The bar­ri­ers along the US–Mex­ico fron­tier carve up habi­tats and age-old mi­gra­tion routes, im­pact­ing on a host of species.

BBC Wildlife Magazine - - Borderlands - Words and pho­tos by Krista Schlyer

At the south­ern end of Ari­zona’s Huachuca moun­tains, the United States meets Mex­ico on a rocky precipice where a sweep­ing vista un­folds. To the east, the in­ter­na­tional boundary reaches to­wards the hori­zon through an ocean of pale win­ter grasses where jackrab­bits hide and great horned owls hunt. To the south, the deep grooves of the up­per San Pe­dro River wa­ter­shed stretch across the bor­der, ex­tend­ing into the foothills of the Huachu­cas as se­cret pas­sage­ways for bob­cats and black bears. To the west, the im­mense San Rafael Val­ley sprawls south­wards as a sea of golden grass where shy pronghorn an­telopes roam. And all around, dark moun­tain ranges tower like is­lands in the lazuli desert sky, their deep­est shad­ows shel­ter­ing the foot­steps of jaguars.

This land­scape ra­di­ates a wild calm, but be­neath the sur­face are two con­flict­ing re­al­i­ties: the bor­der­lands re­gion en­com­passes one of the most bio­di­verse ecosys­tems in North Amer­ica, while rapidly be­com­ing one of the world’s most mil­i­tarised and di­vided places. Over the past decade, just over 1,000km of bor­der wall have been con­structed along this 3,200km-long fron­tier. Most con­struc­tion has been ex­empted from en­vi­ron­men­tal laws that would have pro­tected crit­i­cal habi­tat and mi­gra­tion path­ways for en­dan­gered species. And in Jan­uary, the new US pres­i­dent vowed to ex­pand bor­der wall con­struc­tion and to in­ten­sify mil­i­tari­sa­tion of this land.

Yet from a steep moun­tain­side over­look­ing the bor­der, geopo­lit­i­cal ten­sion drifts away on a fresh west­erly wind. This im­mense land­scape re­mains the kind of spe­cial space where wildlife can thrive, and hu­mans can find that unique brand of respite par­tic­u­lar to vast open spa­ces.


Seek­ing out some of this wild so­lace, I hike a trail from the Mon­tezuma Pass in Coron­ado Na­tional Memorial, a pro­tected area man­aged by the US Na­tional Park Ser­vice, through the moun­tains to the bor­der, where a mon­u­ment was placed in the 1850s when the United States bought this land from Mex­ico un­der the Gads­den Pur­chase.


Such mon­u­ments were erected all along the bor­der, from the Pa­cific Ocean to the Gulf of Mex­ico. But to­day this par­tic­u­lar one car­ries a weighty im­por­tance – it is sit­u­ated on one of the few mi­gra­tion path­ways re­main­ing to a suite of transna­tional grass­land species.

The US–Mex­ico bor­der, a line drawn in the sand by two na­tions, is fun­da­men­tally de­fined by a nat­u­ral boundary at the over­lap of the tem­per­ate and trop­i­cal zones. Here the north and south meet and min­gle, shar­ing an as­sort­ment of trees, cacti, wild­flow­ers and grasses that don’t co­ex­ist any­where else. Nat­u­ral bor­ders like this are un­usual places, prone to bi­o­log­i­cal ex­trav­a­gance.

Prior to the Gads­den Pur­chase, this land was claimed by Mex­ico, and be­fore that Spain. In the mil­len­nia that pre­ceded Spain’s con­quest of North Amer­ica, it was the do­main of na­tive peo­ple; and be­fore that, it be­longed to the jaguar.

Strength, adapt­abil­ity and stealth earned the jaguar its po­si­tion as an apex preda­tor in the Sono­ran Desert. “Jaguars evolved here in North Amer­ica be­fore they moved south into the trop­ics. So in a very fun­da­men­tal sense they be­long here,” says Randy Ser­raglio, a con­ser­va­tion ad­vo­cate for the Cen­ter for Bi­o­log­i­cal Diver­sity. And some­where out within this grass­land sea, or pad­ding through shad­ows in the river cor­ri­dor, the jaguar still roams. Only now the big cat is fight­ing for its ex­is­tence in an arid world at the boundary of two na­tions.

In the early 20th cen­tury, jaguars started to dis­ap­pear,

largely due to hunt­ing and habi­tat loss. In 1963, the last known fe­male jaguar in the United States was killed near the Grand Canyon, and for decades the largest cat in the western hemi­sphere was feared to have been driven to ex­tinc­tion in the US. But then, in the 1990s, a ray of hope ap­peared in the form of a pho­to­graph cap­tured in south-east Ari­zona. Since then, there have been hun­dreds of pho­tos and sight­ings of male jaguars. “We don’t know where the near­est fe­male is,” Ser­raglio ad­mits. “We know there is a breed­ing pop­u­la­tion around 200km south of the bor­der, but we don’t know if there are some closer, even in the United States. Jaguars are so cryptic.”


