Bounty -- A Month in America’s Southwest Seeking to Understand Carnivores

A Palo Verde (Parkinsonia florida) in Saguaro National Monument with petals blanketing the wash below, indicating heavy pollination, a healthy insect population and plenty of leguminous fruits.

About four weeks of the long desert year the Gila Monster makes it aboveground to search for eggs, sleeping things, and things more slow than it. A rattlesnake pushes venom like a syringe into its victim but a Gila chews to release the poison. Every gnawing adduction finds a little more toxin into the meal and with jaw muscles proportionally larger than a pitbull it doesn’t let go easily either.  After digesting, the prey becomes a precious fat hidden away in the Monster’s tail that will sustain it for months at a time. For a lizard that moves at a top speed of one and a half miles per hour, barely sees the sun in a place renowned for sun, and has skin intermixed with small pieces of bone, each successful meal is a substantial victory.

Becoming food for something else trying not to be food in the desert is part of the deal. There is a net biotic loss annually and it is a miracle of geologic patience that life abounds. The constant struggle between harsh environmental entropy and the imperative for existence found in every living organism is at a particular crossroads in the desert, any desert. The Sonoran Desert of North America’s southwest has a strategy to combat perpetual threats of non-existence: bounty. Day-to-day and year-to-year the dry heat wins but with the help of bi-modal rains and the fact that every few years the cycle of exceptionally good conditions will produce a bumper crop of new sprouts, new flowers, new seeds and new life. After that the cycle begins anew and insects proliferate the lizards to snakes to mammals and into the crop of the vultures and then back into the soil that barely is. That abundance sustains the ecosystem with a pulsing vigor of life that pushes into each level of the food web.

This is by no means saying that the desert is dead, barren, or, well, deserted.  Life is choc-a-bloc around the indicator species such as octogenarian Saguaros, fertile Palo Verdes and the refuges of Cholla. The five  seasons of the Sonoran (Winter, Spring, Foresummer Drought, Summer Monsoon, and Autumn) drop at least two different kinds of rain, the equipatas –or “little packages”-- in winter and the downpour of las aguas during the monsoon. Those waters, plus the El Niño years of torrential flooding, move water through innumerable washes and strike down columnar cactus for decaying fertility with gale winds. But the seasons also desiccate voraciously and what doesn’t dry gets burnt or buried.

In the interim between the chubascos (an extremely violent tropical storm in the Sonoran) how does the desert ecology not death spiral into unchecked herbivory, fought off only by ever-larger cactus spines and formic acid? In essence, the question for me is how is the desert not more “deserty”? Growing up on the western Californian edge of the Sonoran, I came to define the desert by the things that tried to hurt me and eat my soccer balls as a kid: spines, thorns, and heat. In addition to the dust, fangs and poison the difficult question is what is keeping it in check? In a place as harsh as the desert where you fight a losing battle except for the glut of a good year, what is keeping the Red Queen of perpetual plant and animal nastiness distracted?

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The one Gila Monster seen during the field work. Strolling around, it quickly found its way under a creosote bush and away from prying humans.

One of the many rattlesnakes trying to blend too easily into the surroundings. This one, like almost all the other ones I encountered, decided not to rattle until after I almost stepped on it, seen it only at the last minute, and averted my boot quickly.

Some of the more spectacular paradigms that have emerged from conservation science in the last couple decades are the ideas and refinements of ideas on trophic cascades, keystone species, and niche partitioning. Essentially they boil down seemingly toward a paradox: predators are the protectors of bounty. An animal built with steak knives in its mouth and on its paws doesn’t seem to be the likely image of a beneficial organism, of an animal actually helping the system. However, in the desert, as in most other habitats, the predators promote the bounty.

Imagine being a vegetarian where all of your food sprouts from the ground and is all around you. Yes, it is relatively sparse and you have to fight some thorns to get to it but basically you can walk around in this eden carelessly and pick what you want from the best plants you can find. If you found a particularly great area you would spend time mowing down everything green you could see until your belly hurt. Now imagine that you hear some rustling in those bushes or you smell something faintly musky. Are you going to take the chance and keep eating this great plant you found or are you going to make use of those marathon sprinter legs you have and get the hell out of there? This is the essence behind the green world and ecology of fear hypothesis: more potential threat of teeth means more movement which means more green things. 

Let’s play another game. This time imagine you are a bird/reptile/rabbit/something small and as a toddler you are told that many generations ago there were many more of your kin. There were also these ferocious giants lumbering around but you really wouldn’t have to worry about them because you are so fast that they only occasionally become a threat. These monsters haven’t been seen for a while but instead there has been an invasion recently of these smaller things (raccoons, rats, feral cats, etc) with teeth and claws that make eggs and infants their favorite meals. They roam around all over the place and you have to watch out for them because every single one of your brothers, sisters, cousins, and their homes have been destroyed by this hoard. With a few more technical details, this is the idea behind mesopredator release. When the big animals disappear what they feed on is ‘released’ unchecked and can decimate populations of what they then feed on. This is further exacerbated by the introduction of fecund non-native species or people who keep their house cats outside of the house.

Understanding the places in the food web each of these animals fills is called niche partitioning. Or another way: the tenuous relationship that animals have when they are in the same level of the web but have specialized enough so as not to compete with each other. Niche partitioning helps allow the desert bounty to exist and flourish.

