.54; Dr. Jenner on the Migration of Birds. 



annual excursion, should so uniformly not only revisit this 

 island, but even select the same spot for its breeding place, is 

 certainly a wonderful occurrence. But if birds were not in- 

 stinctively directed to return to their old haunts, should we 

 not find them over-crowding some situations, while others 

 would be left desolate ? And would not this be the case if the 

 search of food was the object of their migration ? However 

 it may be admissible, in one point of view, to consider the 

 bird in its state of migration from this country, as a nearer 

 neighbour than at first might be conceived, if we may be-al- 

 lowed to consider distance, or space, in the instance before us, 

 as governed bv the power of progressive motion, of what con- 

 sequence is it to the swift, which, to use the animated expres- 

 sion of Mr. White, " dashes through the air with the incon- 

 ceivable swiftness of a meteor," whether he comes to us from 

 some neighbouring country, or the shores of Africa ? The 

 wonder excited by the return of these birds again to their old 

 nesting places, woidd at once cease, if we could believe what 

 has been asserted by some naturalists, and gained credit with 

 many, namely, that at the time they disappear from us, 

 they submerse themselves in ponds and rivers, and in this si- 

 tuation become totpid. If this idea had not been encouraged 

 and supported by some new hypothesis, I should hardly have 

 thought it necessary to have taken any serious notice of it ; 

 but as the matter now stands I will just state my opinion, 

 why I think it impossible for any birds to be disposed of in 

 this way. 



Permit me first to call to your recollection the season of 

 the year at which many of these birds disappear. It happens 

 when they feel no cold blast to benumb them, and when the 

 common food with which they are supported, is distributed 

 through the air in the greatest abundance. At such a time, 

 what can be the inducement to them and their young ones, 

 which have but just begun to enjoy the motion of their wings, 

 and plav among the sunbeams, to take this dreary plunge ? 

 And how is the office of respiration to be performed during 

 the nine months watery residence? The structure of the lungs 

 of birds differs not essentially from that of quadrupeds, and 

 therefore all communication with the atmosphere being cut 

 off from the first moment of submersion, the possibility of a 

 bird living nine months, or indeed as many minutes, under 

 water, appears to be totally irreconcilable with the nature of 

 their structure. I have taken a swift about the 10th of Au- 

 gust, which may be considered as the eve of its departure, 

 and plunged it into water ; but like the generality of animals 

 which respire atmospheric air, it was dead in two minutes. 



The 



