No. 77: Sep-Oct 1991
"The aye-aye, one of the strangest and rarest species of primates in the world, has an equally unusual method of finding food. Zoologists have discovered that it taps wood to locate cavities under the surface. Its skills are so well developed that it can tell holes containing grubs from those that are empty. It is the only mammal known to use such a technique."
To improve the efficiency of its "percussive foraging," the aye-aye has evolved huge bat-like ears and a highly elongated middle finger on each hand. This specialized finger does the tapping and the big ears relay the nuances of sound to the brain. So sensitive is this specialized form of sonar that the ayeaye can detect grubs 2 centimeters below the surface of the wood. Once a grub has been located, the aye-aye tears into the wood with its forwardcurving, chisel-like teeth. The incisors are remarkable for a primate, for they keep on growing, just like those of rodents. When the grub-containing chamber has been reached, the long, narrow middle finger is inserted and the grub is retrieved. A neat combination of attributes.
What is even more interesting is a comparison of the aye-aye with many of the woodpeckers. Many woodpeckers also employ percussive foraging, have special bills for chiselling, and possess very, spiny tongues for extracting grubs. In other words, the aye-aye is a primate that occupies the niche of a woodpecker. As luck (?) would have it, the aye-aye lives on Madagascar where there are no woodpeckers! (Mason, Georgia; "Grubs on Tap for the Ayeaye," New Scientist, p. 23, June 22, 1991.)
Reference. The aye-aye is a most peculia mammal. For more, see: BMA39 and BMT3 in our catalog: Biological Anomalies: Mammals I. Ordering details here.