A SURVEY OF ADDERS IN AN AREA OF EPPING FOREST 181
were available at different times. This meant that the area could
not be searched with equal thoroughness on each visit. The area
was, however, visited on twenty-six occasions between February
28th and October 23rd. The area was quartered by the observers
as thoroughly as their numbers and the vegetation would allow.
Despite careful searching, it is often very difficult to find adders,
particularly when the shrub layer is in leaf and dense. Penetrating
a tangle of scrub oak and bramble unobserved, to scan each small
clearing for adders lying in a patch of sunlight on a carpet of dead
leaves, can be both painful and unrewarding, but the sheer area of
the grassland, where every bush and tussock has to be carefully
investigated, reduces the search to that of finding the proverbial
needle in a haystack. Immature adders are extremely difficult to
see as they curl up to approximately the size of a penny.
The weather also affects the number of snakes seen. In 1967,
from June to September the weather became progressively warmer
and, as the temperature increased, the adder count fell. On seven
visits in July and August no adders were observed (see Table). In
September the weather at weekends was cold and wet, and again
no snakes were seen; and not until mid-October was there a week-
end with favourable weather conditions, when adders were again
counted.
The record of adders seen is essentially a count of those that
are lying visible on the surface; others, presumably, are lying
hidden under leaves or grass. Obviously, it is also a count of un-
disturbed adders, those which the observer found before the snake
disappeared into hiding. Bearing these factors, and the limited
numbers of observers and time available, in mind, it is likely that
only one in every three adders present is recorded at any one visit.
This proportion, which is a subjective estimate, is partly confirmed
by the number of occasions on which some particularly distinctive
and recognisable adder, known to usually inhabit a restricted
habitat, is not found, despite the tendency for observers to persist
in searching for a "known" and familiar adder.
A more accurate estimate of population would be obtained by
marking all adders caught and checking their identity on subse-
quent visits. However, a programme of this nature would require
far more time than we have available, and more important, the
repeated capture and handling of the adders could habituate them
to close human contacts—a feature we would consider undesirable
in an area to which the public have unlimited access.
The area studied lies on a slope facing south-south west (Fig.
2); the foot of the slope drains to a stream which lies on the 200 ft
(60 m) contour, while the highest part of the area lies close to 300
ft (91 m), O.D. and is estimated to lie at about 280 ft (85 m). The
area overall measures approximately 300 yds (275 m) in an east-
west axis, and 200 yds (182 m) on the north-south. On the whole
it is well drained, but the base of the slope becomes rather damp
in wet seasons,