Endangered Species Handbook

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Grasslands, Shrublands, Deserts

Drylands of the World: NORTH AMERICA: Page 4

     Pronghorn Antelope, once numbering in the millions in grasslands from southern Canada to northern Mexico, have disappeared from much of their former range.  They have rebounded from near extinction in the Great Plains, but are rare or endangered in the desert grasslands of the Southwest and northwestern Mexico.  Two subspecies are listed as endangered by the U.S. Endangered Species Act: the Peninsular Pronghorn (Antilocapra antilocapra peninsularis) of Baja California, Mexico, and the Sonoran Pronghorn (Antilocapra antilocapra sonoriensis) of the Sonoran Desert of southern Arizona, southeastern California and adjoining Mexico.  These two races have become endangered by a loss of grassland to overgrazing and agriculture and by overhunting.  Sonoran Pronghorn number only between 125 and 250 animals in Arizona, and an equal number are estimated to survive in neighboring Mexico (Turbak 1995).  Remnant populations of this subspecies reside in the Cabeza Prieta National Wildlife Refuge, the Organ Pipe National Monument, and on an Air Force gunnery range.  Smaller than the prairie races of Pronghorn, they can survive in extreme conditions of heat, aridity and sparse vegetation.  It is thought that they are able to live without ever drinking water, according to Pronghorn: Portrait of the American Antelope (Turbak 1995). Their habitat has been severely damaged, and most of the original grassland range of the Pronghorn in the Southwest has been lost to agriculture or has become totally barren after centuries of heavy livestock grazing. 
     Sonoran Pronghorn inhabiting the Luke Air Force Base in Arizona number only about 100 animals, and some have been killed by low-level flight training, air-to-ground live fire and other military activities (Stauble 1997).   Since the Endangered Species Act prohibits federal agencies from harming listed animals, these activities were illegal.  Defenders of Wildlife sued the Fish and Wildlife Service for allowing these lethal activities, and new monitoring procedures resulted in the cancellation of three scheduled bombings in 1997 because Pronghorn were in the vicinity (Stauble 1997).
     The Peninsular Pronghorn is even more endangered, numbering only about 100 to 250 animals in the Vizcaino Desert of the central Baja California peninsula of Mexico (Turbak 1995).  At one time, they were far more numerous and common in this arid region of northwestern Mexico, but they have been crowded out by development and livestock and decimated by overhunting.
     The Mexican or Chihuahuan Pronghorn (Antilocapra americana mexicana) was once native to southeast Arizona, Mexico, and portions of Texas and New Mexico.  In Texas a small population remains near the town of Marathon in Brewster County, but the Arizona Pronghorn disappeared altogether by about 1920 as a result of uncontrolled hunting, agricultural development and livestock grazing (Turbak 1995).  In the 1980s, 400 Chihuahuan Pronghorn were moved from Texas to five sites in Arizona, mainly in the center of the state, and these animals are doing well, having increased to 500 (Turbak 1995).  Their long-term future is not rosy, however, because of the rampant urban and suburban growth taking place in central Arizona (Turbak 1995).  These skittish and extremely high strung animals do not do well in captivity, and no captive herds of either subspecies are being bred in zoos.
     Three of the five native prairie dog species are imperiled. The Utah Prairie Dog (Cynomys parvidens) has been driven to near extinction by rodent control programs and the loss of habitat to livestock and agriculture.  Listed on the U.S. Endangered Species Act, this species has a restricted range in southwest Utah.  A population estimated at 95,000 animals in 1920 fell to only 3,300 in 1972 (Nowak 1991).  Through protection accorded by the Endangered Species Act, Utah Prairie Dogs began to rebound, and by 1984, the species was downgraded from endangered to threatened on the Endangered Species Act.  Counts of Utah Prairie Dogs in the early 1990s ranged from 6,400 in the fall to 24,000 after they had pups in the spring (Nowak 1991).  The Fish and Wildlife Service began transplanting prairie dogs from private to public lands (Turbak 1993).  Initially, many of the released prairie dogs failed to survive, and not until they began releasing males in the spring, who industriously spent the summer excavating burrows to accommodate other prairie dogs released in the fall, did transplants succeed (Turbak 1993).
