The basic pattern of the Northern red-legged frog migration is straight forward -- the males go to the wetland first to establish a territory, the females arrive a bit later, generate an egg mass, then return to the forest, with the males continuing to woo more partners before returning themselves -- but how the migration unfolds over the course of the winter is anything but simple. A huge gap in our understanding is we know little about the forest lives of these frogs. Not knowing much about their day to day existence, we don’t know if they slowly ease into migration, going short distances each day, or hop pell mell toward the pond. We don’t know from how far away they come (though we suspect it can be a trip of several miles), or when they begin.
Weather is currently our main complexity in predicting when the frogs move, especially since the migration takes place after dark, with the temperature often dropping below 45 degrees, the “stay or go” temperature threshold of the frogs. Winter evenings in the Northwest are often wet, a condition the frogs require to venture out from the security of wet woods, but, especially with climate change, long dry stretches, sometimes several weeks, are now usual. Sometimes all the conditions seem favorable, and still the frogs stay pat up the hill under a fern, or down in the cold water of the pond.
This leaves we frog people with the enviable task of being ready every night during the migration, with most nights frog quiet. New volunteers sometimes feel like failures, as they’ve been ready for weeks to catch frogs and the pavement is endlessly still. It can take a while to understand that the frogs pick us to catch them, though they would never admit to it. Then there are the nights the frogs break their own rules, like February 11, with temps over 50 degrees but no rain (though wet pavement): 7 females and 1 male were assisted to the pond, and 51 females and 148 males were assisted to the forest, leaving Jane Hartline, the night’s frog captain, to ask, “Did high humidity make conditions as favorable as if it were raining? The moon’s stage? (waxing crescent) Barometric pressure? Simply the interval since there was a big pulse downhill? Was the light rain early in the evening enough to get them all going, and then they didn’t stop?”
More questions, “Seven gravid females went down. Are they just late to the party or did they travel further? Or is this just genetic diversity at it’s best … allowing a range of behaviors so that all the eggs aren’t in one basket.” From February 4 to the 29th there were twelve days when frogs moved: just 1 frog on the 4th, 222 on the 26th, the average haul for those twelve days just over 60 a night, with overall totals looking like they’d be similar to the two previous years; numbers to the wetland and then back to the forest nearly the same. February 26 blew the numbers, and our assumptions, out of the water -- 191 males headed up from the wetland; we’d assisted 686 going down and 890 going up, with a couple hundred more males than females. How did all these “extra” males get to the wetland? Where did they come from?
Last summer was unusually long, hot and dry, with the wetland almost completely dry by the end of July, a tough situation for last year’s tadpoles, and the juvenile frogs still living there from the year before. (Drought is difficult for frogs and salamanders since they must maintain skin moisture, while their cover and sources of water dry up.) To add to the pressure on the young frogs there were the usual two or three blue herons, but instead of the three or four great egrets that had been migrating from the south in previous years, last summer there were twenty-five, chowing down every day. Plus we’d gotten into the habit of counting small frogs as males -- not examining each for nuptial pads on their thumbs that clearly distinguishes them from females. Could we be counting juvenile females as male? Or was there a sudden imbalance in the sexes’ numbers? An early December pulse of males we missed? Late night migrations while we slept? The frogs seemed to be flanking us early on, as if to avoid us. Could they also be avoiding us by simply out waiting us at night? (This could be a good thing.)
Another development in February was an emphasis on catching lots more chorus frogs than we used to, bringing them down from Harborton to sing their hearts out, or squeeze an egg mass onto a blade of grass amid their enveloping cacophony. (It’s amazing to stand in the singing’s midst, with all the layering and pulse.) So small and so numerous we’d been ignoring them in past years; it felt good to that we were taking them in, dealing with their escape artist climbing, and then watching them boinging toward the pond, more lives saved. (Pacific treefrogs remain numerous, their life habits apparently less in conflict with the cluelessness of their upright neighbors than their larger brethren, the red-leggeds.) Smaller than a fifty cent piece, they offer no resistance to being caught (though they squirm in hand). Does their size make flight or fight useless strategies? Their perpetuation as a species relying on numbers and being easy to overlook because they’re so small?
March arrived the same wet lion as the previous months of this rainy winter, with 100 frogs -- nearly all males -- returning to the forest on three nights by mid-month: it looked like we were done for the winter, frog catchers frayed around the edges and the frogs as patient and nonplused as ever. (“Just put me down and go away, pal.”) Of course, another 100 males going up makes the numbers and sexes returning to the forest even more unbalanced. And brought us close to the 1000 frog mark, so at our frog volunteer dinner on March 13, it was decided the thousandth frog should be named “M.” We’d photograph our frog of the hour dressed like a gentleman, sitting at the wheel of an Austin Martin, juggling a martini and a Beretta in one hand, the other firmly anchored under the arm of a gravid female.
By the way, the dinner was a great time, after we got used to seeing each other not in a monsoon suit, and in the light (quite a shock for some of the more sensitive folk, I screamed once myself). We could face one another and not blind anyone with our headlamp, and enjoy each other’s company without worrying a frog was slipping by us to get squashed on the highway. I’m one of those “wouldn’t want to belong to a club that would have me” people, but I must admit, frog catchers are a hell of an entertaining bunch, even without the crowns, green velvet suits and frog scepters.