Unlikely as it may seem you are looking at a beaver pond backed up behind an actual beaver dam hidden in the reeds. The wary, nocturnal beaver is seldom seen and you will look in vain for the familiar beaver lodge, because Big Bend beavers make do with what the floodplain has to offer. Instead of building wooden houses, these rodents dig burrows in the river bank, foraying from there to feed on willow, cottonwood, seepwillow, and river cane. Around the turn of the century the Rio Grande and its main tributaries abounded with beaver, but fur traders trapped them to the brink of extinction, woodcutters and farmers destroyed their food supply, and cattle feeding in the canebrakes trampled their burrows. It is hard to imagine just what destroying the trees and ground cover can do to fertile land and to a living stream, but a visit to Terlingua Abaja shows you. James B. Gillett, foreman of the famous G-4 Ranch, recalled that in 1885 “the Terlingua was a bold running stream, studded with cottonwood timber and was alive with beaver.” There was one grove of trees where he had seen at least 1,000 head of cattle enjoying the shade. But after the Terlingua mines opened, Mexican farmers established a community at Terlingua Abaja, a few kilometers up the creek from its junction with the Rio Grande. All the cottonwoods up and down the creek fell to construction and hungry mine furnaces and the virgin earth turned bottom up beneath the plow and grubbing hoe. Today this once fertile valley is a wasteland. The Rare Big Bend Mosquitofish The Big Bend mosquitofish (_Gambusia gaigei_) has a miniscule geographic range. Not only is it restricted to the park, as some other species are, but it is also restricted to one pond. The fish was first identified in 1928 in Boquillas Spring. Unfortunately, the spring soon dried up and for some 20 years the fish was thought extinct. In 1954 more were found near Rio Grande Village. This group was later threatened, and a pond was built especially for the fish. But people dumped into the pond other fish that ate this tiny mosquitofish. At one point the world’s only survivors were two males and a female, Rio Grande Villagers that biologists had removed to a laboratory aquarium at the University of Texas at Austin. A cold winter again killed nearly the whole park population, and again the Austin-raised stock replenished it. _Gambusia gaigei_ gives birth to live offspring and has been around as a species since mastodons. They feed largely on mosquito larvae. [Illustration: Actual size]