Thermal cameras, for instance, focus specifically on 10-micron radiation: the slice of the spectrum that most closely corresponds with heat released by living things. By measuring the stripes, Dr. Baker found they were tuned to 10 microns as well — apparently homed in on life’s most common heat signature. “That was my Eureka moment,” he said.
He found the same spacing in the equivalent hairs of a number of other species, including shrews, squirrels, rabbits and a small mousy marsupial called the agile antechinus. The antechinus hair in particular suggested “some really sophisticated optical filtering,” starting with a less sensitive absorber at the top of the hair and ending with patterns at the base that eliminated noise, he said.
As these hairs are distributed evenly around the body, their potential infrared-sensing powers could help a mouse “spot” a cat or owl in any direction, Dr. Baker said.
Dr. Baker’s hunch that these hairs help small mammals perceive predators is “plausible,” said Helmut Schmitz, a researcher at the University of Bonn in Germany who has investigated infrared-detecting mechanisms in fire beetles. (These beetles use organs in their exoskeletons to sense the radiation, which leads them to the recently burned forests where they lay their eggs.)
But jumping straight from structural properties to a biological function is risky, he said. To show that the hairs serve this purpose, it is necessary to prove that the skin cells they’re attached to are able to recognize very small differences in temperature — something that has not been observed, even though these cells have heavily been studied, Dr. Schmitz said.
Dr. Baker has continued to look into this question, designing his own observational tests. (One recent endeavor involves filming how rats respond to “Hot Eyes,” an infrared emitter he built that mimics the eyes of a barn owl.) As these experiments were not controlled, they were not included in the published paper. But now that he has lit this metaphorical torch, Dr. Baker hopes to pass it to others who can look deeper into these anatomical questions, and design more rigorous experiments.
“Animals that operate at night have secrets,” he said. “There must be a huge amount we don’t understand.”