One Bighorn Sheep, Two Bighorn Sheep…
The day we have all been waiting for has finally come. After months of meetings, organizing logistics, applying for permits, and purchasing equipment, we are heading to Rancho Picacho, our base camp in the Sierra Juarez in Baja California. For the next few days we will capture 15 bighorn sheep to equip them with GPS collars and to carry out a genetic and health assessment.
Peninsular bighorn sheep occur from the San Jacinto Mountains in California south into the Sierra Juarez and Sierra de San Pedro Mártir in Baja California. Habitat connectivity between San Diego County and northern Baja California is becoming increasingly compromised by roads, the border fence, urban development, and incompatible public recreational use.
Bighorn sheep populations in southern California and northern Mexico have long been assumed to be isolated, but recent field surveys carried out by San Diego Zoo Global have indicated that bighorn sheep do use the border areas and likely move between the two countries. However, to successfully move from north to south sheep would have to cross four lanes of traffic on two major highways; I-8 in San Diego and Highway 2 in Baja California.
For the next two years, bighorn sheep equipped with GPS collars will provide us with important data on their movement in relation to habitat features such as roads, human settlements, and habitat oases. The biological samples collected will help us to describe the genetic structure and connectivity of the population across the border. They will also be used to test for different diseases to evaluate the health of the population. The recent pneumonia epidemic among bighorn sheep in the Mojave Desert shows the importance of health studies like these to better understand disease outbreak and interactions of wild bighorn sheep populations with domestic livestock.
The capture team included biologists and veterinarians from San Diego Zoo Global and the Universidad Autonoma de Baja California, as well as a crew that specializes in helicopter captures. The first day was spent getting the equipment ready and setting up everything. The veterinary and wildlife disease team transformed an old shack into a laboratory with clean work areas, centrifuges, and liquid nitrogen tanks to process and store all the samples for further analyses in the Wildlife Disease Lab. We discussed the plan with the capture crew for the next day: we will be targeting bighorn sheep in the northern part of the Sierra Juarez, close to the Mexican border.
The next day started early with a cup of hot coffee, eggs, and handmade tortillas. By sunrise the helicopter was ready to take off for a reconnaissance flight. Soon they spotted two rams and were ready for the first captures. With the helicopter flying only 35 feet above ground, the net-gunner leaned out the door and shot a large net over the impressive looking ram. The net tangled in the large horns, but the animal kept running. The second net brings the ram to a stop and a “mugger” jumps out of the helicopter to blindfold it, tie its legs and get it ready for transportation.
The captured bighorn sheep were transported by helicopter a short distance to a processing area where a wildlife veterinarian, who collected samples for disease and genetic studies, could examine them. Each animal gets fitted with a GPS collar that will record hourly locations and receives an ear tag that will allow identification during future aerial and ground surveys. After a short time the animals were transported back to the capture site and released. Without the blindfold that keeps them calm, they quickly run off and disappear into the rugged terrain of the Sierra Juarez.
It’s impressive to see the capture team at work. When the crew returned to refuel after about two hours of flight, they reported another two to three successful captures. By noon the next day we had successfully captured all 15 bighorn sheep. Everybody was excited that things went so smoothly, but I think that most of us would love to spend another couple of days in the field.
Mathias Tobler, Ph.D., Senior Researcher, San Diego Zoo Institute for Conservation Research.