Movements of the Grey Squirrel as Revealed by Trapping

Abstract

The grey squirrel, Sciurus carolinensis Gmelin, is valued as a game animal in many parts of its native habitat in North America and is the subject of intensive research on conservation and management. In Britain, it is regarded as a pest because of its destructive habit of stripping bark from living trees (notably beech, Fagus sylvatica L. and sycamore, Acer pseudoplatanus L.). Research in Britain consequently has been mainly concerned with squirrel control, particularly by means of trapping. In 1954 we began an investigation into the seasonal success of trapping as measured by the proportion of a known population that could be captured in baited live-capture traps, captured animals being marked and released. A regular feature was the capture of more unmarked adults in June than at any other time and it was obvious that movements of squirrels between the study area and outlying woodlands were affecting the investigation and by 1956 it became apparent that more individuals were being handled than could be fully supported by the study area. The movements of marked squirels had not been studied in Britain up to this time and existing estimates of range were based upon sight records of small groups in parks, gardens or small woods. That grey squirrels were capable of making long journeys was apparent from sightings on the fringes of their geographical distribution when squirrels were sometimes seen many miles from their known range, and from re-invasions of isolated woods after clearance; but the nature of the movements, their frequency, and the conditions that promoted them were not known. Information about movements of grey squirrels in the United States was also sparse at this time and inapplicable to the broken woodland that comprised the study area. Our initial plan was therefore modified to include the study of movement. After an initial phase of concentrated mark and recapture work in a 16-ac wood, at Alice Holt in Hampshire, traps were set in all woodland within a 2-mile radius of this central area to provide as much information on movements as labour and materials would permit. The study was planned and begun by M.S. After 4 years, H.G.L. took charge for 12 months, handing over to K.D.T. for the final 18 months. The organization of the field work during the entire study was undertaken by F.A.C. Data were collected on several aspects of grey squirrel biology, other than movement, and information on reproduction and methods of determining the age of squirrels collected at the end of the study will be published elsewhere.