THE BIRD-LIFE OF LONDON 
similar to those of the preceding Swallows, but the flight 
is not so powerful, more hesitating and fluttering. It is 
rarely heard to sing, and its call is a harsh, twittering cry. 
It is always interesting to remark how readily birds avail 
themselves of any little advantage. For many years I knew 
that the Sand Martin frequented the brickfields between 
Wood Lane and the waste ground which the late Franco- 
British Exhibition occupied. But these fields are done 
away with now, and are being rapidly filled in. ‘The 
large sheet of water in the Stadium at the exhibition, 
however, provided a haunt for several pairs of Sand 
Martins, and the birds frequented this place all through 
the Olympic Games. They nest in other brickfields to 
the west of the exhibition site. ‘The Sand Martin feeds 
exclusively on insects. Itisjust as gregarious and social 
as its allies, breeds in colonies, and returns year by year 
to its old nesting-places. It also frequently rears two 
broods in the summer, laying in May and July. Unlike 
the House Martin, however, it makes its nest in a hole 
in a bank, boring a tunnel into the soft gravel or clay for 
several feet, and making a slight nest at the end of it, of 
dry grass and straws, lined with feathers. ‘The four or 
five eggs are spotless white. A colony of Sand Martins 
is very interesting. Birds may be seen flying to and 
fro before the face of the bank or cliff in which the 
nest-holes are bored ; others at intervals enter the tunnels, 
or leave them to join the flitting throng outside. When 
the young are reared the birds assemble into large flocks, 
which appear to have certain rendezvous, water of some 
kind, and here the scene is most animated. ‘They are 
preparing for departure ; each day the crowds increase, 
and roost at night in some reed- or osier-bed. The 
migration south begins in September, and continues into 
October. Odd birds even occur near London during 
November. I have seen this Martin as late as the middle 
of that month at Richmond. 
226 
