MIGRATION 91 



of the colder north, to whom the associations connected with it 

 are doubly strong, have tried in vain to excel. The Indian of 

 the Fur-Countries in forming his rude calendar names the re- 

 curring moons after the Birds-of-passage whose arrival is coinci- 

 dent with their changes. But there is no need to multiply 

 instances. The flow and ebb of the feathered tide has been 

 sung by poets and discussed by philosophers, has given rise to 

 proverbs and entered into popular superstitions, and yet we 

 must say of it still that ' our ignorance is immense '." 



The wandering hordes to which reference is here made are 

 all bent on the same errand. In the spring they seek their 

 breeding quarters, in the autumn they are hastening away to 

 more congenial climes wherein they may pass the winter. 

 Great Britain harbours large numbers of such migrants, which 

 find here a suitable breeding ground, or come to us in the 

 autumn to tide over the winter ; while some species merely 

 pass through on their way to other lands. Thus, from March 

 to May, while the birds that wintered with us silently steal 

 away for more northern latitudes, others crowd in to take their 

 place. In the autumn these movements are reversed. 



Before we endeavour to analyse the possible meaning and 

 origin of these movements, let us trace, so far as may be, 

 the extent of the journeys which some of these wanderers 

 take. 



Than the Swallow it would be difficult to find a more in- 

 structive example. The species known in Great Britain as the 

 Common Swallow {Hirundo rusticd) occurs also all over Europe, 

 Northern Asia and North America, but presenting in each of 

 these great areas characters sufficiently distinct to warrant re- 

 cognition as sub-specific, or geographical races, though some 

 prefer to regard them as true species. Be this as it may, these 

 birds in their seasonal wanderings all agree, as do migrants in 

 general for that matter, in taking a course due north and 

 south. Thus then the Swallows of these several regions keep 

 each to the land areas lying more or less directly north and 

 south of their range. That is to say, their latitudinal range is 

 relatively limited. The Swallows of Northern Europe go south 

 to Africa, those of Northern Asia {H. gutturalis and H. tytleri) 

 to India and Burma, and even farther southwards, occasionally 

 reaching Australia and New Zealand, while those of North 



