THE MIGRATION' OF ANIMALS. 119 



fact that many birds will repair year by year to the same spot is of 

 extreme interest, if we consider that the migratory habits must have 

 yearly led them on journeys of many hundreds or thousands of miles 

 in extent from their British nests. The possession of a very decided 

 and definite faculty of " locality " is thus apparently possessed by 

 many birds. In virtue of this faculty, and the memory and affec 

 tion they retain for their habitations, such migrants will fly unerringly 

 from the Mediterranean coasts to the northern parts of our land or oi 

 Europe at large ; or may even rest in their old homes after a flight 

 which had its beginning in regions lying beyond the equator. Dr. 

 Jenner's well-known experiment on the swifts fully confirms the 

 accuracy of the ideas regarding the return of migrants to their old 

 resting-places. The famous physician having procured several Glou- 

 cestershire swifts, cut two claws from a foot of each specimen, and 

 thereafter liberated the marked birds. The nests were examined 

 annually, and for three successive years the marked swifts were found 

 each in its own nest ; one of the marked specimens being actually 

 found in its accustomed locality after a lapse of seven years. Even 

 if it should be suggested that it is difficult or impossible to identify 

 the birds of each successive year as the veritable occupants of the 

 nest during the preceding years, or that possibly the birds arriving 

 each year to occupy a given nest were different individuals of the 

 same species, the circumstances become more puzzling and extra- 

 ordinary on account of these very suggestions. For then we should 

 have to explain how birds communicate with each other, and the 

 nature of the mysterious bond which would thus be presumed to link 

 together the different individuals in an affection for a particular home. 

 Even on the supposition that the young in course of time might 

 occupy the nest of their parents, we should also have to postulate a 

 wonderful accuracy of instinct and a tenacious memory of locality. 



In connection with such instances of memory and affection for 

 particular localities, we must take into account the distances over 

 which birds have to travel a feature casually alluded to in the pre- 

 ceding remarks. It is also worthy of note that the extreme length 

 and magnitude of the journeys of many migrants bear an important 

 relation to the nature and causes of the migratory habit. The idea 

 of a simple adaptation to surrounding conditions would fully explain 

 the migratory habits of animals, did we find that they moved back- 

 wards and forwards within a limited area, and according as the 

 seasons and food were respectively favourable and plentiful. But so 

 far is this from the true state of matters, that one of the chief puzzles 

 of the zoologist is to account for the apparently needless extent and 

 magnitude of the journeys of many migrants, their change of area 

 being inexplicable, as already noted, on the supposition of seeking 

 a genial temperature or a favourable feeding-ground alone. 



