Tap dancing tamales

Last week, I encountered a mystery that was best solved with a tamale. (I wish I could say that every day.)

One of my research projects this summer involves using game cameras to capture candid videos of small rodents eating seed bait using infrared flash. I had placed a ten of them in the field for nearly a week, and while the seed bait was gone, no videos recorded the culprits.  Well, we did have two videos of a ground squirrel one afternoon. But that left a lot seeds unaccounted for. And I did have a lot of video of wind blowing branches around, so the cameras were clearly functioning.

The seeds in question were large enough that I was skeptical of ants being responsible for their theft. And there was one more key piece of the puzzle: despite the fact that most of the small granivorous (seed eating) mammals in this area are nocturnal, I had no night time videos.

I had previously captured regular videos of wood rats, deer mice, and pocket mice in these environments eating such seed bait. What was the difference this time?

I realized it might have to do with the orientation of the cameras. While the distance to the bait was the same as before, I had secured the cameras above the bait to record downward, having read about a study from Australia in which downward orientation improved the reliability of triggering, increased the researchers’ ability to identify animals, and also provided more rigorously defined study areas and rates of animal movement.

However, these rocks are much hotter than body temperature, and take a long time to cool down.  Heat absorbed by dark volcanic rock throughout the course of a hot, arid foresummer day is familiar to me and to my field assistants. On some of our epic experimental set-up days, we laugh about how by 11am we stop sitting on rocks because they burn our backsides through our pants, by 1pm we can no long pick up small rocks to use as tools, and by 3pm they burn our feet through the soles of our shoes.

These game cameras are built generally with spotting deer at forty feet, not mice at three feet. Some of the issues with this off-label use are cheaply remedied by, for example, placing masking tape over the panel of LED flash to reduce the blow-out of close objects. It seemed likely to me that the heat-sensing motion trigger used by the camera after dark cannot “see” the rodents moving against such a hot background.

A series of tests were in order to confirm this hypothesis, but we needed some rodent stand-ins. Being Tucson, I had a dozen frozen tamales in the freezer, which seemed about the right size.

We commenced a series of trials of triggering the game camera using a microwaved tamale moving across the field of view, varying the tamale temperature and distance from the camera. These tests were conducted at first in the darkened back closet of the secret underground laboratory in the corner of the sub-basement of Biological Sciences West. I later repeated some trials with the tamale dancing before the camera in varying orientations that night in the field.

I am still looking for a journal in which to publish these groundbreaking results. In the meantime, for your entertainment, I give you a sample of my tap dancing tamales recorded in infrared.

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