THE BIRDS OF THE LEA VALLEY RESERVOIRS. 189
but, as has already been stated, the Lea Valley is now
similarly affected. It will be of interest to watch the de-
velopment of this new impulse and to note if it has any
influence on other species. I have no doubt that the reason
for the differences between the bird-life of the two series
of reservoirs is that there is much more migration along the
Thames and it is not improbable that the nightly movement
of gulls to the King George may have originated from the
Thames movement. To debate this question here would take
too long and in any case I had already discussed the subject
at some length. The title of the resulting article will be found
in the bibliography.
A brief recapitulation may be useful at this stage. The
reservoirs, although they have added no new species to the
Essex list, have had a considerable influence on the avifauna
of the County. This influence has exerted itself not only on
that type of bird to which water is necessary but also on other
types of birds. The most remarkable features among the
passerine birds are the large numbers of Carrion Crows, the
breeding colonies of Reed Warblers and Yellow Wagtails and
the Rock Pipit as an inland species. A heronry has been
founded. But for these large sheets of water we should have
been without such great assemblages of ducks, and the Smew
and other species would have been unknown to us as winter
residents. The nesting of the Great Crested Grebe in such
numbers and the appearance of such large migratory flocks-
would have been impossible. We should have remained in
ignorance of the many species of waders and other types of
birds which traverse the inland parts of the County.
We have restricted ourselves to a consideration of the birds
in so far as they affect the reservoirs. I propose now to go
further afield and deal with points of interest in the histories
of some of the species. Rare as the Hooded Crow may be at
the reservoirs it is a common winter resident along the north
coast of Essex, but it does not nest in the County, although it
once did, so we must go some way to find its nest. In Scotland,
where it breeds freely, it not infrequently interbreeds with its
very close relative the Carrion Crow, where the breeding
ranges of the two species overlap. Trees are used for nesting
purposes, but the species may be common where there are no