Turning birds into bats : Multi-modal tracking to study collective behaviour

Abstract

Acoustic localization has been used to track numerous vocalizing animals, including whales, bats birds by measuring the time of arrival differences of a sound recorded by multiple receivers. This method, however, requires the species of interest to vocalize regularly to achieve decent temporal resolution. In order to track the movements of birds that do not vocalize regularly, a miniature, radio controlled ultrasonic speaker is attached to the birds and constantly emits ultrasound chirps. The chirps from various tagged animals can be discriminated based on information encoded in the signal. A 30 microphone array covering the ceiling of a large aviary (14.8 × 6.6 × 3.9 m) is used to record the chirps and provides the basis for accurate localization of the sources. As the chirps do not overlap with the frequency of the animals vocalizations, these can be localized and assigned individually in a flock of moving birds. In addition, a VICON motion capture system provides a simple and accurate method to ground truth the acoustic localizations as it records very precise movement information of the individuals while line of sight is between the marker on the animal and a number of cameras is established. The acoustic and visual tracking systems working together provides a unique and novel answer to consistent and precise localizations of non-vocalizing individuals (and groups of individuals) as they move through space.