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Quinton Martins, the leader of the Mountain Lion Project at the Audubon Canyon Ranch (ACR) in Northern California, had a problem. Mountain lions needed to be trapped and GPS-tagged for research, but traditional trapping methods were just not effective enough.
Trapping method of the past
The traditional technique for trapping mountain lions involves the use of a one-door “single- ended” cage, with bait to lure the cat inside. A mechanical pressure plate on the cage floor triggers the door-closing mechanism. There are two significant issues with this approach.
- Bait isn’t tempting enough. Where food is abundant, mountain lions may not be hungry enough to venture into a cage. It can also be very difficult to source mountain lion munchies, like roadkill deer.
- The wrong animals are caught! Often smaller animals like foxes and bobcats end up in the traps instead of mountain lions.
Catching more mountain lions
Mountain lions commonly re-use the same walking paths, so Quinton is able to use bushes and sticks to ‘funnel’ the animal into a walk-through cage that is open at both ends. This works well because it is far easier to convince a mountain lion to walk into a cage if it can see a clear path through the other side. It also eliminates the need for bait by taking advantage of the mountain lion’s natural walking path.
The challenge was to develop a reliable electronic system that would simultaneously close both doors of the walk-through cage while the mountain lion was inside.
In this new design, the doors operate very simply. They are held vertically in “U” channel guides and drop when actuator rods are pulled (Fig. 1).
Fig 1: Mountain Lion Cage Operation
A single, high-power solenoid pulls a wheel, which is connected to both actuator rods. The electrical system is controlled by an Arduino Uno microcontroller and a high current relay to activate the solenoid (Fig 2).
Fig 2: The prototype actuator mechanism
The system needed to detect the motion of a mountain lion without trapping smaller animals. I investigated several options for sensing mechanisms including a horizontal light beam sensor and ultrasonic range sensors. The light beam sensor worked, but it was difficult to set up and align and involved hanging wires over the side of the cage. I ultimately decided to use less intrusive ultrasonic range sensors installed at the top of the cage.
The system needed to detect the motion of a mountain lion without trapping smaller animals.
By measuring the distance from the top of the cage to the animal, we could set it to trigger on large animals only (mountain lions are typically at least 20 inches tall at their shoulders). The system was designed with two range sensors spaced 14 inches apart that would trigger only when both sensors detected an object at least 20 inches tall. This double-sensor set-up minimizes the chance of triggering on a smaller animal, such as a fox, that might sniff the top of the cage with its nose. If that happens, the small animal would only trigger one of the sensors, so the doors would not close.
The system was designed with two range sensors spaced 14 inches apart that would trigger only when both sensors detected an object at least 20 inches tall.
Debugging & deployment
With the basic design established, the next challenge was to write and debug the code controlling the actuator mechanism, which proved to be challenging. Incorrect timing caused the ultrasonic sensors to interfere with each other. We needed a way to debug the trap while in the field - the Keysight 1000 X-Series low cost oscilloscope proved to be just the right tool. The 2-channel oscilloscope allows the signals from both sensors to be viewed simultaneously, enabling us to adjust the timing and ensure reliable operation.
We needed a way to debug in the field – the Keysight 1000 X-Series Oscilloscope proved to be just the right tool.
Figure 4: Quinton Martins, (Ecologist - in the cage!) and Neil Martin setting up the trap in the field (Picture by Jim Codington)
Mountain lions have very large territories, so patience is required when trapping these elusive animals. After about two weeks, the waiting paid off, and we trapped our first mountain lion with this system, a female, and then caught a male 2 days later!
Figure 5: Trapped Female Mountain Lion
By Neil Martin
More information about the ACR Mountain Lion project can be found here:
Neil Martin is Keysight’s Corporate Marketing Director. He used to be an R&D engineer and he can still remember a little engineering - which he makes use of in his spare time for volunteer projects.