Dave Bradford is becoming a mad scientist, or at least a madder one, as we splosh through this half-frozen High Sierra Meadow. We are up to our gaiters in a viscous mixture of mud and snow, stalking the wild Mountain Yellow-Legged Frog, the highest dwelling amphibian in the U.S. Our search is along the headwaters of the Kaweah River in Sequoia National Park has so far been in vain.
Bradford is upset because it looks like the previous brutal winter has done-in the entire population of Rana muscosa, the subject of his UCLA Ph.D. thesis. We’ve hiked to several unnamed lakes and found them still covered with ice. Bradford is worried about a frog kill, which, like a fish kill, occurs when lakes don’t thaw and bacteria and fungi on the bottom consume all the oxygen.
We concentrate our efforts on a number of nameless football-field-sized lakes. (Larger lakes tend to have trout as well as names—the presence of fish being a strong incentive to man’s naming proclivity—and trout tend to devour any Yellow Leg tadpoles that have the misfortune to be born in their vicinity.) It is on the banks of one of these unnamed lakes that we discover a grisly sight. Hundreds of yellow frog legs, minus their owners, are scattered about on shore. It looks like an amphibian version of the Donner Party.
“Blackbirds,” Bradford mutters. He’s seen such carnage before. As the tadpoles changed into froglets and hopped ashore, the birds pounced on them, eating everything but the nice, plump legs. Obviously not gourmets, these blackbirds.
Dispiritedly, we follow the Kaweah and ascend above timberline to a lush basin. Bradford changes into green sneakers, green shirt, green hat, green shades. The frogs must sense a kindred spirit because he immediately finds a Mountain Yellow Leg. It’s a large female that he banded the previous summer. Bradford is delighted; after some 150 winter and summer days up here, he’s become a bit unscientifically fond of the little buggers.
The captured frog stoically endures the indignities of the tape measure, the scale and the rectal thermometer. Vital statistics: 68 millimeters from snout to rump; weight 27.3 grams; temperature, 22 degrees centigrade (a medium-warm frog). Stoicism, I soon learn, is what the MYL frog is all about.
Bradford goes about collecting tadpoles, leaving me to watch the female Yellow Leg and to guard his instruments from a marauding marmot. The frog moves but once in the next hour to snatch at a fly. She misses.
“Not too entertaining, are they?” teases Bradford, returning just as I’m picking up the frog to make sure it’s still alive.
“It smells funny,” I note.
“The frog secretes a mucous that doesn’t taste good,” he confirms. “Blackbirds and garter snakes like them, but they’ll eat anything.”
After 48 hours of observation, it is clear why no nature film crew has ever gone after the MYL. The lifestyle of this noxious-smelling creature seems deliberately un-dramatic. It hibernates seven to nine months a year in icebound ponds and is active (if you can call it that) for three to five months. After a night spent resting in the bottom of a lake or stream, it rises well after the sun and swims to shore. Here it makes its major decision of the day: where to bask in the sun. Once it finds a sunny spot, it moves only when the sun changes angle or to swallow flies. The MYL frog is known as a sit and wait predator and seems equally adept at both sitting and waiting. Gulping three flies in twelve hours is a good day’s work. If the frog finds an especially nice, sunny spot, it may occupy the same square foot all day. Sometimes a Yellow Leg will join twenty or more of its fellows in a group bask, huddling in a heap, presumably to reduce heat loss.
Except for their communal basks, Yellow Legs are not sociable creatures. They croak only when stepped on, and it is a feeble call, more like a baby wrentit than a bullfrog. Courtship, carried on in the icy water, is a brief and desultory affair, but the sex act itself is prolonged and may go on for several days. The male, somewhat smaller than the female, hops on her back and with his special calloused thumbs, squeezes her behind the armpits. He massages out her eggs and fertilizes them in the water. The jelly-like eggs stick to aquatic vegetation, and the partners swim blithely off in opposite directions.
All in all, the MYL frog wants little more out of life than to stay warm; its ability to survive temperature extremes is what makes it an attractive research subject to Bradford. He implants transmitters in some of the frogs’ bellies so that they give off a signal. The result is a series of beeps on an AM radio. So many beeps equal to so many degrees. The temperature readouts are quite accurate until a garter snake swallows the transmitting frog and becomes a transmitting snake. Snakes have completely different temperatures and can really screw up Bradford’s data if he’s not careful. To retrieve the expensive transmitter, Bradford must track down the snake and induce it to vomit, which comes naturally to the snake (it often vomits to offend predators or to lighten its load for a quick escape) but leaves everyone feeling a bit raw.
The MYL is a survivor. You have to respect this creature, whose chance for long life is as low as its metabolism. No other amphibian and few other life forms can withstand the extreme cold, the high elevation, the ruthless predators. Some of the frogs live to the ripe old age of 25, Bradford believes.
Although he conducts his research in one of the most beautiful alpine meadows on earth, there’s little that is romantic or idyllic about his work. A campus flyer he circulated describing the delights of frog research failed to lure any pretty coeds into the Sierra. Bradford’s nights are long and lonely. The silence is broken only by the radio, which receives but two transmissions: a rock station from Gilroy, and the endless beeping of his transmitting frogs.