Green Gulch, Chisos Mountains
by Betty Alex
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The Sky Island concept originated in an Arizona Highways article in the early 1940s when the writer referred to the Chiricahua Mountains in far Southeastern Arizona as mountain islands in a desert sea. Over the next 20 years the term morphed into “Sky Islands,” because the concept of mountains as “island habitat” took hold in the scientific community. Using the science of island habitat in Sky Island Mountain ranges has led to greater understanding and more successful management of those areas.
The Sky Islands of the Southwestern U.S. and Northern Mexico are not isolated enough to have the same level of extreme speciation as oceanic islands like the Galapagos, and they are generally open to human visitation with only a few restrictions on numbers of people, camping locations, etc. making them only somewhat protected from human damage. But isolation still produces instances of speciation and distinct subspecies that inhabit only the “local” Sky Islands, and habitats that are preferred by already rare species.
Because of their isolation and small size, Sky Islands remain quite vulnerable to human and natural extremes. Drought and severe freeze are, overall, more impactful to the Sky Islands of the Southwest than they are to equivalent areas in larger mountain ranges like the Rocky Mountains and Sierra Nevada. Fire, natural or man-caused, can devastate large portions of a Sky Island range. One of the potential issues in fire situations is the damage to wildlife populations. Mammals, birds, even insects can occasionally migrate between the mountain islands, thereby allowing genetic mixing from other populations. However, invertebrate populations (like earthworms, insects, and spiders) rarely survive or escape from any intense fire, and amphibians (frogs and toads), reptiles (turtles, snakes, lizards), and small mammals (mice, rabbits, ringtails, raccoons, squirrels) are highly vulnerable due to their inability to escape a fast-moving fire. Any post-fire rainfall runoff will flood water courses and carry ash and chemicals released from the burned vegetation into areas not directly affected by the fire; this can harm sensitive species (including plants). Fire retardant is an unnatural chemical that has been shown to adversely impact aquatic systems. EXTREMELY limited use of fire retardant occurred during the fire suppression activities in the Chisos.
Invertebrates
One notable invertebrate in the Chisos Mountains is the Chisos Metalmark Butterfly, known only from the Chisos Mountains (there is one unconfirmed report from another Texas site approximately 200 miles away). Endemic to the Chisos, it is listed by the State of Texas as Critically Imperiled. The caterpillars of this small but quite beautiful orange and brown butterfly eat Havard plum leaves, a beautiful little shrub in the Rose Family that is endemic to the Big Bend area and adjacent Mexico–an endemic butterfly relying on an endemic shrub. The adult butterflies emerge twice each year, Spring and late Summer. The general habitat is on the lower slopes of the Chisos Mountains where Havard plum is most common. The area of the recent South Rim 4 Fire in the Chisos might have impacted a small area of the habitat, but most was outside the fire area.
There are other understudied invertebrate species in the Chisos area, like the Big Bend Quonker—an exceptionally loud katydid (Paracyrtophyllus excelsus) that inhabits the southern Big Bend area, and the Chisos Scorpion (Vaejovis Chisos), known only from the Chisos, neither of which has been well studied. Both would be highly susceptible to dying in any larger fire. I personally know that there are stable populations of both species outside the area affected by the fire.
Mammals
The major issue that arises for wildlife during wildland fire is ESCAPE. Most people think of wildlife as the large mammals and birds that are generally able to flee a fire. But, in almost any wildland fire, even large, fastmoving, mammals like deer, bear, mountain lions, bobcats, coyotes, and foxes may become encircled by fire, flee to an inescapable location, or are simply overcome by the speed of the fire’s spread. If those larger mammals have young that are still in the nest or den, there is no escape for the young, and their loss impacts the entire population for at least a year.
The deer in the Chisos Mountains above 3800 feet are the Carmen Mountains Whitetail Deer (Odocoileus virginianus carminis), named for the Sierra del Carmen, Mexico. These deer are exceptionally small and generally considered the smallest continental deer in North America. Only the island-evolved Key Deer of the Florida Keys are smaller.
The Carmen Mountains deer are known to be scattered among the Chisos, Rosillos, Chinati, and Christmas mountains in the Big Bend, and the Sierra del Carmen, Coahuila, Mexico. They are the product of Sky Island ecology, not occupying the areas between mountain ranges and only slightly overlapping their territory with the more common Mule Deer.
