168
THE ESSEX NATURALIST.
observed. Although, no doubt, this Plover has been recorded
from all round the coast, yet these observations prove that the
species is much scarcer on the Thames and Crouch than on the
other estuaries. The Knot is another species which is in the same
position as the preceding, not having been identified south of
the Blackwater. The influence of the shingle is manifest for it
accounts for the occurrence of the Sanderling, Oystercatcher and
Turnstone, all three not having been noted on the southern part
of the coast. The consideration of the waders may be con-
cluded by adding that practically all this group was more
numerously represented in the north than in the south. If the
Thames alone had to be considered it might be feasible to think
that the difference was due to the commercial activity but, as
the Crouch is quite free from such influences, this is untenable.
The cases of the Brent Goose and the Red-breasted Merganser,
are further instances of species which were identified with some
frequency in the north but not at all in the south. Evidence of
further differences will be found in the systematic lists.
The working out of the distribution of the Carrion and Hooded
Crows has been of much interest. Whilst the former is commoner
in the south becoming less so in the north, the reverse must be
written of the Hooded Crow which is practically non-existent
along the Thames, although not uncommon between the Colne
and the Stour, and what is most remarkable, also on the Kent
side of the estuary.
The question of migration is treated freely, not merely to deal
with actual passage through the county, but also with arrivals
and departures, increases and decreases. The evidence of my
observations suggests that Essex is not so much affected by
migrating birds as neighbouring counties, as, for example,
Norfolk. In each of my seven years of observation there has
been ample evidence of migration, chiefly of limicoline birds and
gulls. This movement was observed from the end of July into
the earlier part of August, and included such birds as Whimbrel,
Green and Common Sandpipers, Greenshank, Sanderling, Lesser
Black-backed Gull, etc. A movement, probably annual, of
Terns up the Thames was noted at the end of August in 1926
and 1927. These complete the passage-movements observed.
The Great-crested Grebe, with one exception, was only
recorded on dates which might be described as coming within