ON THE SUBMERGENCE OF WATEU-BIUDS. 



own progress upward, so that it shall at first only show its head and neck, 

 or only its bill, above water, and it can in this state, take in a fresh supply 

 of air, and this too in a single second, sufficient to enable it to take a long 

 dive before again coming up, as every one must often have observed. How 

 would it be possible for the bird to perform all this if it had gone down with 

 such a reduced quantity of air as must have been the case, had this been the 

 mode of accomplishing its purpose. 



I will now dismiss this hypothesis, and proceed to consider the second mode. 



2nd. — It might so compress its body as to condense the air in the various 

 cavities to such an extent, as to place it in the required condition. 



It is a well-known fact that if you condense a cubic foot of air into a vessel 

 already containing another cubic foot under the ordinary atmospheric pressure, 

 you do not increase the buoyancy of the vessel in water by the additional 

 quantity of air, but the contrary — ^you lessen it, and make it sustain less 

 weight in the water by somewhere about five hundred and thirty-five grains, 

 or a little more than thirty-three pounds. Now I cannot help thinking that 

 here we have the true solution of the difficulty in question. No one, I 

 imagine, will deny that if the bird has the power of compressing itself to a 

 sufficient extent, it must sink instead of swim. Let us now see whether it 

 would be possible for a bird to compress itself to such an extent as to be in 

 the condition of the vessel with the two cubic feet of air. To establish 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 breath 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 Virginian Rail, (JRallus 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 or 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 covers, 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 preserve themselves in times of 



