Brehms Tierleben, Band 1: Die Säugetiere I

Specialized use of two fingers in free-ranging aye-ayes (2008)

The aye-aye’s strangest finger isn’t its only tool.

A study of four of these lemurs found the thin third finger suited precise probing, and the stronger fourth suited scooping and deeper access. Their uses overlapped.

The aye-aye has two different finger tools

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An illustrated aye-aye perches on a branch in a night forest. Large ears, amber eyes, coarse dark fur and a bushy tail frame a hand with a thin middle finger beside a longer, sturdier fourth finger.

The animal behind the hand

A new explanatory view of one aye-aye hand distinguishes the very thin third finger from the longer, sturdier fourth finger. Small labels 3 and 4 point to the correct adjacent digits. Labels: 3, 4.

Two adjacent tools

An illustrative aye-aye feeds through a small opening in jackfruit skin. Its longer, stronger fourth finger reaches into the fruit while the slender third finger remains visibly separate.

The aye-aye has two different finger tools

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