1 8 THE MIGRATION OF BIRDS. 



to reed and osier beds to roost. In skimming to 

 and fro they often drink or bathe, and repeatedly 

 strike the surface with their wings ; this may have 

 suggested a disappearance beneath the surface. Of 

 course subaqueous hibernation as apphed to 

 amphibious animals is a different thing altogether, 

 and, it need scarcely be remarked, is a well-estab- 

 lished fact. Even terrestrial avian hibernation has 

 at least one grave difficulty to contend against, espe- 

 cially when applied to Swallows, the very birds, by 

 the way, to which it has been most widely attri- 

 buted. These birds undergo their annual change of 

 plumage during the months of February and March, 

 whilst they are in their winter quarters, and it is 

 scarcely conceivable that such a function could be 

 performed during a state of torpor ; although, in 

 the case of Swifts, it may be remarked, Gilbert 

 White suggested that they might perhaps retire to 

 rest for a season, and moult in the interval. Swifts, 

 I should say, however, moult twice in the year, 

 and very slowly. 



Strange, nay almost incredible as avian hibern- 

 ation is, however, it must always be remembered 

 that the evidence against it is purely negative ; and 

 that although it has not yet been sufficiently 

 established to satisfy the sceptical science of to-day, 

 it has never been refuted. Denials prove nothing, 

 and all we can say is, until more satisfactory modern 

 evidence of its truth is forthcoming, that birds are 

 probably capable of hibernating under exceptional 

 conditions, and may have done so, but this habit is 



