Nest-building is not commenced till the middle of May, and by this time many of last year’s nests, which they would fain repair, are tenanted by that abominable pest—the Sparrow. The nest is built entirely of mud, plastered bit by bit against the side of some house which has overhanging eaves. No straw is used to bind it together, but it is gradually built up to join the eaves till only a small hole is left as a doorway. The lining is composed of fine grass and many feathers, and the eggs, which rarely exceed four in number, are pure white. At least two broods are reared in the season, and then as the weather gets colder they gradually collect near rivers, where their food, in the shape of flies and gnats, is more abundant, till finally, after assembling like the Swallows in large flocks, they suddenly take their departure. The whole of the upper parts, except the rump, which is white, are glossy blue-black; the under parts, including the feathers on the feet, white. The tail is very slightly forked. The sexes are alike in plumage. The young resemble their parents, but lack the gloss and are consequently brownish. They may also be recognised by having white tips to the inner secondaries. Length 5·3 in.; wing 4·25 in. [Illustration: SAND-MARTIN _Cotile riparia_ Adult (right). Young (left)] THE SAND-MARTIN Cotile riparia (Linnæus) This hardy little wanderer, the smallest and dullest of the Swallow tribe, braves our climate ere the March winds have ceased. At first he is generally found in the neighbourhood of water, but he gradually spreads over the country and eventually assembles in the sand-pits or gravel banks, where he makes his home. Though not attaching himself to the dwellings of man, he is a sociable little bird and breeds in colonies, which are in some places very large. They nest in tunnels which they excavate for themselves in the perpendicular face of a sand-pit. These tunnels are straight and narrow with a slightly enlarged chamber at the end. Their length varies from eighteen inches to three feet, and the different passages occasionally meet and may be used in common by two pairs. A slight lining of bents and feathers are added, and the eggs, five in number, are pure white and somewhat pear-shaped. When the breeding season is over they scatter through the country, keeping largely to the courses of large rivers, and by the end of September have almost all departed to other climes. The sexes are alike and have the upper parts brown. The under parts are white, with the exception of a brown pectoral band. There is a small tuft of buff-coloured feathers above the hind toe. In the young the feathers of the back have pale margins. Length 4·8 in.; wing 4 in. THE GREENFINCH Ligurinus chloris (Linnæus)