their wings in low temperatures, but these bees 

 have powerful muscles that generate their own 

 heat, enabling them to get going early in the morn- 

 ing. Most of the other invertebrates we spotted — a 

 few grasshoppers, beetles, and the like — were flight- 

 less. Some biologists suggest that flightlessness is an 

 adaptation to an environment where wind blasts, 

 unhindered by topography, would blow most flying 

 insects away, but other explanations are possible. 

 For example, flight may be energetically too costly. 



As for the frogs, our hunt began in a series of 

 rocky ponds nearby. Within minutes, Tracie Sei- 

 mon had several specimens of Telmatobius tad- 

 poles — fat, squishy things the size of a quarter and 

 darkly colored, like the bees. The tadpoles have 



Polylepis trees on Mount Sajama grow at elevations as high 

 as 17,400 feet, a world record for trees. In most places 

 Polylepis trees are being exterminated by woodcutting and 

 grazing, as roads penetrate farther upland. 



plenty to eat here: the water is alive with aquatic in- 

 vertebrates. Sowell probed one mucky bottom with 

 a sieve and came up with some pea-size clams. A 

 mollusk expert, Robert P. Guralnick, also of the 

 University of Colorado at Boulder, would later 

 judge them to be among the worlds highest known 

 clams. Descended from an ancient lineage, they had 

 arrived here by unknown means. 



Squirmier things appeared in the sieve, and Sowell 

 shouted: "Look — the world's highest worm! Hey! 

 The world's highest leech!" This "world's highest" 

 business soon became a stock joke with us — but 

 it was true. "We're finding them here because we 

 are looking here," said Halloy. "In most places, no 

 one has looked yet." 



As we stand on our 17,500-foot ridge looking 

 down on the pond we have discovered, Sow- 

 ell and I are not doing as well as those tadpoles. By 

 day, we have been alternately warding off cold in 

 layers of fleece and down, and slathering on sun- 

 block to keep from being broiled. At night, I have 

 awakened countless times in the blackness, gasp- 

 ing; on the autopilot of sleep the body frequently 

 forgets to breathe enough at high elevation. Dur- 

 ing our nasty two-hour scramble through rising 

 ridges of loose boulders, every step has been 

 torture. When we reach the pond, it looks lifeless 

 except for a few spiky plants on the fringes. In 

 search of frogs, we turn over rocks for an hour — a 

 simple task at lower levels, but excruciating here. 



Then I hear Sowell whoop. Cupped in one hand 

 he holds a Pleurodema marmorata the size of a quar- 

 ter — as of this moment, the world's highest known 

 adult frog. Suddenly, we feel invigorated. "I guar- 

 antee you, Trade's going to be up here tomorrow, 

 trying to beat this," he says. 



The next night, Tracie and Anton Seimon stum- 

 ble into camp well after dark. Trade's fingers are 

 bleeding from overturning stones at a high pass 

 above where we had been — 17,700 feet. As 

 recently as the 1990s perhaps as much as fifty feet of 

 ice stood there. Here in this brand-new environ- 

 ment, the Seimons have come upon a sight that 

 stuns them. In the shallows along the edges of at 

 least eight pools, water is frothing with hundreds of 

 black tadpoles — "Like when you draw a big fishing 

 net in," says Anton. 



From mountaintop to mountaintop, life-forms 

 that have adapted to the high altitudes find it 

 hard to mingle across the intervening valleys, and so 

 evolution has taken them on different courses. We 

 move on to Bolivia's highest peak, Mount Sajama, a 

 dormant volcano whose 21,463-foot snowcap rears 

 out of a vast, dry highland plain. The mountain is 

 worshiped by the indigenous Aymara people as a 

 god. Biologists, too, see it as magical, for it is 

 ringed with trees rooted at heights no tree should 

 reach, sprinkled with bizarre-looking plants, and 

 roamed by predators so elusive few humans have 

 ever seen them. 



The trees, which range through much of the 

 Andes, are Polylepis, called quenua by the locals. Few 

 other tree species exist much past 9,800 feet; on 

 Sajama the quenuas go to 17,400 feet, a world 

 record. On our hike up the mountain's arid lower 

 flanks, we pass under their wind-twisted limbs [see 

 photograph on this page]. The biggest ones we see are 

 only about fifteen feet tall, but their growth rings 

 show some are hundreds of years old. 



48 



NATURAL history September 2006 



