Section Menu

Glimpses of Wildlife in Motion Along Mexico’s Highway 2

A man in an orange utility vest stands in front of a small underpass near a busy highway as a truck comes toward him on the highway. Another man in an orange utility vest stands above the underpass on the highway.

This is post 7 of 8 in "Making Mexico's Highway 2 Safer for All."

This blog post series details our work to make Mexico's Highway 2—a dangerous hotspot for wildlife-vehicle collisions—safer for wildlife and people. With a grant from the U.S. Fish and Wildlife Service's Wildlife Without Borders program, we've identified priority areas for potential wildlife crossings and are working with Mexico's transportation authorities to mitigate wildlife-vehicile collisions. All posts in this series…

Leer en español

A group of javelinas (Pecari tajacu) timidly approaches the highway; the rumble of big semi-trucks frightens these wild pigs, as does the sharp smell of gasoline and diesel fumes. They need to cross the road: the urge to find water, food, or shelter just across the pavement is too strong. But venturing onto the unnatural surface could be fatal for them, and they know it.

After some consideration, they wisely decide to cross under the highway, using one of the many drainages designed for sporadic water flows in this arid region with seasonal rains. As they do so, one of our camera-traps snaps a picture of them, providing evidence that wildlife will use these drainage structures to make it safely across what would have otherwise been an almost impermeable obstacle to their movement.

Placing camera-traps on drainages requires some creativity. Here, the staff of EcoGrande try out a camera on the roof of a narrow rock drainage.

Every year, around 2,000 vertebrates die trying to cross Mexico’s Federal Highway 2 in the Sky Islands region of Sonora, impacting the populations of more than 36 species as they move about in their daily business, disperse to new grounds, or, more recently, seek cooler regions in an effort to adapt to climate change.

At Wildlands Network, we’re concerned that the widening of Highway 2 in the last few years, along with increasing border and mining infrastructure, will create a gap separating the more tropical sky island mountain complexes of Mexico from the temperate ones in the United States, forming a nearly-impassible geographic barrier bound to disturb the recovery of species already threatened by habitat loss and other man-made impacts.

Beautiful rock bridges (left) dating from the original construction of Highway 2, sometime after 1940, have been gradually replaced by more austere concrete structures (right) that do not blend as well with the  landscape. While the appearance of the drainage structures might influence an animal’s decision to walk underneath it, there are probably more important factors, such as size and surroundings. Photos: EcoGrande

This is why, for the last three years, we’ve been collecting all kinds of data on Highway 2, from the expansion plans and environmental impact statements to roadkill figures, drainage types and locations, wildlife corridor models, and more recently camera-trap images. We’re using these data to advocate for wildlife crossings, either retrofitted drainages in tandem with fencing and escape ramps, or new structures specifically designed and built for the purpose of letting animals cross the highway safely.

Comrades in Connectivity

Our partners in the region have been instrumental to this effort: Sky Island Alliance’s Mirna Manteca has spent two years collecting roadkill data, all of it available publicly on the iNaturalist platform. Eugenio Larios and Ricardo Félix from EcoGrande, a small Sonoran nonprofit organization, have been our boots on the ground for recording the location of every single one of more than 700 drainages and bridges under Highway 2. Finally, the owners of the private protected areas Rancho El Aribabi and Cuenca Los Ojos have welcomed us and provided crucial insights on the landscape and species they protect.

Preliminary results indicate javelina and coati frequently use drainages as wildlife crossings, suggesting robust connectivity between habitat patches for these two prey species. Photo: Wildlands Network/ EcoGrande/Sky Island Alliance

Now Sky Island Alliance and EcoGrande are setting up our camera-traps throughout two critical wildlife corridors we’ve identified in the region, especially looking at drainages wildlife may use. The pictures these cameras take provide the first tangible proof that wildlife in the area will use the existing structures to safely cross the highway, strengthening our call for fencing to reduce crossings over the pavement, which often result in life-threatening wildlife-vehicle collisions.

