CHAPTER XVI. 



POWERS OF DIVING AND FLIGHT. 



The Depths to which Gannets Dive — Swimming — The 

 Gamiets' Flight — Gannets at Play — Movements Controlled 

 by Wind — Migration proper. 



Depths to which Gannets Dive. — The depths to which our 

 diving sea-birds — Divers, Guillemots, Puffins, Gannets and 

 Cormorants — have the power of penetrating under water, 

 when it is calm and clear, is by no means satisfactorily 

 known. When one of these birds plunges, or makes its dive, 

 the external pressure of the water would expel the air from 

 the body, or at least compress it, and this pressure would in- 

 crease with each yard of its downward course, until at length 

 its air-sacks would be spent, and great muscular exertion, 

 both by leg and wing, would be required to force its way 

 further downwards. One can hardly imagine that the Gan- 

 nets' air-cells would give it any advantage over Guillemots, 

 Cormorants and Divers in its descent through the water — 

 rather the contrary — but Gannets have the impetus derived 

 from a high plunge, and the force w4th which these heavy 

 birds strike the sea must be seen to be credited. Yet in the 



