The recovery of grey squirrel (Sciurus carolinensis) populations after intensive control programmes

Grey squirrel, Sciurus carolinensis, populations have been subjected to various degrees of control in the woodlands of Ireland and Britain since their introduction. The populations readily recover, but the recolonisation rates and other ecological effects of the culls have not been fully examined. Monthly live trapping programmes were used to monitor the grey squirrel populations in two woodlands. Culls, where as many grey squirrels as possible were removed by trapping, were conducted on five occasions; three in one woodland and two in the other. The squirrel populations recovered within ten weeks in four of the five culls. Post-cull populations tended to consist of unmarked adult squirrels that had entered from outside the woodland. One cull attempted in the autumn was not a success, as capture rates were low and the population had returned to its pre-cull levels within three weeks. Many young squirrels entered the population following this cull. Some long-term repercussions of the culls were evident, even after the population density had recovered. The age profile changed, with the removal of breeding females reducing the numbers of young squirrels for the following year. Breeding levels were also reduced as the recolonising populations were slow to start breeding. Home ranges of surviving squirrels expanded if the population density remained at a reduced level, and core areas often shifted following a cull.