1. Resource Ecology Group; Department of Environmental Sciences, Wageningen University; Bornsesteeg 69 NL-6708 PD Wageningen The Netherlands
2. Forest Authority Research Division; Alice Holt Lodge, Wrecclesham Farnham Surrey GU10 4LH
3. Lasswade Veterinary Laboratory; Bush Estate Penicuik Midlothian EH26 0SA