Our Human History of the Frog Migration

It was a dark, stormy, early January evening -- a little on the warm side -- when Shawn Looney picked me up to go to an important meeting.  Shawn was excited; the road below was covered with frogs!  We descended to the hairpin and turned.  Shawn hit the high beams and there they were, the wet pavement exploding with frogs.  They were hopping all over the place, jumping into the headlights from the dark shoulder, crossing our little side road toward the four lane highway down below, raging with rush hour traffic.  Shawn was terrified she’d run over them, and I went from worry about the lives of the frogs to concern for my own as we jerked back and forth between the guardrail on the left and the cliff face on the right, trying to avoid hundreds of hopsters.  I wanted to yell, “Aim the hood ornament at them, it’s the tires that get them,” but shut up and held on.  Down at the stop sign we were suddenly out of the bedlam, quickly on the highway and speeding along like everyone else.  Little did I know that the frogs had silently slipped in and commandeered large slices of my life, although they’d probably insist they didn’t have much use for me at all.

The next morning I walked down to catch the bus.  There were about 60 dead frogs on the road.  The cars so quickly obliterated them it was hard to get an accurate count.  The air had a fish smell I’ve learned to find sorrowful.  If 60 had been killed, with one car passing every five to ten minutes on a sleepy country road, who could say how many were run over on the highway.  Frogs that make it to the pond next to the river under these circumstances -- across two roads, railroad tracks and a four lane highway at rush hour -- should have constellations named after them, or at least new ponds.  I got in touch with Sue Beilke, a biologist at Fish and Wildlife, who came up and looked over the situation.  They were Northern Red-legged frogs and they lived in forest and bred in ponds and lakes, migrating early in January. Healthy ecologies have huge numbers of them, as they are critical to the food chain. Sue and I looked at places where we might be able to build tiny pools, spoke of carrying frogs across the highway in buckets.  Eight months after meeting with Sue we had a meeting of local frog minds from city and state agencies and a college or two.  Jane Hartline took on the volunteer organizing, and a month later I was standing in the dark with Sue, waiting for the first frog.  We would be frog butlers till almost April.

2014, the first year of the great Harborton Northern red-legged frog roundup was a rousing success, at least as far as the humans were concerned.  The frogs weren’t talking.  Well, they were, but they’re hard to understand, though the chatter coming from the buckets sounded an awful lot like complaining.  Many cheerful and kind volunteers stood in the cold rain, waiting for another migrational pulse of these secretive, surprisingly beautiful creatures.  My neighbor Brian brought us a fat female in his lunch pail, and Pat, my next door neighbor, bailed me out when I showed up a few minutes late one night to check on the frogs to find our biggest migration of the year in full hop.  Frogs were everywhere and Pat, coming home from work, parked, and caught four and five at a time while I ran up to the house to get my phone (which I’d forgotten) to call in reinforcements.  The frogs were always taking us by surprise, but a little background is perhaps called for at this point.

The scene of this adventure is the north edge of Portland, Oregon, just before the Willamette River makes a sweeping curve to its confluence with the Columbia.  The river’s narrow floodplain ends abruptly; a steep, forested ridge jutting a thousand feet up.  This is Forest Park, a 5,174 acre, green peninsula protruding from the Coast Range into the city.  This floodplain was once covered with sloughs, ponds and lakes, and the Red-legged frogs came down from the forest in great numbers to breed in the still waters.  In healthy habitat these frogs can comprise upwards of 60% of total animal biomass.  They are on every predator’s menu; very large numbers are the norm. In one pristine lake in Olympic National Park over 13,000 egg masses were counted, each mass with 1,000 eggs. For Forest Park, and surrounding woodlands to be healthy, we need lots of these frogs.

A dirt track made its way from the small village of Portland in the 1850s, winding along the edge of the ever present water, slipping between giant trees, the ten mile trip to Linnton taking most of the day.  Small farms sprouted along the river and the road improved over the decades.  The railroad plowed through in 1889, the tiny mill town of Linnton booming from 1905 to 1915, its population going from 400 to 2000.  Dredging spoils from the river, and the hydraulic jetting of nearby hillsides, were used to fill the lakes and ponds.  St. Helens Road was straightened and graveled, a trolley line dinging through Linnton in 1911.  Automobiles and pavement, tank farms and industry; life sustaining water treated as a problem in our odd world.  The breeding wetlands of the frogs was nearly all filled, industry and means of travel cutting the forest off from the river almost completely.  In the early 60s the country road was widened into a four lane highway, and not only were there precious few puddles for the frogs to go to, now they had to brave ever increasing numbers of cars and trucks. Then we stumbled upon this startling migration.  I’d never even heard of Northern red-legged frogs, much less seen one.