A seemingly endless sky preparing to push its clouds together for one of the afternoon showers we were blessed with to help dissipate the 100 degree heat.

The bounty as I am calling it here is biodiversity and species richness; or: the amount of different kinds of life. The Sonoran exhibits a unique desert with a particularly large amount of life partially because of the combination of a variety of habitats: Tundra travel to their lowest latitude here while Tropical Rainforest travel to their highest as they meet unique Sky Islands of the immensely tall mountains. According to the Arizona-Sonora Desert Museum “[all] of the world’s biomes occur in the Sonoran Desert Region.” More different habitats create more edges and more edges create more overlap with which species are required to adapt uniquely. Threatening the bounty is an unchecked cycle of non-native plant invasion elbowing out native flora, herbivores with little fear of predators grazing too long and denuding new plant growth to moribund nubs, and a subterranean water table drained too deep for critical oasis refuges by human use. These are but three of the threats but habitat fragmentation, urbanization and human encroachment are a few more. All of these impact, directly or indirectly, the carnivores, the directors of how everything else moves.

For most of the month of May, I spent my mornings hiking around southern Arizona taking pictures of fox prints, deer scat, bird nests and rattlesnakes while paper-bagging all the carnivore feces we could find. Starting at dawn but finishing our work before the sun really started to flex its early afternoon muscle, we would check five sites a day searching for any vertebrate presence within a fifty meter radius of the site’s center. To find presence we utilized several strategies. First and most important is positioning the movement-sensor camera angled toward the dollop of foul-smelling cat food dropped on a rock. Whatever tries to make that cat food breakfast secretly gets caught on the camera (actually, anything that moves within range gets caught: each SD card has about ten thousand photos of grass swaying in the wind for every Grey Fox stalking the discarded Friskies pate). The second method involves randomly placing throughout the transect two-foot squares of aluminum dusted with activated charcoal encircling a healthy portion of more cat food. As an animal is helplessly drawn toward the aroma it lifts the charcoal from the aluminum like a police investigator taking prints but in reverse. We can then tell what vertebrate beat the omnipresent ants to the free meal from its incriminating paws. Last comes the poop collection. While we documented each and every kind of poop we bagged only the carnivore droppings. It is difficult to imagine a better way of discovering what kinds of prey and predators exist in an area than by identifying a poop by its maker and the poor creature that helped make it. Unfortunately for us researchers that means walking out of the desert with bags of feces. 

This project was designed by University of Louisiana at Lafayette PhD candidate Ange Darnell.  She is looking at carnivore niche partitioning: where and how a carnivore eats and lives in a food web. Following in the footsteps of the conservation biologists who unearthed keystone species and trophic cascades, the conservation implications of her study will help habitat managers understand the full impact of carnivore species within the southwest. 

Ange is working to understand carnivores. She is equally at home in the field hiking the distance to set up her sites as she is expertly explaining niche partitioning to her eager volunteers. As a researcher with a passion for teaching and encouraging others’ engagement with natural history and conservation study, Ange would eagerly pick up a field guide after each work day and share the day’s rare species or help identify the unknown bird call. 

Above, Ange has provided a slideshow of animals captured on the motion sensor cameras at each of the sites. You will all kinds of behoviours including a lion passing through, a coyote feeding on cat food, a curious javelina, and a defecating grey fox.

Ange represents to me what is so special about the conservation profession. She is a highly intelligent individual that exhibits her passion for not only understanding the natural world but also sustaining it through diligent and deductive work; yet, she is not blind to the real-world challenges and constraints. Open-eyed, she is propelled by an inner fire but has the patience and desire to ensure that the approximately 50 different volunteers she has organized are engaging fully with the importance of the work.  The combination of passion mixed with brilliance, grit with sensitivity, creativity with logic, ruggedness with mental flexibility, and empathy with objectivity are some of the baseline attributes a conservationist needs to work from, as Ange certainly does.

As a university researcher and lecturer, Ange uses her skills to teach others whenever possible. In the picture above, she is showing the team how to handle a pocket mouse that found its way into the camp.

On one of the first days of my time with her team, I was fortunate to see a Gila Monster – the only one seen during her year of field work. Rare as they are I knew it was a blessing and an opportunity to see how it lived effortlessly as I was standing there motionless yet still sweating through my shirt. It crawled over the yellow duff of fallen Palo Verde petals into the bramble of Creosote attempting unsuccessfully to hide its pink and black body.  We took some photos and I continued with my work knowing that the rest of the month held many more gifts. Ange’s team still has several more months of work and they’re still out there during the hottest part of desert’s seasons. I finished my month but I was right in knowing that it would be a month full of surprises and new knowledge. I narrowly escaped rattlesnake bites; saw my fair share of coyotes, hawks, and lizards; was continuously punctured by chollas, opuntias, and devil’s claw fruits; and learned how abundant an ‘empty’ desert can be. I’m excited to see the results of Ange’s efforts so that hopefully she can quantify the abundance and how the coyotes, lions, foxes and many more species are contributing to that bounty. 

To see more of my photos of the month, visit my Flikr: 
https://flic.kr/s/aHskaucMqR