1. Department of Environmental Conservation, University of Massachusetts Amherst, Amherst, Massachusetts 01003 USA
2. Natural Heritage and Endangered Species Program, Massachusetts Division of Fisheries and Wildlife, 1 Rabbit Hill Road, Westborough, Massachusetts 01581 USA
3. Wheaton College, Norton, Massachusetts 02766 USA
4. Mass Audubon Wellfleet Bay Wildlife Sanctuary, Wellfleet, Massachusetts 02663 USA
5. Centre for Research into Ecological and Environmental Modelling, School of Mathematics and Statistics, University of St Andrews, St Andrews, Scotland, United Kingdom KY16 9AJ