CHIMNEY SWIFT 273 



and during their mad dash, one, if not both, uses a peculiar note — a 

 line of chips, a chatter, then the chips again. This combination of 

 notes accompanies the height of the pursuit, and the swifter and closer 

 the chase the sharper and quicker the notes. It seems also that the 

 nearer the birds are to one another, the faster they fly. They may 

 fly sometimes, their wings almost touching, at a pace that seems reck- 

 less ; then the notes spatter out as if self control were lost, and at last, 

 as the pursuer overtakes his goal, he rises a little above her and lifts 

 up his wings, and there appears to be a moment of contact. 



The probability that the nuptial flight leads, at least sometimes, to 

 sexual contact in the air is increased by Sutton's (1928) careful study 

 of the swift. He says: "In this courtship flight, the pair of birds 

 may fly rapidly about, twittering loudly; suddenly the upper bird 

 will lift its wings very high above the back and coast through the 

 air, sometimes for several seconds, while the bird beneath may soar 

 with its wings held in a fixed position below the plane of the body. 

 It may be that this graceful and interesting display is at the cul- 

 mination of courtship activity." 



From the fact that swifts in the courting season so often fly three 

 together when engaged in their pursuits — in the initial part at least, 

 for at the culmination the pair find themselves alone — a surmise has 

 arisen that one male and two females make up the trio and that the 

 swift is polygamous. This surmise, however, is not yet attested by 

 any conclusive evidence. 



Nesting. — Of the few North American birds — and they are very 

 few — that were influenced favorably by civilized man when he set- 

 tled on this continent, the chimney swift received the greatest bene- 

 fit. Before the coming of man, the swifts had been building their 

 nests for thousands of years in hollow trees, here and there in the 

 American wilderness. Then man came, and unwittingly supplied, 

 within his chimneys, exactly the situation the swift required for nest- 

 ing, an upright surface inside a cavity, protected from the weather — 

 the equivalent of a hollow tree. Thus the birds' nesting sites were 

 increased a millionfold. 



Nowadays the typical site is in a chimney, "from near top to 22 

 feet below it," Forbusli (1927) says. Yet, as the following quota- 

 tions show, the swift occasionally avails itself for nesting purposes 

 of some other of man's works; also from time to time it is found 

 breeding in its ancestral manner. 



The nest itself is a little hammock — half-saucer-shaped — composed 

 solely of dead twigs, which the bird breaks off as it flies past a tree. 

 The twigs are attached to the wall, and the twigs themselves are fas- 

 tened to one another by the glutinous saliva of the bird, which 

 hardens and fixes the structure so firmly to its support that it with- 

 stands, as a rule, the rain of summer storms. 



178223—40 24 



