CENSUS OF ESSEX ROOKERIES. 1966 175
Density
The 1966 Census yielded a total of 6,376 nests in 385 rookeries.
Taking the area of Essex as 1,528 square miles this gives a mean
density of 4.1 nests or 8.2 breeding birds per square mile. The
average size of a rookery 16.5 nests.
Regional Distribution
The rookeries were marked on a map of Essex (Fig. 1). This
shows that the Rook nests mainly in West-central Essex. There
are greater concentrations in the North than in the South, and
in the West than East. Rooks tend to concentrate in the upper
valleys of the rivers. The maximum altitude being between
160-250 feet (49-76 m) above sea level. The bird is thinly
represented along the coastal strip, except for a few local
rookeries, e.g. near Clacton. The chalk of the North-west and
the borders with Cambridge appear to be avoided, as is the
Thames Valley.
The map indicates that there are concentrations of high
density to be found spread across the upper valleys of the Roding,
Chelmer and Pant rivers. It is in these areas that the majority
of nests are to be found. It is also noteworthy that it is here
that rookeries of above 50 nests and up to and over 100 nests
occur.
The population along the Colne Valley is small, and along the
Roach there are a few isolated rookeries. The Thames Valley is
devoid of any recorded rookeries.
Some rookeries are to be found close to human habitation,
this is particularly so in Saffron Walden, and was the case at one
time in parts of Brentwood. Some towns which would be
expected to support rookeries, however, have very few.
Distribution by Trees
Rookeries were found in thirteen species of trees, the trees
recorded were as follows: —
Elm 241 nests Beech 13 nests
Oak 73 Willow 6
Ash 54 Plane 3
Horse Chestnut 27 Hornbeam 1
Sycamore 18 Conifers 30
Lime 14 (Larch, Pine)
It would appear that in Essex Rooks prefer Elm over any
other species, and also that there is a preference for deciduous
trees. Evergreens are, however, used as is the case along the A.12
road opposite Hylands Park near Chelmsford.
Large Rookeries
Large rookeries of over 100 nests are to be found at the
following places:—Salcot (Map Ref. 945145) 150; Chignal Smealy
(Map Ref.) 664116) 149; Great Bardfield (Map. Ref. 702277) 117;