BROAD FEATURES OF ORNITHOLOGY OF ESSEX. 263
these birds nested has resulted in their disappearance. Prior
to the construction of the reservoirs there was no fresh water
in the county capable of sheltering such gatherings of birds
as may now be seen. Moreover this land, which is used for
water-storage, would have been densely covered with buildings.
The features, which make most impression on the eye, are
colonies and particularly those of larger birds. The Rook is
probably our greatest colonist and there are many rookeries of
varying sizes scattered over Essex. I regret, however, that we
have not much information regarding our rookeries. In some
counties a census of Rooks' nests has been taken so that not
only are the position and size of the rookeries known, but also
a knowledge of the total number of pairs nesting is gained. It
may be that some day by a united effort we may be able to
repair this omission. We have also little information regarding
the roosts of the Rook. One is stated to have existed at Gosfield
Park. It had been occupied for centuries and was said to
have been used by as many as twenty thousand birds, but it was
deserted in 1926. Apart from the rookeries most of the colonies,
certainly of the larger birds, are situated near the coast and
they include heronries, gulleries and ferneries. Heronries back
to mediaeval times were of interest on account of their value
to the falconer, yet it is difficult to trace the history of those 
which are in occupation today. Assuming that none has been
deserted recently Essex has twelve heronries, two having been
discovered since I last wrote on this species. Most of them
are within easy flight of the coast and with the exception of two,
those in the Lea Valley and Wanstead Park, all are in the
eastern half of the county. In so far as is known the colony at
Wanstead Park is the oldest. The earliest date at which we
find it mentioned is 1834, when it was said to be long established
and very populous. I regret to say that it has declined seriously
in recent years. In 1915 there were 74 nests, the highest number
in the history of the colony, but in 1938 there were only fourteen,
this being the lowest number ever recorded. This decrease
has been compensated by the increase of the heronry at the Lea
Valley Reservoirs, where there were five nests in 1928 and fifty-
six in 1938. This is one of the more recent colonies, it having
started about 1914. In certain respects this heronry is
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