140 THE NATURAL HISTORY OF SELBORNE. 
brood ; while the first flight, shaken off and rejected by their 
nurses, congregate in great flocks, and are the birds that are 
seen clustering and hovering on sunny mornings and evenings 
round towers and steeples, and on the roofs of churches and 
houses. These congregatings usually begin to take place 
about the first week in August; and therefore we may con- 
clude that by that time the first flight is pretty well over. 
The young of this species do not quit their abodes all together; 
but the more forward birds get abroad some days before the 
rest. ‘These approaching the eaves of buildings, and playing 
about before them, make people think that several old ones 
attend one nest. They are often capricious in fixing on a 
nesting-place, beginning many edifices, and leaving them un- 
finished ; but when once a nest is completed in a sheltered 
place, it serves for several seasons. Those which breed in a 
ready-finished house get the start in hatching of those that 
build new by ten days or a fortnight. These industrious 
artificers are at their labors in the long days before four in 
the morning. When they fix their materials they plaster them 
on with their chins, moving their heads with a quick vibratory 
motion. ‘They dip and wash as they fly sometimes in very hot 
weather ; but not so frequently as swallows. It has been ob- 
served that martins usually build to a northeast or a northwest 
aspect, that the heat of the sun may not crack and destroy 
their nests ; but instances are also remembered where they 
bred for many years in vast abundance in a hot stifled inn-yard 
against a wall facing to the south. 
Birds in general are wise in their choice of situation ; but 
in this neighborhood every summer is seen a strong proof to 
the contrary at a house without eaves in an exposed district, 
where some martins build year by year in the corners of the 
windows. But, as the corners of these windows (which face 
to the southeast and southwest) are too shallow, the nests 
are washed down every hard rain; and yet these birds drudge 
