The relationship between grey squirrels (Sciurus carolinensis) and native red squirrels (Sciurus vulgaris) is of public interest, especially regarding the decline of red squirrel populations where grey squirrels have been introduced. While both species coexist in some regions, grey squirrel presence often leads to a rapid reduction in red squirrel numbers. This prompts questions about their interactions and the causes of this population shift.
Direct Confrontations
The idea that grey squirrels directly kill red squirrels is a common misconception. Interactions typically involve aggressive displacements, where larger grey squirrels outcompete red squirrels for resources and territory. While generally not lethal, these confrontations can inflict injuries and cause significant stress. These are primarily territorial disputes and competition for food, rather than predatory behavior.
Ecological Disadvantages for Red Squirrels
The decline of red squirrel populations in the presence of grey squirrels stems from ecological disadvantages. Grey squirrels possess traits that give them a competitive edge, impacting red squirrel survival.
Grey squirrels are more efficient foragers, outcompeting red squirrels for food. Their larger size and ability to digest unripe acorns and other seeds, less accessible to red squirrels, provide a significant dietary advantage. This pressure is pronounced during food scarcity, impacting red squirrel survival and breeding. Grey squirrels also thrive in a broader range of habitats and food sources, including broadleaved tree bark, expanding their competitive reach.
Habitat displacement also contributes to the red squirrel’s decline. Grey squirrels adapt well to broadleaf woodlands, common in many landscapes, while red squirrels prefer coniferous forests. Though red squirrels can inhabit broadleaf areas, grey squirrels thrive in these mixed habitats, displacing them. This pushes red squirrels into fragmented or less ideal coniferous areas, limiting resources and increasing vulnerability.
A significant factor in the red squirrel’s decline is squirrel poxvirus (SQPV). Grey squirrels often carry this virus asymptomatically, but it is typically fatal to red squirrels. The virus causes severe skin lesions, ulcers, and scabs, especially around the eyes, mouth, and feet, leading to lethargy, blindness, and death within about 15 days. Transmission occurs through direct contact with infected lesions or contaminated surfaces like feeders. This disease alone can cause red squirrel populations to decline 20 to 25 times faster than competition for food and habitat.
Protecting Red Squirrels
Conservation efforts safeguard red squirrel populations from these threats. A multi-faceted approach addresses both habitat and population management.
Habitat management is a key strategy, focusing on creating and maintaining suitable coniferous forest environments where red squirrels thrive and grey squirrels are less likely to establish large populations. This includes ensuring a continuous canopy for movement and diverse conifer species for consistent food. Managing woodlands to be less attractive to grey squirrels, by limiting broadleaf trees, also forms part of this approach.
Controlling grey squirrel populations is another aspect, especially in red squirrel strongholds. This involves targeted programs like trapping and shooting, considered most effective for preventing competition and disease transmission. Public involvement is encouraged, with individuals reporting squirrel sightings and supporting conservation organizations. These combined efforts aim to provide red squirrels the best chance of survival and recovery.