Flat-tailed horned lizard numbers boost
OCOTILLO WELLS — A recent survey of the flat-tailed horned lizard at the Ocotillo Wells State Vehicle Recreation Area revealed an apparent increase in the lizard’s population, suggesting increased rainfall may be driving the upward trend.
Although the lizard data recently collected by OWSVRA staff remains to be fully synthesized with similar data collected over the long-term by other federal and state agencies, it has created a stir among the state park’s environmental staff.
“We’ve had excellent numbers this year,” said Danny McCamish, OWSVRA environmental scientist. “Probably record-setting numbers.”
Yet, McCamish cautioned that recent survey data must be compared to long-term data collected at the regional level before any conclusions are made about lizard population trends.
As part of a multi-agency voluntary management plan, Ocotillo Wells state park staff have been conducting annual flat-tailed horned lizard surveys for the past four years, during which time data had suggested a gradual decline in the park’s population, McCamish said.
That trend reflects the tail-end of data collected over a span of 10 years by the Arizona Game and Fish Department.
Within that 10-year span, officials had taken note of a cyclical ebb and flow, where its population decrease appeared to have been exacerbated by the state’s historic drought, McCamish said.
“We’re looking at a snapshot of a snapshot in quite possibly the worst drought we’ve had in our time,” McCamish said, referring to the park’s recent survey data.
‘Mark and recapture’
During different parts of the year, OWSVRA staff will conduct separate occupancy and demographic surveys. The former will simply note whether a lizard is observed on a designated plot of land within an hour’s search, while the latter employs a “mark and recapture” technique aimed at determining the species’ reproductive health, lifespan and population characteristics.
During a 10-day period at the end of September and early October, the park’s environmental staff gathered for the second of its two annual demographic surveys, no easy task considering the lizard’s knack for blending into its surroundings.
“So much of this is what feels like sheer luck, as much as it is skill,” McCamish said. “It’s fun and grueling but it gives us a lot of interesting data about a species that we’re learning more and more about.”
The early morning searches get underway once ground temperatures rise to 20 degrees Celsius, or about 68 degrees Fahrenheit, perfect for drawing out lizards looking to bask in the sun and restore their energy levels.
When encountered, lizards will be temporarily marked with a magic marker, weighed and measured, have its GPS coordinates taken and its identifying number checked against records to determine if the lizard had been previously captured.
Adult lizards not previously captured will also be implanted with PIT (passive integrated transponder) tags, which are inserted into an empty space in the left side of their abdomen, according to practices approved by the multi-agency Interagency Coordinating Committee that sets the protocols widely used for such lizard surveys.
In the case of juvenile lizards that are too small to implant with a PIT tag, staff will carefully remove the first knuckle of a limb’s digit to establish a corresponding identification number that can range from a single digit to the thousands.
“I feel bad anytime we have to clip one of their fingers,” McCamish said.
By the end of the park’s two 10-day demographic surveys, conducted on two separate plots of land, environmental staff had encountered a total of 124 lizards, with 28 of those classified as juveniles.
Of those 124 total, 72 had been first-time captures, with the remaining 52 having been previously captured during the surveys.
Population dynamics
In contrast to the relatively large mammals who call the 86,000-acre park home, small mammal and reptile populations will respond quickly to changes in rainfall, said OWSVRA senior park aide Joni Bye.
Unlike other species of lizards, the flat-tailed horned lizard’s diet is made up exclusively of harvester ants, which depend on the presence of seeds and leaves for their survival.
The increase in vegetation found within the park results in more harvester ants, and, apparently, flat-tailed horned lizards.
“This is the first good year in about six years,” said Bye, who has been employed at the park since 2002. “It’s nice to see after seeing nothing for so long.”
On average, the state park receives about 3.3 inches of rainfall annually, the National Weather Service (NWS) reported. Between July of last year and this June, an estimated 4.43 inches of rain had fallen at the park, up significantly from the 2.1 inches it had seen during the same period a year prior.
The lizard is characterized by its broad, flattened tail and long, sharp horns on its head. Juveniles can be the size of a dime, while an adult can average about 3.5 inches in length from snout to the base of its tail. Unlike other lizard species that will run and hide when threatened, the flat-tailed horned lizard will often remain motionless, relying on its camouflage to help escape detection.
“Their only defense is to sit perfectly still,” Bye said. “They’re not real bright.”
The lizard’s habitat ranges from the Coachella Valley and Salton Sea to the northwest, eastward to the Imperial Sand Dunes Recreation Area, and southward into the desert of Baja California and Sonora, Mexico.
The lizard is considered a sensitive species in California by the Bureau of Land Management, while the state Department of Fish and Wildlife considers it a species of special concern. Neither designation provide it any specific protections.
Repeated attempts by the Center for Biological Diversity to list the lizard as an endangered species at both the state and federal level as a result of perceived declining population numbers proved unsuccessful.
In December, the state Department of Fish and Wildlife determined that voluntarily improving existing land management strategies and species monitoring and conservation efforts could have beneficial impacts no different than having the species listed under the state’s Endangered Species Act.
The lizard’s monitoring program at OWSVRA places a big demand on its staff, but provides the information needed to gain perspective into its population trends on a range-wide level, said environmental scientist Sara Lockett.
“We’d all prefer to be proactive and know what’s going on, instead of being reactive,” Lockett said.