The digit is less than half the width of other digits, and hence is vulnerable to injury and poorly suited for bearing load.
Infrared Thermography (IRT) was used to scan eight aye-ayes housed in San Francisco Zoo and Duke Lemur Centre as they foraged, and it was found that the third digit was typically 2.3 C cooler than other digits, but the temperature increased significantly when it was flexed to accommodate active tap-scanning and probing. Some individuals even showed a whopping 6 C difference in the temperature of their third digit.
|The temperature of the third digit prior to foraging: 26.9 C. The image shows that the middle finger appears dark on an IRT. Image: G.L. Moritz, N.J. Dominy|
|The temperature of the third digit during foraging: 29.6 C. The image shows that the middle finger appears as the same color as other parts of the body on an IRT. Image: G.L. Moritz, N.J. Dominy|
The thin and elongate morphology of digit III results in a relatively high surface-to-volume ratio. Because such a ratio is unfavorable for heat retention, controlled vasoconstriction is expected to reduce thermal costs during inactivity or locomotion.--Gillian L. Moritz and Nathaniel J. Dominy, DOI: 10.1007/s10764-011-9575-y
"Like any delicate instrument, it is probably best deactivated when not in use," Ms Moritz told BBC Nature.
The aye-aye is listed as Near Threatened by the International Union for Conservation of Nature (IUCN). Saving the species is no easy task, because superstition in Madagascar describes the primate as the harbinger of death. It is believed that whoever that is pointed at by the middle finger of this creature will die. When spotted, the animal is often killed and hung upside down so that the evil spirit will be carried away by travellers.
Thermal Imaging of Aye-Ayes (Daubentonia madagascariensis) Reveals a Dynamic Vascular Supply During Haptic Sensation. Gillian L. Moritz, Nathaniel J. Dominy. INTERNATIONAL JOURNAL OF PRIMATOLOGY.