Passage II

Zebra ID: Biological Bar Codes

[1]

Even though every zebra has a unique pattern of bold stripes on its coat, the animals look remarkably alike. Zebras are willful animals. When in a herd, they become a mass of blended stripes and similar features that confuses a lion on the hunt. One zebra resembling another is not beneficial to researchers, though. Biologists trying to monitor individual zebras sometimes joke that finding one in the wild typically is easy it’s finding the same one twice that’s hard.

[2]

Working together, scientists at the University of Illinois and Princeton University developed a software program called StripeSpotter, which catalogs and identifies zebras. StripeSpotter translates the pattern of stripes on a zebra’s side, into an identifier, similar to a bar code, that can be compared to other zebra stripe-pattern identifiers that have been stored in a database.(20)

[3]

The process begins when a researcher uploads a still photograph of a zebra to StripeSpotter. [A] The researcher then crops a rectangular section of the photograph, making sure to capture the stripes on the zebra’s side. [B] StripeSpotter converts that section into a stark black-and-white image composed of parallel, vertical lines. The widths of the lines correspond perfectly to the widths of the zebra’s stripes. Providing the zebra’s “StripeCode,” unique to each animal in much the same way a fingerprint is unique to each person. The StripeCode is logged in the database, where a researcher uploading a new photograph of a zebra can scan the stored codes to find a potential match.

[4]

[C] StripeSpotter has proved so useful that it’s developers plan to design similar programs for identifying other animals. Any pattern present over an animal’s life could be translated into an identification code—spots on a leopard’s hide, the wrinkled trunk of an elephant, rings on a tortoise’s shell. So far, StripeSpotter has helped researchers thoroughly monitor the social interactions and migration patterns of endangered zebra species in Kenya. [D]