The blunt-nosed leopard lizard was one of the first animals to be protected under the Endangered Species Act in 1967.
Since that time, the endemic lizard has disappeared in about 85 percent of its range and continues to decline.
Colloquially known as the “Valley Dragon,” it once inhabited a contiguous region along the Diablo Range where it overlaps with the arid San Joaquin Desert.
“Blunt-nosed leopard lizards originally inhabited millions of acres of the San Joaquin Desert, as well as the intermountain valleys nearby, such as the Carrizo Plain,” said Joseph Belli, a wildlife conservation biologist, and expert on both the lizards and the Diablo Range.
“They ranged at least as far north as Stanislaus County, and there’s a highly credible record of one spotted near Corral Hollow as recently as 1960. Today, it’s doubtful that any persist north of the Panoche region,” Belli noted.
Currently, the lizard exists only in isolated populations in the upland desert.
Many of these populations have been extirpated, and those that exist are facing alarmingly declining numbers.
One critically endangered population is on the Diablo Range’s Panoche Plateau.
Saving the Valley Dragon from Extinction
Newly released blunt-nosed leopard lizard entering burrow. Photo: Emily Sherwood
In 2020, a team from the Fresno Chaffee Zoo discovered that the population had declined precariously, facing possible extinction.
They received emergency permission to collect seven lizards to try to breed them in captivity.
Led by Dr. Rory Telemeco, Director of Conservation Science at the Fresno Chaffee Zoo, the captive breeding program has had some early successes.
Blunt-nosed leopard lizards in the lab. Photo: Laura Kindsvater
To date, zoo staff have reared 234 animals in the lab from the original group.
Beginning in 2023, a total of 118 blunt-nosed leopard lizards has been released into the wild over successive years. That is certainly a cause for celebration!
Dr. Telemeco and his team are still learning about how to raise the lizards to ensure they have the best chance of survival.
In November 2024, Save Mount Diablo funded a sophisticated weather station to provide environmental and climate data.
Installing the weather station on the Panoche Plateau. Photo: Fresno Chaffee Zoo
The weather station data helps the team understand factors critical for survival in the wild and replicate them in the lab.
Using the weather station data, the biologists running the program are learning more about how to rear the lizards to increase their survival rates.
In the wild, blunt-nosed leopard lizards have an average lifespan of about two years.
Yet in spite of the impressive release numbers, more than half of the captive-bred animals don’t survive their first year in the wild.
From the outset, about half of the lizards are lost to predation shortly after release.
Half of those that evade predation don’t survive their first inactivity period, and only about 25 percent of the cohort make it to adulthood.
One important measurement from the weather station is the temperature of the underground burrows where the lizards spend their inactivity period.
Many reptiles spend colder months underground in burrows in an inactivity period similar to hibernation.
The blunt-nosed leopard lizard spends over half of its life in inactivity from July through April.
During this time, cooler underground temperatures reduce the animal’s body temperature and metabolic rate and decrease its energy depletion.
Environmental Data Drives Adaptive Management
The weather station data is already helping zoo staff to better understand natural underground conditions and replicate them in the lab.
Measurements indicated that underground temperatures where the lizards overwinter range between the high 40s and low 50s Fahrenheit in the winter.
By adjusting temperature in the lab to better match natural habitat conditions, the lizards have shown better dormancy survival rates.
The hope is that the same results will decrease mortality when the newly released lizards enter their first inactivity period in the wild.
“We’re trying to replicate natural rearing conditions to produce animals that are best equipped to thrive back in the wild,” said Dr. Telemeco.
Achieving Population Stability
Future generations could help stabilize dispersed populations. Photo: Laura Kindsvater
Another critical step in reviving the Panoche Plateau population is getting them to reproduce in the wild.
“We will continue reintroductions until 50 or more natural-born females successfully reproduce for three consecutive years,” explained Dr. Telemeco.
The team has observed courtship behavior in the released lizards but have not documented reproduction and are trying to understand why.
Reproduction may be linked to energy state; if the animals aren’t finding enough prey, that may inhibit mating. Other factors may be inbreeding or climate conditions.
When the Panoche Plateau population becomes self-sustaining, Dr. Telemeco’s team plans to expand their rewilding work across other populations.
Their goal is to not only help arrest the decline but also apply the lessons learned to other populations and further help this critically endangered species to thrive in its native habitat.
