184 THE ESSEX NATURALIST
The records of adders in the area during 1967 (Table 1) show
that in the early spring most of those seen were in zone 1. In late
spring and early summer they apparently migrate to zone 3, for,
during late April and May most of those seen were in this area,
with a few in zone 5. In these zones they will be found on the
edges of hawthorn clumps, bramble bushes and tussocks of grass,
sheltered from such wind as might be blowing. Observations in
1967 were minimal in July and August, due to adverse weather
conditions, but by September, when adders were next seen, they
were present both in zone 1 and zone 3, and by October were seen
only in zone 1.
The distribution of snakes in the area on four separate dates in
April, May and October is shown in Figure 3 and illustrates clearly
the different areas they are found in during one season.
Our interpretation of these migrations is as follows, and it is
gratifying that it confirms a theory that we have long held as to
seasonal movements. The dry, well drained woodland, with its
plentiful leaf litter and adequate shelter (zone 1) is clearly chosen
to hibernate in, for the snakes are found there only in early spring
and late autumn. With the coming of summer and the increase in
shade from the leaves of the canopy and shrub layers, the snakes
move into the grassland, where they mate and spend the summer
before the females give birth to the young. In autumn, the adults,
if not the young of the year, return to the wood to hibernate.
Reference to Table 1 shows that in spring and autumn more
male adders are recorded than females. During the summer