The area of the recent South Rim 4 Fire encompasses much of the Carmen Deer habitat. Because the fire intensity ranged from extreme to slight understory burns with some areas within the perimeter untouched by direct fire, decent cover and habitat still exist in the High Chisos. The deer do range considerably outside of the burned area to the edge of the forest and into the high desert shrubland, occasionally being spotted as low as the Panther Junction Headquarters area, and the Dodson Trail. Fawns normally drop in July–September, so direct damage to the young of the year is minimized.
The Bears of the Chisos are the Mexican Black Bear. They were extirpated from the Chisos and northward by the late 1930s. But in 1989 a pregnant female black bear migrated north from the Sierra de Carmen, Mexico, just south of the Rio Grande and took up residence in the Chisos. She and her three cubs from that year reestablished a bear residency in the Chisos and it has become a stable and healthy population over the intervening 30+ years.
The Mexican Black Bear is smaller and skinnier than the common Black Bear that occur to the north in New Mexico and the Rocky Mountains. They are adapted to the hotter drier Chihuahuan desert. Unlike most other North American bear, they do not hibernate—they estivate, taking long ‘naps’ during the winter rather than going into the complete torpor of hibernation. Their dens are quite deep in rocky crevasses that would not be severely affected by most fire occurrences. It is not uncommon for weather events to rouse them from their slumbers, and knowledgeable people have suggested that the fire and fire suppression activity probably awakened any bears in the Chisos that were estivating. The fire occurred around the time the bears would normally be coming out of their winter estivation.
Young would probably be reasonably mobile by that time and escape would be expected. The bears now range widely across the Big Bend area and are quite comfortable living in the shrubland and desert areas. In recent years, bear sightings have regularly occurred outside the park. Several of the smaller mountain ranges and swaths of high hills are known to have seasonal bear residents.
Forage in the High Chisos for bears, especially in the burn area, was affected by the fire, but it is generally expected that the larger than usual pinyon nut crop and the fact that they can easily forage outside the burned areas will allow them decent food availability.
The old joke “Where do Mountain Lions live?” “ANYWHERE they want to” is appropriate for the current situation. There are lions whose primary territory is in the Chisos, but the territories are far larger than just the burn area. When mountain lions were being actively tracked, some that were routinely found in the Chisos were also tracked as far as the north end of Old Ore Road, or down to the Rio Grande. Females are not as wide-ranging as males, but they are not locked into an area as small as the High Chisos. Mountain lions are not locked into a seasonal production of young, so while there could have been cubs too young to flee that were still in a den in the High Chisos, that is not particularly likely. And while dens might be reused, the lions are not locked into a specific den and can adapt easily. Because displaced small animals that escaped the fire will be easier prey while they are attempting to reestablish themselves in a new area, the mountain lions will probably fare quite well through the summer and into the fall.
The Mexican Long-nosed Bat is listed as Endangered by the US Fish and Wildlife Service and was once thought to be found only in Big Bend NP in the US. A few other breeding colonies have been found in SE Arizona and southern New Mexico. The bats migrate from their wintering grounds in Mexico in late May or early June. Their arrival is timed to coincide with the blooming of the Havard Century Plant (Agave havardii), a large agave that only grows in and around the Chisos Mountains. The bats give birth and raise their young while feasting on the nectar of the Century Plant blooms. There is one cave in the Chisos that holds a large maternity colony. Disruption of that colony area during the June-August period could significantly impact the health of the entire colony. Thankfully, the fire occurred earlier than their arrival time and did not impact the area of the cave. Outside the burn area, there are significant numbers of blooming Century Plants for the bats to feed upon, so the breeding season will probably be successful.
Birds
Big Bend National Park is known for having more bird species than any other National Park—over 450! There are several that receive both management efforts by the NPS and visitor attention.
For 40 years the signature bird of the Chisos has been the Peregrine Falcon. Listed as Endangered in 1970, it is an excellent example of man-caused effects on a species. the Peregrine was removed from the Endangered Species List in 1999, after an extraordinarily successful recovery from the effects of DDT pesticide. Until 2015, it was intermittently monitored to maintain population information and to assure that the species is retaining its recovery success. The last survey in Big Bend National Park revealed a thriving and healthy population.
