For the past several months, ACR’s Quinton Martins and Keysight’s Neil Martin have been developing a new walk-through cage trap that utilizes ultrasonic electronic sensors and has become ACR’s main safe-capture method. Because of trapping restrictions in California, or as an additional “tool” for biologists in other states or around the world, this cage design should be very useful. Some of the benefits include: no bait is necessary; researchers can trap all-year round with no seasonal limitations due to bait degradation; set electronic timer to have cage active only when capture teams are on standby; and researchers can set the ultrasonic electronic sensors to target size-specific animals, avoiding capture on non-target species.

The two presented the cage trap at the 12th annual Mountain Lion Workshop in Estes Park, CO.

Mechanical walk-through traps exist but have limitations
Walk-through cage traps have been proven effective for safely trapping leopards and cheetahs in Africa, and are particularly useful when bait is scarce, baits degrade quickly, or when animals are ‘trap-shy.’ These mechanical walk-through traps are, however, difficult to set to avoid capturing non-target species.

At ACR, we built a walk-through cage and tested it to see if mountain lions, like their African counterparts, would also walk through these unbaited cages set on trails. In 1 month we had mountain lions walking through unset cages nine times. We then developed a “high-tech” electronically operated cage which improves efficacy, reduces capture of non target species, while simultaneously minimizing trap management.

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How the trap mechanism works
The cage doors are held vertically in “U” channel guides and drop simultaneously when a solenoid actuator is triggered by ultrasonic sensors, pulling the actuator rods via a circular wheel, releasing the doors and then rebounding 2 seconds later to become the door-lock. The sensors are sensitive to animal height. We set the height so that only mountain lion-sized animals will trigger the trap. Two sensors are used, and need to both be activated further reducing non-target captures. We included a timer to ensure the trap was only active at night when capture staff could be on standby.

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Proof of concept
We tested the traps (with permission from CDFW) in our study area of Sonoma County. Within one week we had captured one adult male and one adult female in the new trap. No false triggers occurred, and several non-target species, including foxes and opossums walked through the trap without setting it off.

We plan to further develop this concept.