     In southern Coahuila and northern San Luis Potos, Mexico, the Mexican Prairie Dog (Cynomys mexicanus) has become endangered from poisoning and shooting campaigns by ranchers and farmers (Nowak 1991).  They have lost a great deal of their habitat to agriculture and huge cattle ranches.  The species is listed as Endangered by the U.S. Endangered Species Act as well as by the 1996 IUCN Red List Animals.
     The Black-tailed Prairie Dog (Cynomys ludovicianus) numbered in the billions at the time of Lewis and Clark in the early 19th century. Its range covered the millions of acres of shortgrass prairie.  This species has been decimated by conversion of the land to agriculture and poison campaigns, causing declines of 98 to 99 percent (Wuerthner 1996).   The Biodiversity Legal Foundation in Colorado filed a petition in October 1994 to list this species as a Category 2 species under the Endangered Species Act, a category just below threatened.  Although the Fish and Wildlife Service's own biologists supported this listing, the petition was denied after political pressure from ranchers and South Dakota's Senator Thomas Daschle (Wuerthner 1996).
     Conservation biologists have expressed concern that the remaining prairie dog towns are so small and fragmented that this may cause the prairie town social system to slowly disintegrate (Stevens 1995b).  For a healthy prairie dog ecosystem, reserves of at least several million acres are needed for these animals to recover their natural role in the prairies (Wuerthner 1996).  Some biologists who have studied this situation think that such reserves might be established by purchasing privately owned inholdings in public lands and consolidating portions of BLM land and national grasslands. 
     The image of the prairie dog as a pest to be exterminated is still dominant in the American West among ranchers, and through their influence, almost all public land except National Parks and some National Wildlife Refuges is managed for livestock, with control programs to eliminate prairie dogs.  Poisoning even takes place in a few National Parks that border ranches (Wuerthner 1996).  The fragmentation of their populations may be encouraging outbreaks of disease in the prairie dog colonies.  Sylvatic plague, a disease that was introduced to North America from Asia in the early 1900s, has swept through many prairie dog towns, wiping out entire colonies in a matter of days (Matchett 1997).  The disease is carried by fleas, and prairie dogs have no immunity to the disease (Wuerthner 1996).
     As prairie dog towns disappeared, so, too, did a species that is entirely dependent on them.  The Black-footed Ferret (Mustela nigripes) exists in no other habitat.  With such a complete dependence on these rodents and their burrows, the species was extremely vulnerable to declines.  Even prior to the poison campaigns, these black-masked members of the weasel family, Mustelidae, had been considered rare, and it is amazing that they survive at all.  Ferrets resemble their close relatives, the weasels, in being long-bodied and slim with short legs, well designed to slip into prairie dog burrows.  Rodent control campaigns killed ferrets directly when they fed on the bodies of poisoned prairie dogs (see Persecution and Hunting chapter).  
     A population of Black-footed Ferrets discovered in a South Dakota Indian Reservation in the 1960s died out after poison control programs were implemented. Thought extinct, none was seen until 1979, when two skulls that appeared to be from recently killed ferrets were found in Wyoming.  No living animals were found, however. Then in 1981, a rancher found a dead Black-footed Ferret killed by his dog, and gave it to a Wyoming taxidermist to stuff and mount.  Although the rancher did not recognize the species, the taxidermist realized that the animal was an endangered Black-footed Ferret.  Fish and Wildlife Service biologists came to the property, located more Black-footed Ferrets and began field research.  A young male Black-footed Ferret was live-trapped and fitted with a tiny radio transmitter so that researchers could track his movements.  After that, more ferrets were seen in the same part of Wyoming.  Dr. Tim Clark and his associates counted 58 animals, of which 36 were born in 1982 in this population.   
