Biomimetic investigation of the impact of the ear canal on the acoustic field sensitivity of aye-ayes

Abstract

The aye-ayes (Daubentonia madagascariensis) are an extremely rare lemur species and the world’s largest nocturnal primate. Tapping on tree bark with its unique elongated middle finger, the aye-aye listens closely for signs of cavities or insect larvae inside; this is a unique acoustic-based foraging behavior called “percussive foraging” or “tap-scanning.” Tap-scanning requires the animal auditory system to exhibit exceptional acoustic receptive field sensitivity. This study provides an insight into how the ear canal of aye-ayes might have an impact on their acoustic field sensitivity; this was achieved using a biomimetic approach to simulate the tapping mechanism. To this end, the aye-aye’s pinna and ear canal were 3D printed. The pinna in the cupped position was preserved, and the acoustic field was evaluated in the time and frequency domains. The results suggest that the pinna with the ear canal can substantially enhance the receptive field sensitivity of the aye-aye’s auditory system by shaping a focal area at the tapping location. Furthermore, changes in the sound field receiving beam pattern for higher frequencies resulted in an increase in the receiver dominant frequency, indicating the evolution of the aye-ayes’ external ear to create a physical filter for excluding unnecessary low frequencies in the focal area.