ESSEX BIRD-MIGRATION. 143
breeding area. The recovery of the Black-headed Gull, which
was born at Lake Zurich in Switzerland, supports this, as Lake
Zurich is much to the south of Britain. The information
derived from the ringing of Black-headed and Common Gulls is
sufficient to justify the formation of conclusions. It would
appear that practically all our winter population of these two
species is composed of foreign birds as, apart from a Black-
headed Gull, ringed in Cumberland, all the birds recovered had
been ringed abroad. We have yet to ascertain what happens to
our native Black-headed Gulls.
In this account I have drawn attention to the main features
of Essex bird-migration. The systematic list which follows
supplies further details, and what is not there included will be
found in "A History of the Birds of Essex."
I terminate this consideration of the subject, with an appeal
for much more work, particularly in regard to observations along
the coast and to ringing birds.
I have to thank Miss E. P. Leach and Mr. H. F. Witherby for
furnishing me with the localities in which a number of birds
was recovered.
SYSTEMATIC LIST OF SPECIES FOR WHICH THERE ARE
MOVEMENTS AT LIGHT-STATIONS OR RINGING
RECOVERIES.
The Hooded Crow, Carrion-Crow, Rook and Jackdaw have
been grouped together, as it was not always clear from the
reports, which species was referred to. It is probable that
few, if any, Carrion-Crows were seen. The House and Tree-
Sparrows are similarly treated, but it is probable that most of
the birds were the latter species. The black ducks were not
specifically identified, but probably both Scoters were repre-
sented. In the B.O.C. investigation double dates, thus 9/10,
were used to indicate night migration. Letters in brackets,
preceding ring numbers, indicate the station, of which the full
titles can be found in "British Birds," V. 25, p. 111. All ringing
recoveries published to the end of 1935 are included.
The Raven. Corvus corax corax L.
Movements at light-stations.
Landguard L.H. 22nd June, 1884, two at 6.30 a.m. ; 17th