Native tree frogs get a jump on spring

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