1. Centre for Resource and Environmental Studies, The Australian National University, Canberra, A.C.T. 0200, Australia
2. Department of Conservation Biology, Daniel F. and Ada L. Rice Center, Brookfield Zoo, Brookfield, Illinois 60513, U.S.A.
3. Division of Biochemistry and Molecular Biology, The Australian National University, Canberra, A.C.T. 0200, Australia