Re­searchers know that young male jaguars are com­ing to the US to find new ter­ri­tory. They live here for a few years un­til a bi­o­log­i­cal urge kicks in, and then head back to Mex­ico to find the near­est fe­male. “They have to go back,” Ser­raglio says. “They have to find a fe­male.”

Jaguar re­searchers be­lieve that when the north­ern­most fe­male jaguars be­gin to branch out, if mi­gra­tion path­ways are open to them, they will find their way to the United States. And when that fe­male pi­o­neer ar­rives, Seraglio says, it will be a game-changer. In the mean­time, con­ser­va­tion or­gan­i­sa­tions have been work­ing to raise aware­ness and cre­ate a plan for restora­tion. Cen­tral to jaguar con­ser­va­tion are two ba­sic needs: space and path­ways for travel.

“Like most apex preda­tors, jaguars need large areas of wilder­ness,” Ser­raglio ex­plains. “And they travel long dis­tances to find what they need. Con­nec­tiv­ity is crit­i­cally im­por­tant for jaguars.” This puts the fu­ture of this cat at the mercy of the pre­vail­ing US pol­icy of build­ing walls and ex­pand­ing mil­i­tari­sa­tion of its south­ern bor­der. “If jaguars are ever go­ing to re­cover in the United States, the breed­ing pop­u­la­tion in north­ern Mex­ico must be able to ex­pand north,” Ser­raglio says. And jaguars are not alone.

The US be­gan in­ten­si­fy­ing bor­der en­force­ment in 2005 when Congress ap­proved sev­eral mea­sures aimed at fast-track­ing the con­struc­tion of a wall. In ad­di­tion to man­dat­ing 1,120km of wall, the fed­eral mea­sures re­moved en­vi­ron­men­tal and other bedrock pro­tec­tions for land, peo­ple and wildlife. Since that time, about one-third of the bor­der has been walled, largely over land­scapes set aside specif­i­cally for wildlife and wilder­ness.

Dis­missal of en­vi­ron­men­tal law along much of the bor­der has jeop­ar­dised pop­u­la­tions of nu­mer­ous species, in­clud­ing the jaguar, ocelot, col­lared pec­cary, pronghorn an­te­lope and black bear. For many species, the wall poses a di­rect threat by block­ing ac­cess to scarce water and food re­sources. Bar­ri­ers have also iso­lated in­di­vid­u­als from mates on the op­po­site side of the

bor­der, which wor­ries bi­ol­o­gists.


A 2011 study found that black bears in the Sierra Madre moun­tains are ge­net­i­cally linked with bears across the bor­der in south-east Ari­zona; any bar­rier that sep­a­rates bears in Mex­ico from those in the US will threaten this iso­lated south­ern pop­u­la­tion. “Black bears are much less abun­dant in Mex­ico,” says Juan Car­los Bravo, who di­rects the Mex­ico Program for the Wild­lands Net­work, an or­gan­i­sa­tion fo­cused on restor­ing land­scape con­nec­tiv­ity. “They de­pend on open cor­ri­dors into the United States for ge­netic diver­sity.”


The fall­out from this may not be­come ap­par­ent for years, as ge­netic poverty takes its toll on the bears. But for some species, the grow­ing di­vi­sions in this land­scape have al­ready hit hard. Im­me­di­ately af­ter the bor­der wall was built in the Or­gan Pipe Cac­tus Na­tional Mon­u­ment, sci­en­tists filmed Sono­ran Desert toads jump­ing against its steel, time af­ter time, un­til they were taken by preda­tors or died of de­hy­dra­tion. In 2012, a herd of pronghorn in the San Rafael Val­ley be­gan dis­ap­pear­ing. An in­ves­ti­ga­tion found that af­ter the bor­der bar­rier was put up, all of the breed­ing males were iso­lated on its south­ern side.

All of these im­pacts were pre­dictable out­comes of adding large ob­sta­cles to the land­scape, Bravo notes. “It goes against mod­ern con­ser­va­tion prac­tice to build a bar­rier.”

