Are pine martens a panacea for Britain’s squirrel problems?

The invasive North American Eastern grey squirrel (Sciurus carolinensis) is the principal driver of decline in the native Eurasian red squirrel (Sciurus vulgaris) in Britain, primarily through disease-mediated competition and behavioural dominance, prompting interest in whether restoration of the European pine marten (Martes martes) could provide a nature-based form of biological control. Evidence from Ireland, Scotland and Wales indicates that pine martens can influence squirrel populations through both direct predation and indirect behavioural mechanisms consistent with a “landscape of fear”, with declining grey squirrel distributions and densities often coinciding with marten recovery and localised red squirrel expansion. This short review critically assesses whether these effects can be extrapolated to the fragmented and human-dominated landscapes of England and Wales. The ecological processes underpinning marten–squirrel interactions are examined, including predator functional responses, prey switching, behavioural modification of grey squirrels, and the influence of habitat structure, alternative prey availability and urban refugia. While pine martens demonstrably predate grey squirrels and may reduce their fitness and spatial dominance under certain ecological conditions, population dynamics and landscape constraints suggest that martens alone are unlikely to suppress grey squirrel populations at a scale sufficient to enable widespread red squirrel recovery in England and Wales. In particular, the slow reproductive rate of martens, the abundance of alternative prey, and the persistence of grey squirrel refugia in urban and suburban environments limit the potential for sustained biocontrol. We conclude that pine martens should not be regarded as a stand-alone solution, but rather as a potentially valuable component of an integrated management strategy incorporating targeted culling, fertility control, and habitat improvement. When applied strategically and at local scales, pine marten restoration may still contribute meaningfully to protecting red squirrel refugia and enhancing the effectiveness of broader conservation interventions.