Three small vernal creeks plunge out of the forest, are kidnapped by culverts to go under pavement and tracks, then meander their way to fill one of the only declivities left along the river, which happens to be down below my house. This pond grows to several acres in size by January, when tiny chorus frogs light their blaze of singing each night under winter sky.  We knew the Red-legged frogs migrated after dark, in wet, relatively warm (above 45F) conditions, but lots of questions remained, so we were vigilant, dedication growing as we became more familiar with these charismatic creatures, reinforced by Sue’s fierce loyalty to them.  We began our vigil on January 8, 2014, Sue and I standing in the dark fifty feet on either side of Harborton Creek.  It was raining lightly.  The creek falls was louder than the traffic on the highway, binding us to the water and woods.  

The idea is to welcome the frogs out by being quiet and still.  I followed my breathing a bit, in, out, in, out, the sounds around us strong in the dark.  The falls drummed stone with tonal undercurrents, the traffic roar approached constant, then broke random.  After a while something moved on the glistening pavement.  In my excitement I forgot to turn my headlamp on, stepping quickly the thirty feet to the frog, dropping the net over him, suddenly afraid of catching him, of hurting him, taking the cold alien in my hand for the first time since I was a kid.  I picked him up through the net, then reached under and grasped him around the hips and brought him over the Sue.  She complemented me on picking him out in the dark.  He was thin, sand brown, and stretched out, six inches long, and squirming surprisingly strongly.  I put him in the bucket and we had our first frog. (We quickly abandoned the nets, hands quicker and better.  Usually when caught in the head lamp’s beam the frog will freeze, a great avoidance strategy in dead leaves, where they seem to disappear into thin air, but not on the pavement.  The best technique is fingers curling over the snout, palm over eyes, as they relax for a few moments.  Grabbing them around the body or hips invites them to struggle.)

Four days later, on January 12, wet and 52F, we had our first big night: 65 males and 13 females.  The males go down to the pond first, the much larger females, fat with eggs, come later.  Jane Hartline, our volunteer coordinator, had created a schedule and phone tree.  Our core group; Sue, Jane, Shawn, Anne Squier, Jeff Booth, and I, each headed an evening crew (I got two), monitoring temperatures, conditions, watching for movement, with a couple helpers, and others on call for the nights when frogs moved. February 12 we caught 108 males and 171 females, our biggest night of that winter’s migration (most nights we didn’t catch anything, the conditions not right or the frogs just not feeling like it).  Then it occurred to us we were going to have to get the frogs back to the forest from the pond.  Sure enough frogs began heading back to the forest February 23.  Females headed back sooner than the males, who, it’s safe to assume, were looking for more rendezvous with late arriving females.  March 2 saw a large pulse going back to the forest; 125 females, 5 males, and two days later the largest pulse returning to the forest; 134 females, 29 males.  March 8 we had the largest number of males returning, 46, with 28 females. 

Very occasionally a female would emerge from the forest with a male already on her back.  (The males have very long, “nuptial” thumbs, which they slide under the female’s arms to get a firm grip.  The long thumbs are the surest and easiest way to identify males.  Once thrown together in the buckets it was common for the males to mount females, which seemed to cause irritated frog chirping and bucket thumping struggle.)

For a number of days in the middle of the two migrations -- down to the pond, then back to the forest -- we’d have to cover both the forest edge; Harborton Drive, and the pond; Marina Way.  It could be hard to tell if an individual frog was coming or going; they might not be facing either up or down when we caught them.  As an experiment I’d put these confusing ones in the middle of Harborton, facing neither up or down to see which way they’d go; they’d just sit there, apparently happy to be in the middle.  I’d walk up behind them to prod them a bit.  They’d ignore me, then finally head one way or the other with gusto.  (Usually into the forest.)  That first frog catching winter, 2014, we caught 226 males, 346 females, 8 we’re not sure of their sex, for a total of 580 frogs.  We counted 94 killed.   We also caught Pacific chorus frogs, long toed and northwestern salamanders, a garter snake and one bullfrog, with was euthanized in a freezer (they’re an invasive disaster for other pond creatures).  We continued to monitor Marina Way till the end of March to make sure no more frogs were migrating.

