186 BRITISH BIRDS. - 
Both male and female assist in the process of excavation, which usually 
occupies only the early hours of the day, the rest being devoted to coursing 
through the air in search of food. The little creatures begin by forming 
a small hole with their bills as they cling to the surface of the bank, some- 
times with head downwards. As this hole increases in size they stand in 
the excavation, and throw out all the loose sand or chalk with their feet, 
boring away at times as much as four feet into the solid bank, but at 
others only two or three feet. In some cases a single pair of birds 
make two or three holes before they are suited. Occasionally a large 
boulder stops the way ; or perhaps the sand is too hard or too soft ; whilst 
many holes are abandoned at a depth of a few inches for no apparent cause 
whatever. The birds seem well aware of the principles of drainage, and 
provide for it by making their holes slant slightly upwards. The holes 
vary considerably in size and shape; some will run almost straight, others 
turn to the right or left, not in acute angles, but seemingly by accident or 
to avoid obstructions in their way. Sometimes the holes are perfectly 
round, at others they will be rectangular, and often oval, and are usually 
two or three inches in diameter. The end of the hole is widened and 
hollowed into a kind of chamber, about six inches in diameter; and here 
the nest is formed. It is usually very slight—a mere bed of dry grass, 
coarse twitch, a few straws, and lined with one or two large feathers. The 
eggs of the Sand-Martin are from four to six in number. They are 
scarcely so polished as the eggs of the House-Martin, but are as pure a 
white, and vary in length from °76 to ‘62 inch, and in breadth from 
51 to ‘46 inch. 
Early in June or late in May, in favourable seasons, is the time to 
collect fresh eggs of this bird; but many Sand-Martins have a second 
brood, which are rarely on the wing before the middle of August. Some 
of the colonies of these birds consist of enormous numbers, and on the 
front of the cliffs where they breed they have all the appearance of bees 
in the process of swarming. On the banks of the Danube, the Volga, and 
the great Siberian rivers the numbers are sometimes almost incredible. 
One of these colonies is a most animating sight; the air is full of birds 
coming and going, and in front of the nests the crowd is so great that it 
is difficult to understand how each bird can thread the labyrinth. The 
Sand- Martin is almost as nimVie on the wing as the Swallow, perhaps more 
so than the House- Martin; and, like both these birds, it often dips for a 
moment in the water as it skims over the surface to drink or to bathe. 
Now and then the birds cling to the face of the cliff, and the nearly fledged 
young often sit at the mouth of the hole to be fed by their parents. Sand- 
Martins are bold in defending their colony from intruders; and I have seen 
them leave the bank in a body to drive away a Merlin, which they pursued 
with great pertinacity. 
