BIRDS OF THE THAMES VALLEY. (ESSEX ONLY). 165
characteristic bird of the river, was seen on all visits, varying
very much in numbers. On occasion the species was present
in large gatherings, especially on Mucking Flats, as on July 18,
1926, and again on July 24, 1927, when, on account of the
abundance of the species, the river presented an animated
spectacle. On October 16, 1927, I estimated that about 2,000
gulls were present, almost entirely Black-headed. On August 22.,
1926, some still retained traces of the brown head and on August
21, 1927 none was seen with any brown remaining. A single
bird was seen in full breeding dress on 27/2/27 and by 13/3/27
most of the birds were in this condition. On 19/2/28 some had
partially adopted the brown hood.
Common Gull (Larus c. canus L.). Identified during all
months of visits, generally in small numbers, although occasion-
ally numerous. At no time did this species rival the numbers
of the Black-headed.
Herring Gull (Larus a. argentatus Pont.). Identified during
all months of visits except March, April, May and November,
always in limited numbers and at no time approaching the
numbers of the Common Gull.
Lesser Black-backed Gull (Larus fuscus L.). Mucking Flats,
several, 18/7/26, several, 28/8/26 ; Canvey Island, three or four,
12/9/26 ; Vange Creek, one, 24/10/26 ; Mucking Flats, a number,
24/7/27 ; three or four, 11/9/27, one, 2/10/27 ; Holehaven
Creek, two, 21/8/27 ; Shellhaven, one, 28/8/27. All these records
even including that of 24/10/26, may be said to be migrational,
and I certainly have no winter records.
Great Black-backed Gull (Larus marinus L). Identified
during all months of visits except February, March, May and
November, generally in very small numbers. The largest number
was seen on 12/9/26, when two flocks of five and thirteen were
seen. Two were seen as far up the river as Stone Ness, 30/1/27.
Iceland Gull (Larus glaucoides Meyer). On 13/11/27 I noticed
a single gull on Pitseahall Fleet, among the many Coots. As
the bird was some distance up the fleet from me, I put up my
telescope and was surprised to find that the feathering of the
head was curiously dark. At a distance, had the bird not been
too large, it might have been a Black-headed Gull. I knew that
this was a new species to me, but the identification baffled me.
Proceeding up the fleet I disturbed the gull, which flew over