200 THE ESSEX NATURALIST.
Although none was seen in 1923, there can be no doubt that
this bird was the herald of the remarkable change of the status
of the species. In 1924 it was observed on many occasions, the
largest party containing two adult males and ten brown-headed
birds, and it has appeared annually in subsequent years to
the winter of 1933-4. The largest party recorded contained
six adult males and nineteen others, and was seen on
February 24th, 1934. The extreme dates of its sojourn are
December 2nd, 1933, and April 14th, 1929.
The Cormorant, Phalacrocorax carbo carbo (L.).
It. is an occasional visitor in very limited numbers. It-
has been recorded in 1921, and from 1924 to 1932 inclusive,
excepting 1927 and 1930. The birds have been seen in all
months of the year except July. One or two have usually been
seen. On February 13th, 1926, one, which had developed the
white thigh patches of the breeding season, was seen.
Occasionally birds make a prolonged stay of from two to three
months.
The Shag, Phalacrocorax aristotelis aristotelis (L.).
It has been recorded on one occasion only, the present writer
having seen one on the West Warwick on December 25th, 1926.
The Great Crested Grebe, Podiceps cristatus cristatus (L.).
It is, as a species, a numerous resident. It was established
as a breeder in 1904, and from 20 to 24 pairs have bred annually
for some years. Nesting operations are confined to the smaller
reservoirs with islands and suitable banks. It was estimated
that in June, 1931, there were 30 non-breeders present. The
Grebes may be seen in every month of the year. The numbers
are at their highest during the autumn migration, from July
to September, when as many as 150 have been counted. Then
the numbers steadily decrease until they are at their lowest,
when there may be less than twenty. The numbers commence
to increase again from the beginning of the year, at which time
the breeding birds, which have emigrated, reappear. The
migrations are, however, difficult to interpret and vary from
year to year. Weather conditions are an important factor.
The Slavonian Grebe, Podiceps auritus (L.).
A rare visitor which has been recorded on three occasions:
two, March 19th, 1927; one, October 30th, 1931; and one,
September 24th, 1932.