Studying snakes without rattling them? There’s now tech for that

Monitoring and keeping track of snakes is a cumbersome task. Jeff Lemm knows the inefficiencies all too well. The herpetologist has been studying red diamond rattlesnakes (Crotalus ruber) for years. In the early 2000s, he radio-tagged a few of the pit vipers in a bid to trace their movements. Since snakes don’t have appendages, the telemetry radios had to be surgically implanted, giving rise to time-consuming challenges.

“Snakes have to come in and out of anesthesia, and there is a risk of infection,” Lemm, conservation program specialist at the San Diego Zoo Wildlife Alliance (SDZWA), told Mongabay in a video interview. “You have to time it out so that you get the radios back in time before the battery dies, or else you would lose the snake.”

Now, Lemm is working to reinvent how snakes are monitored and studied.

He and his team at the SDZWA have collaborated with researchers at San Diego State University on a way to use tiny and noninvasive transmitters and accelerometers to study snakes. The transmitters can be attached to the base of the snake’s rattle, while the specially designed accelerometers are attached near the animal’s neck.

“It is a game changer not having to catch the animal and bring it to the vet and wait for it to recover,” Lemm said. “We could do it right there in the field and get the snake back out and moving in half the time.”

Red-diamond rattlesnakes are a large and venomous species native to southwest California in the U.S. and Baja California in Mexico. As predators, they play a vital role in the ecosystem by keeping rodent populations in check. A 2018 study also explored the role of rattlesnakes as potential secondary seed dispersers when they feed on rodents that carry seeds.

Classified as a “species of special concern” in the state of California, red diamond rattlesnakes have faced increasing threats from habitat loss as well as from being struck by vehicles when attempting to cross roads. They live either in the desert or in coastal sage scrubs, the latter being prime development habitat. “Right off the bat, they have trouble because they have such a small home range and then, secondary to that, they live in a very endangered habitat,” Lemm said.

The nature of the animal’s habitat also makes monitoring them all the more challenging. With coastal sage scrubs being very dense and filled with rocks, spotting the snakes visually without scaring them off is a hurdle. It’s also hard to place camera traps in the ecosystem without getting them obscured by bushes. Even without these habitat challenges, studying these snakes would still be hard, researchers say.

“They are extremely reliant on camouflage and crypsis,” Rulon Clark, a biology professor at San Diego State University who co-led the project with Lemm, told Mongabay in a video interview. Red diamond rattlesnakes are also capable of remaining inactive and immobile for a long time. “If you sit there and try to watch them, they just freeze,” Clark said. “If you’re close enough to sit and stare at the snake, you’re scaring off all the small mammals or other things that might be around.”

The new technology deployed by the team aims to study the snakes without these intrusions. Since early 2023, the researchers have tracked 17 snakes using noninvasive radio transmitters and accelerometers.

The radio transmitters keep them informed about each snake’s location so they can find it at a later stage. By doing so periodically, they can also build up a map that helps them better understand the animal’s home range. They also measure the snake’s body temperature using an infrared thermometer, and document key details such as the height and species of vegetation in the region, ground temperature, air temperature, humidity and barometric pressure. “We need this data to help us figure out a lot of things: When are these snakes most active? What’s their ideal basking temperature? When do they move? At what time of the year?” Lemm said.

The accelerometer, meanwhile, records the animal’s movements in 3D. The team uses this data to map movements and link it to behavioral patterns such as mating as well as foraging. For example, “when a snake strikes, it goes from being still and coiled to extending its body very quickly, and pushing the head forward,” Clark said. “We’re able to see the acceleration of the device during that rapid forward motion.”

Similarly, the accelerometer can detect changes in a snake’s body movements when it swallows a prey and pushes it down into its body. By virtue of being located on the animal’s back, “it creates this unique kind of signature movement that indicates “Oh, some big carcass just passed under this thing,” Clark said. “We then know that the snake was able to swallow something, not just strike it.”

The team has used human observations and data from hidden cameras to corroborate and validate the findings from the accelerometers, following which they train a computational model to automatically detect and classify behavioral patterns based on the accelerometer readings.

Clark said the team wants to gather more ground-truthing data that will help them build a validation model that can detect reproductive behavior and mating rituals. “The movement is so stereotypical and so different from what a snake would otherwise do,” he said. “The two males will rear straight up and start waving back and forth while trying to push each other. It should be an incredibly unique acceleration signature that can easily be validated by our modeling process.”

As they continue to gather more data and improvise the technology, Lemm and Clark said they hope their work in tracking and studying red diamond rattlesnakes can serve as a case study for scientists around the world.

“Snakes are globally distributed in all the world’s ecosystems, and are a type of animal that is an important predator around the globe,” Lemm said. “I hope the tools we’re building here would be picked up by others to be able to apply for other snake species as well.”

Banner image: Red diamond rattlesnakes, native to southwest California in the U.S. and Baja California in Mexico, are important predators in their ecosystems. Image by San Diego Zoo Wildlife Alliance.

Abhishyant Kidangoor is a staff writer at Mongabay. Find him on 𝕏 @AbhishyantPK.

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Citation:

Reiserer, R. S., Schuett, G. W., & Greene, H. W. (2018). Seed ingestion and germination in rattlesnakes: Overlooked agents of rescue and secondary dispersal. Proceedings of the Royal Society B: Biological Sciences, 285(1872), 20172755. doi:10.1098/rspb.2017.2755