It is unlikely that predators that are as rare as pine martens will affect the overall numbers of their prey. furthermore, pine martens have a varied diet. So their impact may be spread across many species of animal and bird and so is not likely to impact greatly on any one. It is also probable that pine martens are more likely to come across commoner species.
One of the largest investigations of pine marten diet was conducted in an area where 1,000-2,000 pheasants were released annually. Pine martens who lived in this area occurred at the highest recorded density. Despite this, pheasants formed only 4.5% of pine marten diet.
.It is reported that pine martens will only kill to eat, unlike the fox who has a reputation of killing sprees in hen-houses. It has also been reported by a farmer that pine martens were observed to enter a hen house, only to push the hens off their nests in order to steal their eggs.
Pine martens are often thought to be vicious killers of small livestock and pets in gardens. The victims' destruction could well be the work of foxes, dogs or birds of prey. Prejudice prevails over evidence, sadly.