In the fire area, there is only one eyrie that is likely to have been directly affected by the fire. The East Rim Eyrie is near an area that burned and there was some spotty fire below the eyrie. Besides the fire itself, the helicopter use in the area for water drops over multiple days would have disturbed the falcons. If a pair were using the eyrie, they would have likely been in the active nesting/feeding phase and the fire and other disturbance could have caused them to abandon the nest. Visits to the area by two biologists have been brief and no peregrines have been seen, but it often takes hours of observation to see a single peregrine attending an active nest. Biologists will be watching once the post-fire monitoring is in effect.
The good news is that all other Big Bend area eyries are far away from effects of the fire and those populations should not be impacted. Also, the history of the eyrie is that it is a preferred spot, and even if disrupted in one year, the pair has returned the next breeding season.
If you see a Colima Warbler (Leiothlypis crissalis) in the United States, you must be in the Chisos Mountains. Even though they are found in a protected area (BBNP), the species is listed as Vulnerable in Texas. They arrive in April, nest and raise young into August, and then leave for the winter to Colima, Mexico. Birders from around the world visit Big Bend National Park to find these birds. There is a good article about them, complete with photos, on the park website at: https://www.nps.gov/bibe/learn/nature/bird-stories.htm. Thankfully, the fire occurred just as they would have been arriving and according to a knowledgeable biologist only about 20% of their habitat was affected by the fire. The wonderful thing about wildlife is its resiliency. Some of the habitat was impacted, but birds can relocate their traditional nest areas if other appropriate habitat is available before they begin laying eggs. If you are looking for Colima this July, read the article, ask at visitor centers in the park about reported locations, and go find a Colima!
None of the area burned is appropriate habitat for the Black-capped Vireos (Vireo atricapillus). Once listed as Endangered by USFWS, the species has been delisted because preservation and recovery efforts have been successful. The birds arrive in April, breed, and remain until July and then migrate to their wintering grounds in Mexico. The known vireo nesting habitat is not only outside the burn area, but far enough away that it will be little impacted. The known habitat is around the edge of the Chisos woodlands in areas where the montane forest begins to merge into mid-level trees and shrubland. In fact, vireo habitat benefits from burning and may become expanded with the regrowth of shrubby vegetation at the edges of the burn.
Hope
Most of the species of concern related to the recent fire are birds and mammals that, thankfully, are quite mobile and the populations are unlikely to be severely affected unless the fire is followed by other severe occurrences like the extreme drought of 2011 when little or no rain fell in the area for around 15 months.
Park Service is not only concerned with the species discussed here, but with the entire habitat and ecology of the High Chisos. There are numerous additional considerations and major complexities that must be considered. Fire is a natural occurrence in nature, but when dealing with small, protected areas and Sky Islands like the Chisos Mountains, more concern must be directed by managers toward properly controlling fire. Big Bend National Park has had a robust and active Fire Management Program for several decades and controlled fire has improved and protected the habitat. It is out-of-season, man-caused fires like the recent one that become concerning and potentially damaging to the park ecology. There will be significant monitoring and rehabilitation work done over the next few years to attempt to ameliorate the damage that occurred during the South Rim 4 Fire. That said, there is some damage that will take decades to repair itself and world-wide changes in seasonal heat and rainfall could significantly hinder any full ‘recovery’ of what the Chisos was prior to the fire.
Only time will tell.
Betty Alex, a fifth generation Texan, was raised in a small farming town in South Texas near Corpus Christi. She graduated from Corpus Christi State University (now Texas A&M at Corpus Christi) with a B.S. in Wildlife Biology in 1977. She worked for the U. S. Geological Survey for five years as a Sedimentologist and Biologist (her minor is in Geology). In 1980 she fulfilled a long desire to live and work in the Big Bend area of Texas by accepting a job at Big Bend National Park. She worked in the Ranger Division for over a decade and then accepted the Geographic Information Specialist position doing GPS and computer mapping and spatial analysis. After 22 years in that job, she retired in 2013. She now spends her time working on a project to organize several thousand photos from a Rare Plant project (2003-2007) and create a publicly accessible data base linked to the photos, working as a Volunteer In Parks for Big Bend National Park. She also spends time being a grandmother and great-grandmother.
Photos – cover and 5th from Top – Mathijs van Lisdonk Photography, Wikimedia Creative Commons
Top – Rick LoBello
2nd from Top – Brian Ralphs , Wikimedia Creative Commons
3rd from Top – Brian Ralphs , Wikimedia Creative Commons
4th from Top – Scott Altenbach , Bat Conservation International
Bottom – Alan Schmierer , Wikimedia Creative Commons
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