76
THE ESSEX NATURALIST
there was very little eastward spread prior to 1945. This stable eastward
boundary has been noted by a number of authors (e.g. Shorten 1953,
Shorten 1954).
Some of the same reasons that account for the difficulty in establish-
ing a population of Grey Squirrels in Essex (i.e. the dual action of
competition with the native species and rigorous control measures)
also explain this early slow rate of spread. So effective were these early
control measures that Johnston (1938) seemed convinced that the
numbers of Grey Squirrels in Epping Forest were being held in check.
Fordham (1956) also believed that early invasions by Grey Squirrels
could be controlled by determined action.
However, control measures did not prove permanently effective, and
once the population of Grey Squirrels was well established, the east-
ward rate of spread was rapid, particularly during the period 1945 to
1955.
3. When Grey Squirrels colonised a new area of Essex, the pattern of
events was either for a rapid disappearance of the Red Squirrels,
usually within a year or two, or for a long period of coexistence. Thus,
in west Essex, the small woods and copses around Epping (e.g. Nazeing,
Little Parndon) were subject to a rapid disappearance of the native
animal, whereas in the main Forest Red and Grey Squirrels coexisted
for up to twenty-five years. Benham (1953) found that in Dorset the
average period of overlap between the two species was three years, and
that in most cases the Red Squirrel declined during the overlap period.
Benham also noted some cases of the Red Squirrel disappearing before
the arrival of the Grey—no similar events were noted in Essex.
The old story that the Grey Squirrel forcibly 'drove out' Red Squirrels
is not acceptable. To explain this replacement of Red Squirrels by
Greys one needs to look at the habitat preferences of the two species.
Shorten (1962) says that the Red Squirrel is 'subject to decline when it
can no longer find dense, secluded woodland. . . . Memories of red
squirrels living in small woods and semi-urban districts refer to the
period of abundance, when "overflow" animals did settle in such
habitats.' Not only is the size of the woodland important but also the
type of woodland. According to Tittensor (pers. comm.) Grey Squirrels
prefer broadleaved or mixed broadleaved/conifer woodland, which may
be in the form of scattered trees, small woods or large blocks, whereas
Red Squirrels prefer large stands of pure conifer. Both species can, and
do, live in alternative habitats but obviously when they are competing
and under stress each would be at an advantage, and therefore more
abundant, in its preferred habitat. In consequence Red Squirrels dis-
appeared rapidly from small pieces of broadleaved woodland (as oc-
curred in most of the small pieces of woodland in Essex), survived and
competed for longer periods of time in large tracts of broadleaved or
mixed woodland (e.g. Epping Forest, Donyland Woods near Col-
chester) and would probably only survive permanently in large tracts
of pure conifer (and since these do not exist in Essex one cannot expect
the Red Squirrel to persist in the county).
This question of habitat preference is not quite the complete answer