The next winter, 2014-15 our core group began monitoring Harborton Drive, taking temperatures and noting conditions, on November 24, to make sure the frogs didn’t try anything funny.  They didn’t.  After a few weeks of this, with nothing happening, just standing there watching rush hour traffic hurtle by, the amount of time you want to stand there tends to shrink. December 20 was my turn to monitor.  I walked down from my place carrying a five gallon bucket (a five inch hole cut in the center of the lid, the plastic edges dulled with tape), a head lamp, phone, and a thermometer.  It was warm and drizzly, but still three weeks from when we thought they’d migrate.  I sat on the guard rail, then wandered around in a haphazard circle that traced where we caught most frogs on Harborton, and sat back down on the guard rail.  Nothing was happening.  It’d been dark for twenty minutes, and I headed up to have dinner.  Fifty yards above the creek, where we rarely caught any frogs, there, sitting a few inches onto the pavement, was a male frog.  I put the head lamp’s beam on him, he froze, and I stepped to him.  I reached down and the cagey sucker jumped straight between my legs.  I spun around but couldn’t find him in the leaves, he’d vanished.

Damn, now I had to stay!  I went back down and in the next two hours caught about 45 frogs, having a good time, and called Shawn so she could take the frogs in her car down to the pond.  A couple people spelled me after a while and I went home.  36 males and 18 females were caught that night; the frogs keeping us on our toes.  Then there was a long dry spell, nothing happening, until January 17; about 50 degrees, raining hard and all hell broke loose.  The frogs must have gathered like an invading army at the forest edge, hiding under ferns, biding their time.  They started moving as soon as it was dark.  Then the rain really came down, along with the frogs.  The falls roared, growing to at least three times the flow of the photo, completely overwhelming the culvert.  The three foot deep ditch that ran along the road quickly filled, the frogs riding its torrent down the hill to the stop sign at the bottom of the road, where they slipped out of the current before it got to the culvert by the highway and made a break to get by us and across the highway and its traffic.  We were running around cutting them off at the pass and grabbing them at the highway edge.  

It was a joy watching them swim in the current, being frogs and all; gracefully handling the rush of water, emerging from the torrent to sit nonchalantly at its edge.  When we approached them they’d wait till we were three feet away and elegantly dive backwards, disappearing into the rushing water.  It was hilarious.  We were as wet as the frogs, running around laughing, looking for buckets to put more frogs in.  I got the distinct feeling they were on to us; they remembered us from the year before, and now we were another in the long list of indignities they had had to address for their kind to survive.  At the same time it felt like they were learning the drill; they seemed easier to catch, and once in the buckets they seemed more patient than the first year.  They have funny little voices like tiny children squeaking high and wispy and we’d hear them in the bucket complaining bitterly about being treated so shabbily.  One little guy got by us and dashed across two lanes of traffic, then stopped to wait on the narrow meridian.  (Stop for a second and think about how terrifying it would be for this small creature, who lives an extremely quiet life of solitude in the forest, to be confronted by hundreds of roaring steel giants smashing by at incredible speed.  You might say we’re cavalier about life.)  There was a lull in the southward traffic and I went out to grab this smart frog, but in the chaos I couldn’t find him, and, cars coming, had to get off the highway.  We caught 179 males that night, and 263 females.  

By January 27 the frogs were already heading back up to the forest, with 151 females caught that night (no males).  February was dry, so the frogging was nonexistent, but we had to stay on our toes; they’d fooled us so often.  March 11 was a big night with 134 males caught and 51 females.  Between Marina Way and the raised tracks -- main and a siding -- was a puddly ditch.  The siding, next to the road, usually had a long string of lumber cars parked.  Frogs often paused at the first track, and one could reach under the rail car and catch them.  (One of my best grabs was a frog sitting on top of the rail.)  The railroad started calling the sheriff, which made for more excitement for us, and surprised, friendly deputies.  The totals for the winter of 2014-15 were 695 frogs going to the pond and 750 coming back to the forest.  Some of the larger number returning to the forest can be attributed to juvenile frogs hatched the year before making their first trip to the forest, something we hadn’t seen the first year. 

For more detailed information about Northern red-legged frogs, and more complete data sets of our collecting, please see the Science and History page.

Photo credits: Jane Hartline and Rob Lee