog.org.

“Pacific tree frog populations appear healthy,” said local expert Klaus Richter. “Although one could argue that with the continued decline of habitat and its quality from increasing human population and developmental pressures their distribution and numbers are most likely going down.”

Field notes

Pacific tree frog (Pseudacris regilla)

Pacific tree frogs come in a wide range of hues, but have four genetically fixed background colors: green, brown, gray and red. Individuals can show one or more of these colors and can vary from pale to quite dark (depending on background brightness), but the basic colors remain the same. Look for the telltale black eye stripe that extends from the tip of the snout to the shoulder. Their long toes are topped with round toe pads making them expert climbers even on vertical, smooth surfaces.

MERCER ISLAND -- At Luther Burbank Park on the island's northeastern shoulder, spring was doing her best to bid winter a hasty adieu, the flora and fauna busily readying for a farewell soiree. Red flowering currant was begging to unfurl, an Anna's hummer was doing acrobatic "this is my turf" dives, and kids were racing their training wheels to the monkey bars.

As if on cue, a tree frog began ka-reeking just as Klaus Richter arrived. One of King County's senior ecologists, with the Department of Water Resources and Parks, he is also one of the foremost authorities on Northwest amphibians -- and an expert in the fine art of frog procurement. He was there to give me a tour of wetlands he designed specifically for amphibians, and to catch a Pacific tree frog.

In a pond near you, thousands of small suitors are tuning up their voices for the annual swamp love-in. Though they grow to just 2 inches, their voluble voices make up a well-known spring chorus oft-used in Hollywood movies as nighttime sound backdrop. Our most widespread native amphibians, Pacific tree frogs live in every county in the state and were named the Washington state amphibian last year.

Spring brings change

According to Richter, tree frogs spend most of the year solo, snapping up arthropods -- spiders and bugs -- with their sticky tongues in woodlands and gardens. Contrary to their name, they stay near the ground hidden in shrubs and grasses, sometimes staking out flower heads as their own "pollinator buffets."

In early to mid-February, male tree frogs begin migrating to nearby wetlands to establish territories and serenade females out of hiding. The males follow the cues of a bout leader, the lead singer of the loud, two-part advertisement calls used for wooing -- generally described as a "rib-it" or "krek-ek."

"The bout leader is a dominant male sought after by females," said Richter. "He has the best quality pitch that probably relates to strong health and reproductive fertility." Males make sounds by inflating a single throat sac that swells to three times their head size.

Females might listen for days before coming to the ponds to choose a mate. As soon as a female draws near her favorite crooner, the male jumps on her back and wraps her in a hug called amplexus (Latin for "embrace"). They may stay conjoined for several hours as she swims through the reeds, but fertilization happens later. After "the hug" the female attaches a quarter-sized gelatinous mass of 10-70 eggs to stems or sticks in shallow water. As the eggs are released, the male fertilizes them. The female leaves the pond within the week, while her mate may stay up to a month, seeking to extend his genetic reach.

Blackbirds sound off

Richter and I followed a path to the edge of the park's north wetlands, where red-winged blackbirds scolded us from the cattails and cedar waxwings squabbled over last year's overlooked berries.

In the early 1980s, developers and stormwater managers wanted to use wetlands to reduce stream erosion and store surface runoff. The proposal alarmed ecologists, including Richter, because of the potential impact on wildlife and their habitat -- surface runoff can be full of pollutants.

"Wetlands are the kidneys of the landscape," said Richter. "They cleanse water and provide wildlife habitat. We studied 19 area wetlands to better understand their functions and discovered that each wetland is unique. We cannot protect just a few wetlands and expect to maintain our species. Our main recommendation was to protect wetlands from abnormal water-level fluctuations from developmental runoff."

Using data from healthy wetlands, Richter sculpted the disturbed wetland at Luther Burbank specifically to attract amphibians and provide optimum breeding habitat, every aspect worried over and executed to be a frog or salamander's swamp of dreams: Breeding sites were constructed in sunny locations (amphibian eggs develop more quickly in warm water). Deeper pools were created near healthy woodlands making it easier for tadpoles to survive and juveniles to reach cover.

Small peninsulas jut like fingers into the water -- greatly expanding the perimeter of the pond edge's productive zone and protective vegetation. An underwater view would reveal ledges sculpted to meet the picky demands of different amphibian species that prefer to lay their eggs at certain depths.

A faux beaver dam at one end of the pond helps stabilize water-level fluctuations from urban runoff and acts as a buffer between it and a lower pond, which is affected by unnatural water level changes when Lake Washington is raised or lowered. Richter's studies found that amphibians do fine with natural hydrological changes after winter rains and summer drought, but don't fare well under imposed changes.

Ethical argument

Our quest continued.

"We should be able to scare them into the pond," Richter said, hopefully parting sedges and grasses. As if to taunt us, frogs called from across the water where we'd been standing minutes earlier.

"Frogs are an integral part of our wetland ecosystem and extremely beneficial," Richter said. "But I wonder why we always have to justify protecting animals and plants; we don't justify Mount Rainier or blue sky. We owe something to this world simply from an ethical standpoint."

Just as we were turning to leave, I caught a flash of green movement from the corner of one eye. "Frog!" I shouted, and in one wet-kneed lunge, Richter was holding it in his hands. He showed me the green-and-brown splotched male's characteristic dark-gray throat sac, and as he gently stroked its chest and belly, the sac began to swell and the frog began ka-reeking in his hand. After a minute, he released it into the water, wishing it well on its journey to paternity. If only everyone could hold a singing frog -- it's like holding the voice of spring in your hand.

Freelance writer Kathryn True, of Vashon Island, is a regular contributor to Northwest Weekend. Contact her through her Web site: www.kathryntrue.com

Copyright © 2008 The Seattle Times Company

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