     This newly discovered population almost died out as well, however, when canine distemper, apparently spread by a pet dog in 1985, killed the majority of the 127 Black-footed Ferrets known to exist (Godbey and Biggins 1994).  Only 19 animals survived of this population, and they were taken into captivity.  In 1992, sylvatic plague struck the White-tailed Prairie Dog town inhabited by the ferrets, killing most of the town.
     Prior to these events, an extraordinary film, “The Mysterious Black-footed Ferret,” was made by the National Audubon Society in the Wyoming prairie dog town, revealing an enchanting creature (see Video Section, Mammals).  They were filmed darting rapidly about in the early morning and at night, often engaging in high-speed chases of one another, zooming in and out of prairie dog burrows and leaping in graceful figure eights.  Arching their bodies in an "S" shape, they danced in circles around one another.  They often seemed to be playing tag.  When an unfamiliar sound that might be a hawk or owl was heard, their black-masked faces appeared suddenly at burrow entrances, and they emitted excited yipping sounds of warning.  They were able to back into burrows at high speed, shuffling backwards so quickly that they were gone in the blink of an eye.
     Fortunately for the species, the captive-breeding program succeeded.  Breeding cages were built in Wyoming, and the project was supervised by the Fish and Wildlife Service. Most of the captive Black-footed Ferrets are housed in units with a den on a lower level connected by plastic pipe to an upper level.  They apparently find the pipes satisfactory substitutes for burrows, zipping rapidly between levels, with several ferrets to each unit.  Gradually, other captive-breeding centers were established, with many zoos taking ferrets.  The captive population rose to 118 animals by September 1989 (DeBlieu 1993) and to 250 breeding adults by 1994 (Godbey and Biggins 1994).  Between 1995 and 1997, 400 kits were produced (Line 1997b).  Genetically, however, the population is in danger of being inbred, because the entire population is descended from only 19 animals.
     No further signs of Black-footed Ferrets have been found in other parts of the West, and had other populations existed, they would probably by now have been poisoned by the prairie dog campaigns that continue.  The Animal Damage Control division (part of the U.S. Department of Agriculture) uses federal funds to poison prairie dogs on millions of acres of federal lands.   After the species was listed by the U.S. Endangered Species Act of 1973, federal employees were required to look for signs of the ferrets, such as tracks in the dirt, prior to poisoning prairie dog towns.  These signs are not always present, however, and it is very likely that many ferrets have been killed by the United States government even after their supposed protection on the Act.
     The present goal of the Endangered Species recovery program for Black-footed Ferrets is to establish new populations in various parts of the West by reintroducing captive-bred ferrets into existing prairie dog colonies.  This goal has been difficult to attain, however, because the majority of prairie dog towns remaining in the West, most of which are on federal land, are still being poisoned.   Tim Clark commented on this situation: "Prairie dogs figure prominently in the ecology of this continent. Does it make sense to try to eliminate prairie dogs and then turn around and declare ferrets endangered and spend of a lot of money attempting to restore them?  We'd never think of burning a museum, yet when it comes to our biological heritage, we don't hesitate to bulldoze it, burn it, or plow it under...To avoid that, we should be protecting prairie dog habitat" (Long 1998).
     Black-footed Ferrets require a large territory and, therefore, a sizeable prairie dog town. In 1991, after much searching, a release site was found north of Laramie, Wyoming, and 49 ferrets were set free; by the following spring, two of the females had produced litters (DeBlieu 1993).  High mortality marked the first releases because these animals had not been conditioned to cope with natural predators.  In 1992, another 90 animals were released, after a period of training in which they were kept in an outdoor pen with prairie dogs; this greatly improved the survival of released animals.  Experiments in which ferrets are born and raised in dirt-filled pens with prairie dog burrows and live prairie dogs have produced the most successful adaptations to the wild of all (Matchett 1997).  Disease still presents a danger:  Of 228 ferrets released in Wyoming's Shirley Basin, only about six animals survived after plague broke out (Line 1997b).   
