By measuring the insulative capacity of active red squirrel nests KRSP researchers were able to provide the first empirical test of the heat dissipation limit hypothesis in the wild.  This hypothesis states that a female’s ability to provide nutrition for her pups might be limited by her ability to dissipate heat.  Consistent with this hypothesis, KRSP researchers found that lactating red squirrels used less insulated nests under conditions of potentially high heat stress.

Murray Humphries was interviewed about this research on Quirks and Quarks (link).