Winners and Losers
While grassland species continue to lose ground in the Southwest, other animals are taking advantage of the region's changing landscape
Don Buckley remembers when javelinas stopped traffic in his neighborhood. "Twenty years ago they were a novelty," says Buckley, a state wildlife manager in Prescott, a small city in central Arizona. "People would get on the phone and tell their friends to come out and watch them."
Since then the human and javelina populations in the Prescott area have exploded and their relationship has frayed. "Now people don't like them at all," Buckley says. "The novelty has worn off. They're tearing up gardens and lawns and eating flowers. We're having more incidents of javelinas biting and killing dogs. It is getting to be a public safety concern."
Javelinas, piglike animals that are also known as collared peccaries, are by no means the only wild mammals that are thriving in the new Southwest. A number of tropical and brush-loving species have expanded their ranges here as the region's landscape has changed within the last century. Meanwhile, other creatures--particularly those that depend upon grasslands for survival--have suffered severe declines.
The explanations behind these shifts involve factors as diverse as climate change, wildfire cycles, livestock grazing and the spread of housing subdivisions. But researchers are finding that it is difficult to tease apart this Gordian knot of causes and effects. Indeed, even the extent of some species' range expansions remains in dispute.
Javelinas reveal how quickly a range expansion can occur. "Peccaries are important game animals anywhere they live, and there's a lack of their remains in archaeological sites in Arizona," says Tad Theimer, a Northern Arizona University biologist who uses genetic analysis to study the peccaries. "That's pretty suggestive that they got here only a few hundred years ago."
In the nineteenth century, American explorers, who generally had sharp eyes for wild protein, reported finding only a handful of javelinas in southeastern Arizona. Yet today the animals are widespread and abundant in the southern and central parts of the state, as well as in much of Texas and southern New Mexico. They have even spread to the pine-clad rims of the Grand Canyon. That is a huge and diverse range, given that the creatures are found as far south as northern Argentina. Two other peccary species also live in South and Central America.
This boom was aided by the Arizona Game and Fish Department, which transplanted javelinas to some new areas of the state up until the late 1970s in an effort to supply more game animals. But most authorities say the creatures have moved north primarily on their own, and in the process, they have caused trouble for many Arizonans.
"Javelinas and coyotes are the two animals that cause the most urban wildlife problems for us," says Pat O'Brien of the state game and fish department. "People move here from elsewhere and have never heard of javelinas. They plant beautiful flower gardens around their houses, and when they get up in the morning those gardens look like they've been hit by a mortar shell."
Javelinas provoke complaints precisely because they can eat almost anything and don't mind having humans nearby. About the height of mid-sized dogs, adult javelinas are covered with bristly hair that seems better adapted to heat than to cold. They roam in bands averaging eight to ten individuals that forage together, largely by smell, as their eyesight is poor. The succulent prickly pear cactus, which provides some moisture during droughts, is a favorite food. So are roots and tubers, including, O'Brien says, tulip bulbs. Though the creatures do not live in areas that are densely populated with people, and seldom move more than a mile to feed, they thrive in many of the state's new developments, where scattered houses stand amid large yards and semiwild areas.
Like pigs, to which they are distantly related, javelinas have formidable canine teeth that can intimidate or slash both real and perceived predators, including coyotes and dogs. "If you're walking a dog on a leash, to a javelina that's a predator," says O'Brien. "It may charge."
Javelina bands are led by females and when a group becomes impractically large, typically a female with her offspring will leave to form a new band. Lone males wander, too. "They have probably followed drainages northward," says Theimer, who has identified three genetically distinct lineages of the animals in Arizona. "The lineage that colonized the southeast corner of the state was the one that has colonized the northwest as well. Animals in the southwest are barred from moving north by large desert basins."
Even montane winters haven't stopped javelinas. "They appear to be better adapted to coping with cold weather than people thought," says Tim Pender, a wildlife manager near the Grand Canyon. "Ten years ago I went to a javelina conference and was told they'd never survive the winters around here. But they do. I've seen them out in snow. They use caves and rock cracks to stay warm. And they form ‘pig piles.' In southeast Arizona I saw 18 piled up in a seething mass, squirming around for warmth."
This northward movement may be only the latest episode in a long story. Peccaries apparently evolved in North America, spread into South America and then died out in the north during the most recent Ice Age. "Basically what they're doing now is following the path of that retreat," says Theimer. "It's a natural recolonization as the environment continues to change since the Pleistocene."
Less controversial mammals have also been on the move. Mexican voles and yellow-nosed cotton rats are believed to have colonized new mountain ranges in Arizona within the last century. And these days opossums are more commonly seen than in previous times in the area between Tucson and the Mexican border. For a while biologists believed these animals were the descendants of eastern opossums transplanted to Arizona. Then a closer look revealed them to be Mexican opossums, which have longer, darker tails than their eastern cousins.
That's not a big surprise, as Mexican opossums are known to exist just south of the border. But experts cannot agree whether this subspecies is a new arrival. "I've always held that this is not a recent immigrant; it just isn't well represented in the historic record," says Randy Babb, a biologist for the state.
Yar Petryszyn, a University of Arizona mammalogist, disagrees. "They have become much more prevalent in far southern Arizona in the last two decades," he says. "The reason for this and other expansions is the two wet decades we've had since 1978." Despite the recent drought in the region, he observes, conditions remain good in many areas for the opossums.
