18 BRITISH BIRDS. 



characters of its inhabitants. These facts furnish good 

 ground for the belief that bird migration, possibly already 

 incipient at this remote period, became emphasized and 

 mainly developed by the recession of glaciation in the 

 northern hemisphere. Nor is it improbable that some- 

 what similar climatic changes in past geologic times 

 afford a similar explanation of migration in birds and other 

 animals in the southern hemisphere. 



That birds, and many other animals, perform long 

 migrations at regular periods, is a fact not open to cavil. 

 It is also evident that a reasonable cause for these 

 periodic journeys may be assigned. Hence a large part 

 of the " mystery " that has hitherto enshrouded the 

 general subject of bird migration may be fairly regarded 

 as having been dispelled. 



The manner of migration, as regards season, routes, 

 and extent, is now also known with considerable detail 

 for a large number of species. There still remains for 

 consideration the much discussed question of how the 

 migratory hordes find their way. 



While we are unable to fathom the workings of the 

 bird mind, or to take the measure of their mental and 

 sensory equipment, it must be recognised that birds are 

 endowed with the ability to remember and recognise 

 landmarks, since otherwise it would be impossible for 

 them to return year after year to the same nesting site, 

 after months of absence and thousands of miles of travel. 

 With the abundant evidence we have of their ability 

 to remember landmarks and to revisit former nesting 

 sites, it seems unnecessary still to regard their ability to 

 find their way in migration as a " mystery." 



It is generally conceded that birds are endowed with 

 great sensitiveness to atmospheric conditions, and readily 

 recognise approaching changes in the weather. As was 

 long since made known by Cooke,* and has since been 

 repeatedly confirmed by independent investigation, in 

 Europe as well as in America, birds migrate from areas of 

 high barometric pressure to areas of low barometric 



* " Report on Bird Migration in the Mississippi Valley," 1888. 



