When did red and grey squirrels start competition?

Red and grey squirrels began to compete significantly after the introduction of grey squirrels to the UK in the late 19th century, around the 1870s. The invasive grey squirrel outcompeted the native red squirrel for food and habitat, leading to a decline in red squirrel populations. This competition has continued, contributing to the red squirrel's status as a threatened species in many areas.