Factors affecting the distribution and population density of pine martens (Martes martes L.) in Scotland
The diet, habitat use and social organization of pine martens in Scotland was investigated by comparing data from marten populations at high and low density. Correction factors, determined from feeding trials with captive martens, were used to convert frequency of occurrence data, to estimates of the relative weight intake for each prey item in the scat. Spatial orientation and habitat utilization were determined from the radio tracking of 24 martens, 12 from each study area. In total 36 animals were caught, many of which were recaptured on a regular basis. All animals were aged by cross-sectioning of an extracted incisor and sexual activity in males was determined by measurements of blood hormones and abdominal scent gland activity. The density of martens in each area was assessed using an injection of radio isotope to label the scats of captured animals. The results showed that in both study areas the principal prey of martens were cervid carrion and field voles Microtus agrestis and that the preferred prey was field vole. The new method of interpreting the diet from prey remains in the scats suggests that the importance of invertebrates and fruit may have been over estimated by previous authors. A new method to analyse differential use of vegetation types form low resolution radio-fixes (fixes being assigned to grid cells likely to contain more than one vegetation type) is proposed. The results showed that martens selected vegetation types based on the cover each provided and that territories were established relative to a constant amount of woodland per individual: 126 + /- 40 Ha. Despite the high density of the preferred prey Microtus in open vegetation types, open vegetation was avoided within territories as well as in territory selection. It is suggested that selection for vegetation types, at this level, is driven by predator avoidance but that selection between different wooded vegetation types is determined by prey availability and to a lesser extent suitable den sites.