The Exotic Burro
burros Equus asinus • also called donkey or ass • in the horse family (Equidae) • Females are called jennies, and males are called jacks. • characteristics include long ears and a short mane • stands less than 5 feet at the shoulder • Average weight is 400 pounds. • Colors vary from black to brown to gray. • feed on a wide variety of grasses • Females give birth to one colt per year after an 11 month gestation period. • Range in North America includes the southwestern deserts, mainly in California and Arizona.
What’s a nice burro like you doing in a desert like this? The feral burros now found in the North American deserts are originally descended from the Nubian and Somali African wild ass. These animals have been domesticated in Africa since about 4000 BCE because of their hardiness and load-bearing capacity. All equines had vanished from North America at the end of the Pleistocene, but Spanish explorers reintroduced horses and burros (Spanish for ‘donkey’) to the continent in the 1500s. Burros were again used as pack animals in the western United States during the gold rushes of the 1800s and the subsequent Westward Expansion. Most of the burros currently living in the desert southwest are descendants of burros who escaped from or were released by their owners during this time. Consequently, some wild horse and burro advocates feel that these animals are an important element of the folklore and cultural history of the West.
Desert Adaptations • Burros are perfectly suited for the habitat of the desert southwest because of their African ancestry. • Prospectors and settlers used them for precisely these qualities. • They feed on a wide variety of shrubs and grasses and have an exceptional ability to locate food in the barren desert. • A burro’s only habitat requirement is to be within 10 miles of a water source. • Burros can tolerate a loss of 30% of their body weight in water and may replenish this loss in five minutes of drinking.
1976-- an estimated 3,400 burros live in California. Currently, approximately 7,000 burros live in CA, AZ, and NV. Burros in the Desert Southwest 1997-- approximately 1,650 burros live in the Mojave National Preserve. 1993-- an approximate total of 7,500 burros live on BLM lands.
'Exotic' Burros?? Yes, burros are exotic to the North American deserts. They occur as a species only because humans introduced them to the area. Without this introduction, burros would not have naturally evolved in North America. This is important in environmental policy- making because burros must be considered as unnatural elements of the desert ecosystem. The native species of the desert have been affected, for better or worse, by the introduction of burros, and the current managers must decide how to achieve an ecological balance with or without the burro.
Burros’ Effects on the Desert Environment Because of their suitability to the desert environment in the Southwest, burros have thrived to the point of damaging the natural ecosystem. They have been accused of harming native species and degrading the physical environment. Burros put a severe drain on desert resources, as an adult may eat 6,000 pounds of vegetation per year (17 pounds per day) and drink 2,000 gallons of water per year.
… environmental effects Resourceful foragers and digesters that they are, burros can have a great impact on the sparse vegetation of the desert. When foraging, a near-constant activity, burros crop the grasses and shrubs down to the roots. This not only damages the native vegetation, but also destroys food and habitat for other species.
Bighorn Sheep One of the most often cited desert rivals of the burro is the bighorn sheep. In most cases, these two species are in direct competition over territory, food, and water. Burros are able to compete extremely successfully because of their enhanced ability to digest woody plants and other desert survival capabilities. Burros have also been accused of fouling water holes and being highly aggressive, thereby driving bighorns from their natural range.
Desert Tortoise A desert species of special concern is the desert tortoise. Although it may not seem obvious at first, burros have a severe negative impact on these threatened reptiles. Burros disrupt the tortoise’s habitat and eat some of their most important foods. Specifically, burros eat certain high protein plants that are essential for tortoise reproduction rates. The U.S. Fish and Wildlife Desert Tortoise Recovery Plan lists the removal of burros from tortoise habitat as necessary for the management of tortoise populations.
more and more burros… The burros in the desert southwest would not be considered such a problem if their numbers were lower. However, burros are generally considered to be ‘prolific’ breeders, and annual growth rates range from 11-29%. Their populations simply continue to balloon because of a lack of natural controls, such as disease and predation. The two natural predators of burros in the desert, mountain lions and coyotes, are ineffective controls. So, most colts reach maturity and may live up to 25 or 30 years.
Without natural controls on burro population, humans have had to take the responsibility of managing burros in the wild. • From the 1920s through the 1960s, the standard control was federal and public hunting. • A future possible control is sterilization, and research is being done on immuno-contraception techniques in hopes of reducing population growth rates. Population Controls
Wild and Free-Roaming Horse and Burro Act Federal Law 92-195 passed in 1971 • Requires the protection, management, and control of wild horses and burros on public land. • Recognizes wild horses and burros as symbols of West. • States that wild horses and burros contribute to the diversity of life forms in America and therefore enrich the lives of the American citizen. • Protection– from capture, branding, harassment, and death. • Management– requires that wild horses and burros be considered as and integral part of the natural system of public lands and be managed within the multiple use concept. • Control– allows for the removal of excess animals in order to preserve and maintain a thriving natural ecological balance. • Wild horse and burro concerns put under the control of the Secretary of the Interior.
Capture and Adoption Programs The most widespread form of burro control since the 1971 Act has been capture and adoption. Methods of capture include helicopter herding and water enticement After capture, animals are transported to BLM adoption program facilities or to non-profit animal sanctuaries.
Capture and Adoption: Criticism • Program does not significantly reduce population because of high growth rate. • Many adopted animals may have later been sold for slaughter although this is in direct violation with the program conditions and the Wild Horse and Burro Act. • The burro market is being saturated, and there will be fewer willing adopters in the future. • Those animals which are not adopted are kept in captivity at great expense. For example, $2.6 million in federal funds were spent maintaining 6285 unadopted animals.
Burros in Death Valley and the Mojave National Preserve
Death Valley-- Burros have been specifically targeted as responsible for the decline in bighorn numbers. Some contest the view that burros have driven bighorns from their original range, citing geologic evidence. It may be that burros prefer the Precambrian or Cambrian geology that bighorns never used because the bighorns stay to Paleozoic carbonate formations. Mojave-- Of special concern here is the desert tortoise. In efforts to preserve the tortoise’s critical habitat, NPS’s ultimate goal is the complete removal of all burros from the Preserve.
The National Park Service administers both Death Valley and the Mojave and is not subject to the same Wild Horse and Burro regulations as the Bureau of Land Management. Prior to the California Desert Protection Act, the lands of the current park and preserve were managed by the BLM, which had determined burro populations consistent with its policies. The NPS has agreed to an interim policy of maintaining BLM determined populations until a new management program is devised.
Controlling Burros in the Mojave National Preserve The NPS has been capturing burros and putting them up for adoption as it tries to eliminate them from the Preserve. In 1998, the NPS entered an agreement with The Fund for Animals, whereby the Fund assumes responsibility for the burros and cares for them at the Black Beauty Ranch in Texas.
Burros have gone from trusty pack animals to feral nuisances in their 400 year history in North America. The current challenge for policy-makers is to manage burro populations in order to protect the desert environment, while keeping in mind that it is not the burros’ fault that they are here and survive so successfully. Capture and adoption programs are one option that has worked. Hopefully, this success will continue, and burros will become less of a problem in the desert southwest.