SWIFTS; ESCULENT SWALLOW. 455 



motion during the long summer days is immense ; for they 

 often pass sixteen hours in vigorous continued flight, chasing 

 insects not only for their own support but for that of their off- 

 spring ; and as the rate of their movement cannot be estimated 

 at less than 100 miles an hour, their day's performance must be 

 at least 1,600 miles. When their flight is continuous in one 

 direction, therefore, as in their migrations, we see how im- 

 mense distances may be traversed, with little more than the 

 average amount of exertion. The Swift is among the last of our 

 Swallows in its arrival, and the first to depart. Two species are 

 known in this country ; of which the Black Swift is by far the 

 most common, the White-bellied or Alpine Swift being a rare 

 straggler. The Black Swift has perhaps the largest expanse of 

 feathers, in proportion to the size of its body, of any Bird ; for its 

 length is nearly eight inches, and its breadth across the expanded 

 wings eighteen inches, whilst the weight of its body does not 

 exceed an ounce. 



409. The Swallows and Swifts of other countries bear a strong 

 resemblance to our own in their general habits ; one of those 

 most worthy of notice is the Esculent Swallow of the Javanese, 

 by which are constructed the remarkable nests, that are so much 

 valued by the Chinese as delicacies for the table. The material 

 of these nests is not yet satisfactorily ascertained ; by some it has 

 been supposed to be a kind of sea-weed, which, by boiling or 

 steeping in water, may be wholly reduced to a jelly ; whilst 

 others consider that a secretion from the stomach or salivary 

 glands of the bird itself constitutes a large part of it. Fish 

 spawn, again, has been said to have been found in the substance 

 of the nests. Probably various marine substances of a gelatinous 

 character are employed by these Birds, which inhabit deep 

 caverns on the brink of the sea, where they assemble in large 

 numbers ; and these are united by the viscid secretion formed by 

 the Bird itself, as in our own Swallows. The collecting these 

 nests is a proceeding of great danger ; but a large number of 

 persons are employed in it, as may be judged from the amount of 

 them exported to China. About 27,000 Ibs. are annually trans- 

 mitted from Java ; and these are of the best quality. A still 



