Sadlier LMJ, Webbon CC, Baker PJ, Harris S. Methods of monitoring red foxes Vulpes vulpes and badgers Meles meles: are field signs the answer? Mammal Review. Volume 34, Issue 1-2, pages 75–98, January 2004
http://onlinelibrary.wiley.com/doi/10.1046/j.0305-1838.2003.00029.x/full

hunting index of population density (HIPD)
see: http://www.sekj.org/PDF/anzf32/anz32-093-097.pdf