BIRD MIGRATION. 21 



day.* But all— even the Woodcock — also feed freely by day during the 

 migrations. 



The remainder of the wading, and all the swimming birds,! as far aslcan 

 ascertain, migrate indifferently, and more or less equally, according to circum- 

 stances, by both night and day. This again was to be expected when we 

 consider that they feed (again without exceptions, I believe) more or less 

 indifferently and freely at all hours, and are not accustomed to seek safety in 

 concealment. J 



Certain species of Ducks, as well as all the Loons, Grebes, and Auks do, 

 however, frequently or habitually elude their various enemies by diving. 

 Thus water is in one respect to them what grass, rushes, etc., are to Snipe 

 and Quail — a refuge from danger. This doubtless explains a fact which I 

 have often observed, viz. : that while most diving birds migrate freely by day 

 along otir coast, they invariably perform long overland journeys by night. 

 The reason is obvious. In the one case flying directly ovef a continuous 

 expanse of water they are able to avail themselves of its shelter at a moment's 

 notice ;§ in the other they would be quite without this resource, if suddenly 

 threatened or attacked. 



With the Geese and Ducks it is even possible to trace some connection 

 between the extent to which the different species migrate overland by day, 

 and the dependence which they place on diving as a means of escape from 

 danger. Thus I have found that species which never dive unless when 

 wounded, such as Geese, Black Ducks, and Teal, migrate much more 

 freely (overland) by day than do others, such as the Scaup Ducks, Golden- 

 eyes, and Old Squaws, which resort to diving if cornered or otherwise hard 

 pressed ; while inveterate divers, such as the Ruddy Duck and our three 

 Scoters, seldom if ever venture to cross a wide extent of land by daylight. 



It has been shown, I trust satisfactorily, that the manner of migration of 

 our birds is determined by one, two, or all three of the following considera- 

 tions, viz. : habitual manner of procuring food, disposition, wing power. 

 It evidently has little or nothing to do with relationship or affinities except 

 within very narrow limits. This is proved conclusively by such cases as 

 that of the Robin, which migrates largely, if not exclusively, by day, while 

 its near alHes, the spotted Thrushes of the genus Tiirdiis, are among our 

 best examples of strictly nocturnal migrants. 



* Diurnal land birds which migrate by night are, I think, without exception, positively inca- 

 pable of obtaining food after dark. 



t Except strictly pelagic species, whose habits in this respect are not definitely known. 



X The Wood Duck will often hide in rushes or among thick brush, but it is also exceptionally 

 nocturnal in its migrations. 



§ Several water birds will dive directly from on wing, if shot at, or suddenly threatened by a 

 Hawk. 