Another animal that appears to be doing well in the Southwest region is less urban: Coatis generally avoid people and their environs. Like peccaries, they are animals of the American tropics and subtropics; coatis are found as far north as central Arizona, New Mexico and south Texas. Some people who have spotted them in the Arizona's southeastern mountains have mistakenly reported seeing anteaters, or even monkeys.
Coatis indeed do have long, flexible tails that they often carry upright, and they move around in small bands. But they're related to raccoons, not primates. They use their sensitive snouts to detect grubs and roots hidden in soil and leaf litter, then use long claws to excavate these foods. They also eat insects, fruits and carrion. Like raccoons, they also get into trouble sometimes for raiding garbage containers, fruit trees and vegetable gardens.
Female coatis stay alone only when giving birth and tending their young in early summer. Otherwise, they roam with their young in groups of 5 to 20 animals, which provide them with some defense against mountain lions, golden eagles and other predators.
Adult males, which are called coatimundis, tend to be loners that are capable of traveling long distances. One male that was moved to a far end of Arizona's Huachuca Mountains after raiding suburban gardens returned the next day, having traveled 12 miles. Those wandering ways may explain why the creatures occasionally turn up in central Arizona and New Mexico. But scientists do not know if those coatis are really expanding the species' range.
Christine Hass, a biologist who runs a coati study in the Huachucas, suggests that fires and overgrazing at the turn of the last century reduced cover and leaf litter, both of which coatis need to survive. Since then, the animals have been rebounding in fits and starts, reclaiming their range, perhaps, rather than expanding it.
Hass believes that coati populations are cyclic. Based on conditions in their habitat, "I think their numbers are going up and down on their own," she says. Hass also notes that coatis were considered pests only a few decades ago because they were erroneously thought to prey on ground-nesting birds, and hunters were given free rein to kill as many as possible. Now coati hunting is strictly regulated and the U.S. population of the animals continues to fluctuate.
Recently, biologists David Brown of Arizona State University and Russell Davis of the University of Arizona set out to examine patterns of known range expansions and contractions among the state's mammals and birds. They found that, in the last century, the expansions exceeded the contractions. And they pinpointed an interesting pattern among those animals that gained and those that lost ground.
"Two kinds of animals have been moving north: tropical species and animals that are adapted to brushy, scrubby habitats," says Brown. "Grassland species are losers; brush species are winners. Boreal species are the losers; tropical species are the winners. This is something that's been going on for 9,000 years, but people have probably facilitated it. Grassland species are losers largely because of human-induced changes."
Indeed, many southwestern grassland species are in trouble. Pronghorn, prairie dogs, burrowing owls and aplomado falcons are all much less common now than earlier in the last century; masked bobwhites survive in the region only because of intensive captive breeding and reintroduction efforts. And some smaller species of birds that nest in open grasslands, such as Botteri's and grasshopper sparrows, are now considerably less widespread in the Southwest.
In many areas, these species' habitats have been altered permanently by livestock grazing and fire suppression. Ecologists believe that millions of acres in the Southwest have been converted from grasslands to shrublands that support snakeweed and other small, woody plants. Such plants provide cover and food for scrub wildlife while depriving grassland animals of the open spaces they need. Artificial water holes built in the region for cattle have also enabled species not truly adapted to aridity, such as javelinas, to weather droughts.
"Javelinas came north after the grasslands got beaten up pretty bad by cattle," says Lyle Sowls, a wildlife biologist emeritus at the University of Arizona and author of a book on peccaries. "They're animals of dense brush and so when we ruined the grasslands, that's when they came in."
Climate change, too, has played a role in the loss of grasslands. In Arizona and New Mexico, average minimum temperatures have been rising since 1960. Two decades of heavier-than-normal winter rains in the Southwest have probably benefited woody species such as juniper and mesquite. And some scientists believe that the current increase in atmospheric carbon dioxide--a by-product of our heavy use of fossil fuels--may be aiding shrubs at the expense of grasses, which utilize a somewhat different method of photosynthesis.
"The encroachment of woody plants in what used to be pure grasslands is one of the most striking changes in the region," says botanist Raymond Turner, an adjunct professor at the University of Arizona who has analyzed historic habitat changes in the region. "But I think it's too soon to tell what impact the changes in CO2 levels or temperatures are having."
While scientists search for more answers, plant and wildlife distributions will continue to shift in the Southwest. "They can change a great deal in a hundred years," observes Russell Davis. "There will always be winners and losers."
A frequent contributor to this magazine, Arizona journalist Peter Friederici is coauthor of the National Audubon Society Field Guide to the Southwestern States (Knopf, 1999).
NWF Takes Action
Restoring Grassland Species in Arizona
Working with an affiliate, the Arizona Wildlife Federation, NWF is involved in a number of activities to protect grassland species and habitat in the Grand Canyon State.
In addition to assisting state authorities in censusing endangered black-footed ferrets at an Arizona release site, the two groups are seeking to restore healthy populations of pronghorn to the Coconino National Forest. These efforts are part of an ongoing NWF campaign called America's Wild Grasslands: Rediscovering and Restoring Forgotten Landscapes.
"As a nation, we can no longer afford to ignore the importance of our grassland ecosystems," says Catherine Johnson, director of NWF's Rocky Mountain Field Office in Colorado.