472 BULLETIN 17 9, UNITED STATES NATIONAL MUSEUM 



plies structural material and coincidentally marks out the safety zones on the 

 cliffs for the river supplies them constantly, irrespective of weather, a source 

 of the choicest mud, and building can be undertaken at any time. Swallows 

 also generally like to carry on their work in bright sun and a drying atmos- 

 phere that fixes the growing sub-structure before further accretions are added. 

 It may be however that the site is decided upon during or immediately after 

 a shower and perhaps the foundation is outlined before the drying clift's lose 

 their tell-tale moisture and is then left to be completed in better building 

 weather. However it is, whether occult instinct or empirical methods guide the 

 birds, there is here shown a most interesting adaptation to environment. 



The activities about a colony of cliff swallows during the time of 

 nest building are fascinating. Such a scene has been admirably de- 

 scribed by Coues (1878) in his account of the cliff swallows observed 

 in the Colorado Valley: 



Suddenly they appear — quite animated and enthusiastic, but undecided as 

 yet; an impromptu debating society on the fly, with a good deal of sawing 

 the air to accomplish, before final resolutions are passed. The plot thickens; 

 some Swallows are seen clinging to the slightest inequalities beneath the eaves, 

 others are couriers to and from the nearest mud-puddle; others again alight 

 like feathers by the water's side, and all are in a twitter of excitement. Watch- 

 ing closely these curious sons and daughters of Israel at their ingenious trade 

 of making bricks, we may chance to see a circle of them gathered around the 

 margin of the pool, insecurely balanced on their tiny feet tilting their tails 

 and ducking their heads to pick up little "gobs" of mud. These are rolled 

 round in their mouths till tempered, and made like a quid into globular form, 

 with a curious working of their jaws ; then off go the birds, and stick the pellet 

 against the wall, as carefully as ever a sailor, about to spin a yarn, deposited 

 his chew on the mantel-piece. The birds work iudefatigably ; they are busy as 

 bees, and a steady stream flows back and forth for several hours a day, with 

 intervals for rest and refreshment, when the Swallows swarm about promiscu- 

 ously a-flycatching. In an incredibly short time, the basement of the nest is 

 laid, and the whole form becomes clearly outlined ; the mud drys quickly, and 

 there is a standing place. This is soon occupied by one of the pair, probably 

 the female, who now stays at home to welcome her mate with redoubled cries 

 of joy and ecstatic quivering of the wings, as he brings fresh pellets, which the 

 pair in closest consultation dispose to their entire satisfaction. In three or 

 four days, perhaps, the deed is done; the house is built, and nothing remains 

 but to furnish it. The poultry-yard is visited, and laid under contribution of 

 feathers; hay, leaves, rags, paper, string — swallows are not very particular — 

 may be added; and then the female does the rest of the "furnishing" by her 

 own particular self. * • * 



Seeing how these birds work the mud in their mouths, some have supposed 

 that the nests are agglutinated, to some extent at least, by the saliva of the 

 birds. It is far from an unreasonable idea — the chimney swift sticks her bits 

 of twigs together, and glues the frail cup to the wall with viscid saliva ; and 

 some of the Old World Swifts build nests of gummy spittle, which cakes on 

 drying, not unlike gelatine. Undoubtedly some saliva is mingled with the natural 

 moisture of the mud ; but the readiness with which these Swallows' nests 

 crumble on drying shows that saliva enters slightly into their composition — 

 practically not at all — and that this fluid possesses no special viscosity. Much 

 more probably, the moisture of the birds' mouths helps to soften and temper 

 the pellets, rather than to agglutinate the dried edifice itself. 



