The return of pine martens to Ireland and England has had surprising conservation benefits for native red squirrels through predation of invasive gray squirrels.
Gray squirrels killed in control programs suffer through shooting, drowning, and trapping. While control is practiced to protect native red squirrels, the welfare cost of killing millions of gray squirrels is significant. Gray squirrels are not native to Britain and Ireland but are not morally culpable for their introduction - they are experiencing lethal control for human errors. Natural predation by pine martens selects for squirrel behavior and ultimately involves predation stress and death, but this is natural ecological process rather than targeted control at scale. Conservation approaches that work with natural predator-prey dynamics may achieve conservation goals with lower total welfare cost than human-led culling programs.