Scanner Helps Track Zebras’ Bar Code

Caren B. Les, caren.les@photonics.com

Zebras – those living, breathing bar codes – can now be scanned by a method that could help scientists track individual animals in the herd and add more black-and-white facts to our knowledge of the animal kingdom.

The StripeSpotter automatic identification system for individual animals with prominent stripes or patches was developed collaboratively by scientists at Princeton University in New Jersey and at the University of Illinois at Chicago. Two species of zebra in Kenya, Africa, were the (sometimes unwilling) participants in the study.

While doing field research, the scientists captured digital images of the zebras in the wild, then cropped the images to a region of interest – an area of the animal’s anatomy that appeared consistent across a number of pictures. Using their own StripeCodes algorithm and “noisy” photographs taken in the wild, they built a biometric database of individual animals, differentiated by their coat markings. The “noisy” aspects of the photos included uncooperative subjects, coat deformities, and variations in image exposure, scale and perspective.

The investigators compared the coat markings in a new image of an unknown animal against the database to determine whether the animal had been previously observed and identified with the system. The algorithm extracted simple image features and used a dynamic programming algorithm to compare images.

A database of digital zebra images and an algorithmic approach help scientists track individual zebras in the wild. The images are cropped to the same region of interest in the animal’s anatomy. The image of an unidentified animal’s coat markings are compared against those in the database to determine if the animal has been previously sighted. Photos courtesy of Mayank Lahiri.

Identifying individual wild animals as they are sighted going about their daily lives has been a challenge. Embedding an electronic tracking device in a wild animal can be risky business, not to mention expensive. Other options, such as manually recording data on animals from photographs or video, obtaining genetic markings from excrement, or capture-and-recapture techniques, have been problematic in terms of cost, efficiency or accuracy.

As for these “markedly” exotic creatures, hopefully the saying is true – a leopard cannot change its spots, nor a zebra its stripes – as we set out to identify them by those markings.