Scanning the savanna with a pair of binoculars and a global positioning unit, biologist Robin Reid counts the number of zebra, giraffe and cows that graze in one of the world's most famous wildlife reserves. Reid is the lead scientist in Mara Count 2002, one of the most ambitious attempts ever to inventory an ecosystem. Nineteen teams and two planes counted 23 species and classified the vegetation in an equally divided 965 square mile area.