A mountain yellow-legged frog hides immediately after being released

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Hopping Into Technology

That frog isn't easy to spot among those rocks! That's part of why we had to devise a plan to monitor this endangered species without relying on our eyes alone.

One of the most important stages of any conservation reintroduction program is post-release monitoring. While the reintroduction itself is an exciting aspect of our work—it is gratifying to watch captive-born, endangered animals explore their natural, wild habitats for the first time–it is very transient: the animals are in one place, then they’re in another.

Preparing the animals for release and finding out what they’re up to once they’re back out in the wild is often where the real work comes in. Without tracking and monitoring animals after releasing them, it’s hard to say whether or not these conservation initiatives are effective.

Mountain-yellow legged frog habitat in the San Jacinto Mountains

Mountain-yellow legged frog habitat in the San Jacinto Mountains, in Southern California.

Post-release monitoring and surveying can take many forms. Some scientists use either physical traps or motion-triggered trail cameras to keep an eye on their charges. Others use visual surveys or auditory surveys, listening for bird or amphibian calls. When funds are available and animals are sufficiently large, radio or GPS transmitters attached to collars or backpacks can be used to track individual movement.

For the mountain yellow-legged frog, an endangered species native to Southern California, many of these methods don’t work well. Physical traps would make frogs too vulnerable to predators. Camera traps depend on movement and heat signatures, so are not well-suited for tiny, ectothermic (“cold-blooded”) animals. Mountain yellow-legged frogs do not make calls, so they're difficult to hear, and they camouflage and hide in their habitat, so they are difficult to see. These frogs seem to be made to make post-release monitoring a challenge!

One of the microchips used to tag the frogs.

One of the microchips used to tag the frogs, called a Passive Integrated Transponder, or PIT, tag.

This year, the mountain yellow-legged frog program at the San Diego Zoo Institute for Conservation Research is trying something new. Every released frog is given a tiny microchip (about the size of a grain of rice), similar to the microchips used in your pet dog or cat. A grant from the Schwemm Family Foundation allowed us to purchase a new long-range microchip reader, which looks like a metal detector. Instead of beeping when it finds metal, though, it beeps when it finds a microchipped frog!

The microchip PIT tag reader

The PIT tag reader. There are five frogs hiding in this photo!

The first time we took the reader out in the field, we were worried. It’s hard to climb waterfalls while managing something that looks like a metal detector. There are boulders, plants, and logs everywhere, and we wondered if the reader would even be able to detect frogs amongst these obstacles.

A scientist uses the microchip reader

The microchip reader in use.

Minutes after beginning our first survey, the reader loudly beeped over a small rock in the stream. We put gloves on and gently lifted the rock. Crouched beneath it and looking up at us was one of our juvenile frogs (individual 181692, according to the reader).

Since finding 181692, we have identified and located hundreds of hiding frogs using the reader. It’s only been a month since the release, but this essential tool is now allowing us to re-identify frog individuals without having to rely upon vision, and without even having to capture or bother the frogs at all.

Conservation biology increasingly depends upon new technology like this. We are so grateful for generous donors like you who make these exciting leaps possible, and we’re excited to learn from all the data this reader will allow us to collect on the 231 frogs we’ve released this year. Stay tuned!

photos credits | Talisin Hammond

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