ON THE POWERS OF CERTAIN WATER BIRDS. 513 



the condition of the vessel with the two cubic feet of air. To estab- 

 lish this point, I will again quote from Audubon's " American Birds." 

 In speaking of a young bird of the Least Bittern {Ardea exilis) which 

 stood on the table while he made a drawing of it, he says, " Replacing 

 it on the table, I took two books and laid them so as to leave before 

 it a passage of an inch and a half, through which it walked with ease. 

 Bringing the books nearer each other, so as to reduce the passage to 

 one inch, I tried the Bittern again, and again it made its way between 

 them without moving either. When dead, its body measured two 

 inches and a quarter across, from which it is apparent that this 

 species, as well as the Gallinules and Rails, is enabled to contract its 

 breadth to an extraordinary degree." 



Here it is clear that this bird was somewhat in the condition alluded 

 to, and this, too, without much apparent inconvenience ; and I feel 

 convinced, the amount of compression which evidently existed in this 

 case would be abundantly sufficient to produce in a Water Bird the 

 difference between floating well out of the water and being merely 

 suspended in it. In another place, Mr. Audubon says of the Vir- 

 ginian Rail (Ralliis Virginianus) : " Like the two preceding species, 

 (R. elegans and crepitans), the Virginian Rail has the power of con- 

 tracting its body to enable it to pass with more ease between the stalks 

 of strong grasses and other plants." 



Now if these birds have the power of compressing themselves to so 

 great an extent to enable them to move easily in their coverts, is it at 

 all improbable that diving birds should have a similar power, and one 

 that would be of such great value to them in enabling them to pre- 

 serve themselves in times of danger. But further, when a man at- 

 tempts to dive, he takes a full inspiratiou first, and then, when diving, 

 he powerfully exerts all the large muscles round the body, I have lit- 

 tle doubt to produce instinctively the same effect that I suppose is 

 produced in the diving bird, namely, to bring the specific gravity of 

 his body nearer to that of the water, and so make the diving easier. 

 Again, Mr. Atkinson said that a Moorhen shot when diving instantly 

 ♦ rose to the surface, notwithstanding the lead he had put into it. But 

 why ? Simply because, the bird being dead, the act of volition by 

 which it compressed its body was gone, and the contained air instantly 

 assumed its usual bulk, and the bird its usual position. So in the 

 case of any bird diving from fear ; it rises to the surface with its body 

 in a state of" compression ; it at first only allows its head and neck to 