     The recovery programs have been conducted with the cooperation of state, federal, local and private concerns, and include education campaigns.  Prior to the release of ferrets, local ranchers and others were consulted, and fears that prohibitions of the Endangered Species Act might cause problems if any ferrets were accidentally killed were allayed by the ferrets' designation as "nonessential experimental populations,"  which allows accidental killing without penalties.
     In 1993 and 1994, more Black-footed Ferrets were released in the 1.1 million-acre Charles M. Russell National Wildlife Refuge in Montana in Black-tailed Prairie Dog towns; six of the 12 ferrets were killed by predators, but five of the 1994 releases survived, according to the Fish and Wildlife Service.  Additional releases in 1995 and 1996 totaled 119 ferrets (Matchett 1997).  Only about 30 ferrets were known to survive from these releases.  Since sylvatic plague has been detected among the prairie dogs on the Charles M. Russell Refuge, Fish and Wildlife Service biologists have attempted to control its spread by spraying flea power dust into burrows (Matchett 1997).  Over 65,000 individual prairie dog burrows were dusted, a major undertaking which may prevent an outbreak that will decimate these animals, and extirpate the introduced Black-footed Ferrets (Matchett 1997). Only 10 percent of young survive their first winter after leaving their mothers, and habitat that is free of prairie dog control programs is extremely limited.
     For the future, however, the number of potential release sites in prairie dog towns that are not being poisoned or bulldozed is limited, and funds for ferret breeding and release may dry up completely (Line 1997b).  Federal biologists working on the ferret recovery program have expressed dismay at the lack of public interest in the return of these delightful animals to the wild and believe this will translate into a termination of the program (Line 1997b).  The Fish and Wildlife Service hopes that one of the release sites, probably in South Dakota, may have self-sustaining populations in the future, allowing capture of wild-born young for release elsewhere, rather than supplying captive-bred ferrets at great expense. 
     Both prairie dogs and Black-footed Ferrets could be major tourist attractions, adding to public knowledge about them and support for their conservation.  Prairie dog towns provide constant interest as the little dogs chatter and hug and kiss one another in greeting. Other wildlife, from rare Burrowing Owls to hawks, snakes, tortoises, butterflies and some 170 species, find refuge there.  Tourists would likely find the night spotlighting research of biologists studying the ferrets to be fascinating and often extremely lively. 
     America's largest bird, the California Condor (Gymnogyps californianus), once soared over the grasslands of the West, feeding on carrion.  Centuries of persecution by hunters and egg collectors nearly caused the bird's extinction.  In the 1980s, the last few birds were removed from the wild, where they were dying from accidental poisoning from lead shot in deer carcasses and strychnine from rodent-control programs.  A captive-breeding program has been extremely successful, allowing for the release into the wild in southern California and near Arizona's Grand Canyon of young condors from the population of some 169 birds.  With a 9.5-foot wingspan, these magnificent birds may again soar over wilderness areas of the West, but there have been problems with released birds approaching people’s homes and even entering them, colliding with power lines and ingesting lead shot. Release of adults, especially some of the original condors, to guide the young, which under natural conditions remain with their parents for several years, may be the only answer to a successful reintroduction.
     Fifty-five grassland animals and plants are now listed as endangered or threatened species in the United States (West 1997).  Grassland birds have declined more drastically than birds from any other habitat, according to studies by the Fish and Wildlife Service (Pruitt 1997).  The wild and beautiful prairies and western shrubland have lost many species of plants, insects and vertebrates.  Even where the land has not been plowed, but heavy grazing has occurred, species diversity has declined, and many exotic species of grasses have become established (Peck 1990).  In fact, of all North America's grassland birds, only 10 percent have stable or growing populations, according to the North American Breeding Bird Survey (Line 1997). About 260 species of birds are known to breed in the Great Plains, of which 32 are endemic; settlement and agriculture had very adverse effects on most of these species (Knopf 1988).  At least 13 species of native grassland birds exhibited downward trends in their populations between 1966 and 1995 (Line 1997).  Many of these are among the most familiar and, until recent times, most abundant grassland birds.  Meadowlarks, five species of sparrows, prairie chickens and several birds of prey are among these.

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