The con­struc­tion of a bor­der wall has

de­stroyed and frag­mented crit­i­cal habi­tat all along the bor­der. In Texas, where the Rio Grande de­lin­eates the fron­tier, more than 95 per cent of the na­tive habi­tat has been lost to hu­man de­vel­op­ment. The re­main­ing five per cent is lo­cated al­most en­tirely on wildlife refuges along the river cor­ri­dor. This scant re­main­ing habi­tat pro­vides a life­line for en­dan­gered wild cats, im­per­illed rep­tiles and in­sects, and glob­ally im­por­tant bird pop­u­la­tions.


More than 500 species of bird de­pend on the Lower Rio Grande Val­ley. Many make their homes along the river, while oth­ers rely on its rel­a­tively lush sur­round­ings to rest and re­fuel af­ter gru­elling flights over the Gulf of Mex­ico or the vast deserts to the west. Ev­ery re­main­ing acre of na­tive habi­tat here may make the dif­fer­ence be­tween death and sur­vival for mi­gra­tory birds such as north­ern car­di­nals, al­tamira ori­oles, green jays, kiskadees and many more.

Bob­cats also use the Rio Grande. But in 2009 re­searchers found that af­ter the bor­der wall frag­mented wildlife refuges in south­ern Texas, bob­cats were killing bob­cats and dy­ing on roads as they fought over shrink­ing ter­ri­tory and roamed the Lower Rio Grande Val­ley search­ing for new homes.

For con­ser­va­tion­ists, the rise of bor­der walls con­sti­tutes a tragedy of epic pro­por­tions for thou­sands of wild species. And this threat to global bio­di­ver­sity goes well be­yond the bor­ders of North Amer­ica, as more na­tions re­in­force their bor­ders world­wide.

Here in the Huachu­cas, look­ing out over the San Pe­dro River and the moun­tains ris­ing above the Mex­i­can grass­lands, the in­ten­tion of newly elected pres­i­dent Don­ald Trump to ex­pand the US–Mex­ico bor­der wall casts an omi­nous pall. For now, how­ever, the bor­der at the foot of the Huachu­cas is de­fined by a 2.5m-high barbed-wire fence. It poses lit­tle ob­sta­cle to the jaguar, which can jump over this bar­rier or sneak un­der if need be.

Re­cent ev­i­dence shows jaguars are do­ing just that. In late 2016, a cam­era-trap cap­tured the im­age of a new jaguar in Ari­zona – one whose sex could not be de­ter­mined. The mere pos­si­bil­ity it may be that lon­gawaited fe­male caused jaguar con­ser­va­tion hopes to soar. But to the east of the Huachu­cas, an 11m-high wall has al­ready been built right up into the foothills, a wall that stretches for dozens of miles across the San Pe­dro Val­ley.

I my­self have wit­nessed nu­mer­ous species trapped by this wall, in­clud­ing col­lared pec­ca­ries, an­i­mals with an im­por­tant eco­log­i­cal role as both a prey species and seed dis­trib­u­tor. The im­pos­ing ed­i­fice also blocks the pas­sage of pronghorn, mule and white-tailed deer, cot­ton­tail rab­bits and in­deed ev­ery other ter­res­trial animal, through one of the most crit­i­cal pas­sages in the re­gion for wildlife.

Cli­mate change can only worsen the sit­u­a­tion, as it be­gins to ex­ac­er­bate droughts and in­ten­sify heat in the desert. “With such huge un­cer­tainty due to cli­mate change, we have to pre­serve the op­tions for these species to adapt,” Ser­raglio says. “One of the best ways to do that is to main­tain con­nec­tiv­ity.”

The bor­der­lands rep­re­sents the only vi­able fu­ture for the jaguar in the US, and for so many other species en­twined in the re­gion’s web of life. Each crea­ture here has adapted to sur­vive in a desert, but their great­est test may yet rise be­fore them. “For thou­sands of years jaguars were revered by in­dige­nous cultures as su­per­hu­man,” Ser­raglio says. “But they can’t climb that wall.”


Clock­wise from top left: the best hope for the con­tin­ued sur­vival of bighorn sheep is open travel cor­ri­dors; the bor­der wall has frag­mented bob­cat habi­tat; kan­ga­roo rat pop­u­la­tions are be­ing split by walls built through the Cal­i­for­nia dunes; elf owls...

Clock­wise from above: the bor­der wall now bi­sects the grass­lands of the Coron­ado Na­tional Memorial and San Pe­dro River cor­ri­dor; a gila mon­ster on a con­ser­va­tion prop­erty in Mex­ico; al­tamira ori­ole in Lower Rio Grande Val­ley; a male jaguar in south­ern...

Above: a desert cot­ton­tail at the bor­der wall dur­ing its con­struc­tion in south­ern Ari­zona. The bar­rier re­stricts the pas­sage of the species and other land mam­mals.

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