Source: This article was adapted from Sign and The Art of Tracking—A Guide to Support Law Enforcement Tracking and Anti-Poaching Operations, by Christian Nellemann, UNEP/GRID, Arendal, Norway, Rapid Response; with Jack Kearney, U.S. Border Patrol, retired; Stig NĂ¥rstad, Norwegian Police; and the INTERPOL Environmental Crime Programme. Copyright © 2011 by Interpol, Lyon, France; and UNEP/GRID, Arendal, Norway. Excerpted with Expressed Written Permission. All Rights Reserved.