SQUIRRELS IN ESSEX
75
1. Although the Grey Squirrels introduced around London spread rapidly
in every other direction there was virtually no eastward movement, and
Grey Squirrels did not colonise Essex permanently until 1935 (although
neighbouring Hertfordshire was colonised early in the century).
Animals that arrived prior to this date did not persist, although one
animal was recorded as far east as Colchester. (Middleton (1931b) noted
that isolated specimens or pairs frequently turn up suddenly as far as
twenty miles from any previously populated locality.)
Why these early invaders did not persist is uncertain. Throughout
the country the high population of Grey Squirrels present in the late
1920s fell dramatically in the autumn of 1930, this being due to a
combination of a failure of the beech mast crop, followed by an out-
break of coccidiosis (Middleton 1932). If any of these early arrivals did
persist until 1930 they did not survive these adverse conditions. Also
it seems that on the edge of the range, waves of invaders and scattered
individuals appear at fairly widely separated intervals prior to actual
colonisation—Fordham (1956) noted very similar events in north
Hertfordshire.
The effect of the Lea Valley in retarding this eastward movement into
Essex has already been discussed, and this geographical barrier was the
most important single factor in delaying the arrival of Grey Squirrels
in Essex. Shorten (1946) described unsuitable squirrel territory as
marshy and sparsely timbered, or industrialised, and the northern part
of the Lea Valley falls into the first of these categories, and the southern
part of the Valley into the second.
At one time a number of authors considered Essex and East Anglia
as comprising unsuitable habitat, and that this explained the difficulty
Grey Squirrels had in colonising Essex. Thus Fitter (1939) said 'much
of the country [in Essex outside Epping Forest] being unsuitable for it'.
Shorten (1946) likewise supported this view that the habitat was in
some way unsuitable, and Lloyd (1962) lent credence to her views with
the observation that four ten-kilometre squares in west Suffolk occupied
by Grey Squirrels in 1954 were unoccupied in 1959. Unfortunately the
way in which the habitat was thought to be unsuitable was never
explained, but this view is unlikely since once the Grey Squirrel had
secured a footing, the majority of Essex was colonised in only fifteen
years (from 1945 to 1960).
Another important factor to consider is that the Grey Squirrel
probably had difficulty securing a footing in Essex due to a thriving
Red Squirrel population. Over most of the country outside Essex the
Grey Squirrel moved into a vacuum left as a result of the decline of the
Red Squirrel population, which was thought to have been decimated by
coccidiosis. However, in west Essex there was always a thriving Red
Squirrel population due to the introduction of 1910. When Grey
Squirrels first appeared in Essex in Epping Forest they were ruthlessly
destroyed (Johnston 1938), and this, coupled with competition with the
Red Squirrels, almost certainly accounted for the early slow rate of
spread.
2. Although Grey Squirrels became established in Epping Forest in 1935,