The European pine marten, Martes martes, is a member of the family Mustelidae within the order Carnivora. It is widespread throughout much of north and western Europe but rare or absent in much of its historic southern European range. The pine marten is omnivorous and feeds upon a wide variety of food including small mammals, birds, reptiles and amphibians, invertebrates, fruit, nuts and carrion in various proportions throughout the seasons, however diet is usually dominated by just two or three food categories, depending on seasonal and regional food availability. The pine marten is closely associated with forests and has traditionally been considered a forest specialist, however despite their close association with trees, they are not strictly forest-dependent and have adapted to a variety of landscapes throughout their range, not least in Ireland and Britain where deforestation in the 19th century led to <5 % forest cover.
In 2014, after years of anecdotal reports from foresters and gamekeepers, the first evidence that the recovery of the pine marten in the Irish midlands was linked to a significant decline in grey squirrel numbers was published (http://link.springer.com/article/10.1007/s10531-014-0632-7). The study also confirmed that the once beleaguered red squirrel population was able to recolonize its former range, including large broadleaved woodlands, which had been dominated by grey squirrels for more than 30 years. The study found that where pine martens had returned to healthy numbers, grey squirrels had all but disappeared (from an area of about 9000km2). But in areas where pine martens were absent, or present only in low numbers, grey squirrels persisted at “invasive” levels. Furthermore, the areas which red squirrels had recolonized naturally were exclusively those with healthy pine marten populations.
The study also found that the occurrence of grey squirrels in the diet was much higher than that of the red squirrel, confirming that grey squirrels are more likely to be preyed upon by martens in the rare event that their ranges overlap. However, it is not yet known whether direct predation by pine martens is the cause of the negative correlation between the distributions of pine martens and grey squirrels. Other possible effects of having a healthy native predator around include behavioural impacts such as predator avoidance and changes in foraging behaviour that lead to reduced fitness, or physiological effects such as a stress induced reduction in reproductive success or increased susceptibility to disease or infection.
Pine martens (Martes martes) are the second rarest mammal in Britain, and although they are recovering well in Scotland and Ireland (a result of increased habitat availability and legal protection), they remain practically extinct in England and Wales; a result of habitat loss, and historic persecution. The Vincent Wildlife Trust is currently undertaking a population reinforcement project in Wales.
Ongoing research at the University of Aberdeen aims to determine whether the recovering pine marten population is playing a role in Scottish squirrel population dynamics, with the ultimate aim of determining the potential for the pine marten’s recovery to aid the survival of the British red squirrel population. The results of the study will be published in 2017.
Dr Emma Sheehy
ELEVATE Research Fellow
School of Biological Sciences
University of Aberdeen
School of Chemical and Life Sciences
Waterford Institute of Technology