190 THE ESSEX NATURALIST
Herpetological Notes
1. Conservation of a Population of Common Frogs
During the past seven years, I have been trying, with the help
of several friends, to protect a population of frogs which
habitually spawn in a marsh in the Woodford area.
Spawning in the marsh usually takes place ten to fourteen
days earlier than in other ponds in the Epping Forest area, earlier
even than in a pond only two hundred yards away. This is
possibly mainly due to the open aspect of the pond, and the
fact that it is shallow. This shallowness and the early spawning
habit both militate against the survival of the population, for the
spawn is laid when the marsh is filled with winter rain, which
evaporates long before the tadpoles would have time to
metamorphose into frogs.
The spawn clumps are collected in nets and removed in
buckets to a neighbouring pond, where they are distributed in
such a way as to be out of reach of children and other collectors.
The clumps of spawn removed have been counted each year
and the figures obtained (see table) lead us to believe that due to
our efforts a substantial increase in the population has been
achieved.
The year 1967 differed from the five previous years, principally
in that there were four spawning sites instead of the usual one.
Even early on, however, it was apparent that it was going to be
an exceptional year. On the first day of sighting frogs in the
marsh (March 4), 17-20 were seen at the usual site. On March 6
we counted 50 frogs distributed in three sites about twelve feet
(3.6 in.) apart. Two days later we counted 60 frogs and activity
was intense among the males, and croaking was heard. We
discovered the fourth site, which was larger than the others, on
March 12. Considering that a positive count of 60 frogs had
been made before the discovery of this fourth, and largest, site,
and that these were mostly males from their behaviour, it seems
likely that the total population in the marsh is around 200.
In 1968 we were disturbed to find the marsh heavily polluted
with oil and other matter, and the water level considerably lower,
mainly due to a dry winter and the clearing of a nearby drainage
ditch. Nevertheless the frogs still returned and some 40 clumps
of spawn were removed. A spawning site which contained a
considerable amount of spawn was also discovered in a nearby
pond. It would appear that some of the frogs from the marsh
have migrated to this pond to spawn.
This is in agreement with observations of the frog in Epping
Forest in general. Ten years ago it was considered to be rare
in the area but, from the increase in records of frogs seen, or