Pine martens are agile, opportunistic predators whose prey selection affects the welfare of multiple prey species while the marten's own welfare depends on prey availability.
Pine marten welfare and prey selection involves a complex interplay between the marten's own welfare needs and the welfare of the species they predate. Individual marten welfare is determined by prey availability across all seasons: in spring and summer, small mammals and bird eggs provide protein; in autumn, berries, fungi, and invertebrates supplement diet; in winter, cached food and opportunistic hunting provide nutrition. Marten welfare deteriorates in periods of prey scarcity, when animals may lose body condition and show increased ranging behaviour in search of food. The documented suppression of grey squirrel populations in areas where pine martens have recovered - with grey squirrels spending more time on the ground avoiding marten predation and suffering higher mortality - creates welfare harm for individual grey squirrels while providing conservation benefit for red squirrels through reduced competition and disease transmission. This multi-species welfare interaction - where one predator's welfare and natural behaviour simultaneously harms one prey species and benefits another through trophic cascade effects - illustrates the complexity of applying welfare frameworks to natural ecological systems.