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 j 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 cliSs 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 nimble 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. 