Our efforts gained some visibility last September when a female black bear (Ursus americanus) was killed in one of these two corridors, the Sierra Azul-El Pinito corridor, resulting in media coverage of the issue and an exhortation, issued by the State Congress of Sonora, that requests the federal transportation authorities build wildlife crossings in the area.

Path of the Jaguar

It is important to note that the Sierra Azul-El Pinito corridor is not only used by black bears, such as the one killed recently; it is also an important pathway for ocelots (Leopardus pardalis) and is the most likely path used by the majority of jaguars (Panthera onca) who have reached Arizona in the past two decades, a fact that highlights its binational importance.

People of the United States want to see jaguars recover their original territory in Arizona and New Mexico, and that won’t happen if they can’t cross Highway 2. This is why our project has gotten vital support from the U.S. Fish and Wildlife Service through its Wildlife Without Borders Program, a visionary, bridge-building program that sets an example of international collaboration.

The project is also looking at the Sierra Peloncillo corridor, on the eastern side of the Sky Islands, where a promising series of records have been captured by Mirna Manteca: two separate sets of tracks and a photograph confirming cougars are using existing drainages to cross Highway 2. And if cougars can cross under the highway, so can the occasional jaguar.

While blurry, this photo from September 2018 provides evidence of a cougar who crossed Highway 2 using a rock drainage in the Peloncillo mountains, precisely where models suggest jaguar habitat retains good connectivity. Photo: WN/EG/SIA.

There is very little research on jaguars’ use of drainages, but a recent pioneering article by scientists from southeastern Mexico indicates that they will use wildlife underpasses described as structures of “3 meters span and 4.5 meters rise with natural soil” (9’10” by 14’9”). Several of the drainages under Highway 2 are at least this size and most have natural soil, including those used by cougars.

Our roadkill monitoring effort shows that without fencing around these drainages, cougars and other large animals do get hit by cars, as they don’t always choose to cross under the road and, while no one has yet documented a jaguar killed on Highway 2 in Sonora, several recent cases reported on highways of Northwest Mexico—the latest one in June 2018—serve as stark reminders that this could happen at any time, increasing our sense of urgency.

A Challenging Landscape

In addition to wild animals, several people walk past our camera traps. Some of them wear safety vests, most likely to be seen by passing drivers as they search for aluminum cans to sell for recycling. Photo: WN/EG/SIA

Making a highway safe for both black bears and jaguars is one of the unique challenges of working in this part of the borderlands. Another challenge is the large numbers of people on the landscape using the drainages themselves. Humans move near and across the highway, herding cattle, picking bellotas—the nuts from Emory oaks (Quercus emoryi), and migrating north towards the U.S.

Truck drivers are also using them to relieve themselves, out of sight of other motorists. A few of our camera traps have been vandalized or robbed, as expected, but overall the field staff continue to obtain valuable data on what species are using what kinds of structures.

Other people who pass by our camera traps, in camouflage gear, would probably rather not be seen. Photo: WN/EG/SIA

So far, javelinas and coatis (Nasua narica) seem to be the most frequent users of drainages, which might explain why we have only two records of javelinas killed on Highway 2 and very few of coatis. That these two important prey species are adapting to sustain connected populations is good news, but we still need to figure out what other important prey species, especially white-tailed (Odocoileus virginianus) and mule deer (O. hemionus), are doing to cross the highway.

Deer seem to avoid walking into places where visibility is limited, where the chances of ambush increase; therefore, larger bridges are probably more important for them, and we may still need to build a few wildlife overpasses to make sure their populations don’t become isolated.

Deer often walk past drainages that would easily accommodate them, likely deterred by their similarity with caves or dens that could hide a predator. Gif: WN/EG/SIA

Snap Into Action

The incoming pictures of the javelinas, coatis, and a cougar using the drainages—and even those of deer avoiding them—are an invaluable addition to our effort advocating with transportation authorities for the construction of fences and escape ramps on our two focus corridors, projects well within the agency’s capacity and mandate.

Citizens like yourself can also contribute by recording all roadkill you come across on Mexico’s highways in this iNaturalist project. Help us provide the science that can make a real change in the lives of jaguars and other wild animals of the Sky Islands!

Tell us what you think! Note: All comments are moderated before appearing here.