food along a river than elsewhere, and this is a consideration, for most
birds, in spite of the wonderful stories of thousand-mile flights, prefer
to rest and feed when making long migrations, and also those short shifts
of locality which temporary hard weather causes. A friend just back from
Khartoum tells me that he saw the storks descending from vast heights to
rest at night on the Nile sandbanks, and saw their departing flight early
in the morning, these birds being in flocks of hundreds and thousands.

By watching the river carefully for many years I have noticed that it is a
regular migration route for several species besides swallows. The first to
begin the "trek" down the river are the early broods of water-wagtails,
both yellow and pied. They turn up in small flocks so early in the summer
that one might almost doubt if they could fly well enough to take care of
themselves. On June 26th last summer nearly forty were flying about in the
evening, and went across to roost on the eyot. Later numbers of blackbirds
arrive, also moving down the river. Sand-martins, when beginning the
migration, travel down the Thames in small flocks, and sleep each night in
different osier beds. How many stages they make when "going easy" down the
river no one knows. But I have seen the flocks come along just before
dusk, straight down stream, and then dropping into an osier bed.

In the second week of September there is usually an immense migration of
house-martins and swallows down the river. I have already described what I
once saw on a migration night on Chiswick Eyot. Sometimes they go on past
London, and find themselves near Thames mouth with no osier beds or
shelter of any kind. Then they settle on ships. I was told that one
morning the craft lying in Hole Haven off Canvey Island were covered with
swallows, all too numb to move, but that when the sun came out the greater
number flew away towards the sea. The same thing happened on the windmill
at Cley, in Norfolk, a famous starting and alighting place for birds.