128 THE ESSEX NATURALIST.
comings and goings are occurring another form of migration is
in progress. This is composed of the spring passage-migrants,
birds which are coming from an area south of Essex, where they
have been wintering to another to the north, where they will
breed. It is probable that many more birds participate in this
spring passage than we have knowledge of, as, for example,
individuals of the species which are summer-residents in Essex.
These migrations, which probably follow mainly a northerly route,
are not long completed before a return movement to winter
quarters is evident. This is heralded by the arrival of occasional
passage-migrants in the middle of July. About the beginning
of August the summer-residents commence to move in the
direction of their winter quarters. The autumn passage and
the departure of the summer-residents are completed about the
middle of October. The appearance of our winter-residents
synchronises with the departure of the summer birds, and this
influx is not completed until some months later. It is difficult
to give definite dates for the conclusion of the arrival of the
winter-residents, as this movement is so subject to altered
weather conditions. We have completed the cycle, but very
little can be said as to how the many birds make their entry and
their exit. It is fairly safe to say, however, thanks to the
enquiry of the British Ornithologists' Club, that most of our
summer-residents arrive on the south coast of England and
proceed overland to Essex. A few may arrive directly on the
Essex coast, but it is probable that such birds have followed
much the same route as the main body.
Migratory movements, unless they are on a large or prolonged
scale, are difficult to recognize inland. Much movement passes
unnoticed, and it is only by the absence or presence of birds that
we know that they have migrated. Migration at sea, particu-
larly of terrestrial birds, presents fewer difficulties, and it is to
this that we now turn our attention. It is not necessary to give
a detailed description of the coast of Essex, but I will remind you
that it is extensive, much broken up, and that it meets the
sea more to the west than Norfolk, Suffolk and Kent. That is
to say, there is a deep recess with Norfolk and Kent on opposite
edges and Essex at the bottom and a line drawn between the
extreme easterly points of Norfolk and Kent leaves the Essex
coast much to the west, the gap being filled by a wide expanse