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UW Researcher Studies Factors That Could Affect Wyoming’s Horned Lizard Population


October 3, 2013 — They can flatten like a pancake and puff out their armor-like hide for protection. They can use their heads like a drill to dig a hole and burrow, or catch rain in their scales for drinking water. They are one of the few reptiles that give live birth rather than lay eggs. And they can even shoot blood from their eyes to fend off their canid predators.

Greater short-horned lizards may not be super heroes, but they’re pretty cool, nonetheless, says Reilly Dibner.

Dibner, a doctoral candidate in the University of Wyoming’s program in ecology in the Department of Zoology and Physiology, has been studying Wyoming’s state reptile for three years. Specifically, she’s studying a number of factors -- diet, development and predators -- that may be affecting horned lizard numbers.

Horned lizards, often referred to as “horny toads” because of their resemblance to the amphibians, are tied to specific resources. This means they are more likely to be affected by the loss of a particular host plant, favored prey or required soil type.

“I’m looking at a number of different factors limiting them,” says Dibner, whose research is funded by the Wyoming Governor’s Big Game License Coalition, the Wyoming NASA Space Grant and several departmental fellowships.

Dibner says one of the most striking specialist traits of these lizards -- of which there are eight species in the United States and an additional six found only in Mexico -- is that they prey exclusively on one or two types of ants. However, Wyoming’s horned lizard expands its menu a bit, as it has a taste for many types of ants (there are more than 90 species in Wyoming alone) and also feeds on beetles.

“Typically, horned lizards are dietary specialists, really picky kids in the candy store. Some horned lizards just like green or yellow M&M’s,” Dibner says. “The greater short-horned lizard is more likely to eat all kinds of M&M’s and maybe some Skittles.”

Dibner knows this through examining the contents in samples of the lizard’s scat. She also clips the claws on some adult lizards. The clippings can be used for an isotope analysis to also help understand the reptile’s diet.

Dibner theorizes that their less picky palate is one reason that the greater short-horned lizard has a wider range than other species of horned lizards. A Horned Lizard Conservation Society newsletter includes a map that shows ranges for the eight species of American horned lizards. According to the map, the range for the greater short-horned lizard is by far the largest, running from southern Alberta and Saskatchewan, Canada, through Montana, Wyoming, Utah, Colorado, Arizona, New Mexico, Texas, and into parts of Mexico.

Greater short-horned lizards prefer sagebrush, short grass and prairie. While such habitat is abundant throughout Wyoming, it doesn’t necessarily mean horned lizards are everywhere that particular habitat exists, Dibner says.

“The numbers are very sparse. I’ve found nearly 400 at a total of 100 plots in the state,” she says. “If lizards were there, there were ants. But, in some locations, if there were ants, I found no lizards. Ants are necessary for lizards, but not sufficient for presence (of lizards).”

Development deliberations

Dibner also has looked at development as a piece of her research puzzle. Because oil and gas development in abundant in the state, she has dedicated time analyzing in and around the Jonah Field, a large natural gas field in Sublette County that is managed by the Bureau of Land Management (BLM).

Greater short-horned lizards in Wyoming average about 2.5 inches -- from snout to vent -- in length and weigh a half-ounce. Larger ones can reach 5 inches in length and weigh an ounce. “I’ve found, in the densest areas of development, there’s no sign of lizards,” she says. “As for ants and beetles, there was no detectable difference from many other sites.”

One mile outside of Jonah Field, where there is no oil and gas development, a number of her reference plots contained healthy lizard populations. In areas of lower development or closer to the oil field, she found fewer lizards, but not significantly less.

“Why wouldn’t they be there? That’s the million-dollar question,” she says. “One possibility is just the increase of humans or activity elevates their (lizards’) stress response.”

However, Dibner has drawn no concrete conclusions so far. She is not sure whether there were no lizards in the Jonah Field to begin with or whether the reptiles moved when drilling began there.

Greater short-horned lizards, which live four to five years in the wild, typically only move 10-25 meters a week, Dibner says.

“I’ve recognized some adults that have only moved 50 meters within the last two years,” she says.

That recognition comes from checking tiny brands she placed on one or two scales of each lizard. To do this, she used a miniature “hot rod” typically administered during human eye surgery.

Even though she has identified roughly 400 lizards at her various plot points, Dibner says there are no concrete estimates of how many actually exist in Wyoming. When she talks to people, including ranchers she meets at her field sites, she says the response is usually the same: Folks remember seeing the horned lizards frequently as kids, but not so much now.

Dibner doesn’t know if that means there are fewer lizards now or that adults just don’t look for the reptiles like children do.

Still, the Wyoming Game and Fish Department has listed the greater short-horned lizard as “a Species of Greatest Conservation Need.” This means a particular species may be secure at present but, because it has limited distribution and is confined to a particular place, it could be vulnerable under large-scale changes.

A show of resilience

Despite Dibner’s concern about their current and future numbers, the little reptiles aren’t exactly helpless.

“I’ve seen a picture of its scales penetrating through a rattlesnake’s neck,” she says. “The lizard went from an armored pancake to a puffer fish.”

Their gray, yellow and reddish-brownish color allows them to camouflage themselves into the landscape from known predators, including birds, coyotes and foxes. They can shuffle their heads from side to side to tunnel into the ground, where they can burrow themselves from threats or hibernate, which they do from the end of September to late May. And, if they do get caught in a canine predator’s mouth, the lizard, as a last resort, can squirt blood from its eyes -- something that leaves a nasty taste in the animal’s mouth and often allows the reptile to escape.

The horned lizard may have an intimidating dragon-like appearance, but they are actually docile and non-confrontational creatures, Dibner says.

Dibner says they may squirm around in your hand at first, but you can stroke the lizard’s head and it will close its eyes, much like the relaxing effect a dog feels when one rubs its belly.

Dibner spreads her knowledge about the lizards around the state as part of UW’s Science Posse, which pays her stipend. In time, Dibner plans to submit her research to the Journal of Herpetology and Herpetological Review for publication consideration.

“They’re such unique, hardy creatures,” Dibner says. “That’s how we have to be. We’re a state of hardy individuals.”

Photo:
Reilly Dibner, a Ph.D. candidate in the ecology program in UW’s Department of Zoology and Physiology, is studying how diet, development and predators may be affecting greater short-horned lizard numbers in Wyoming.  (Gregory Nickerson Photo)

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