A Wave of Life. 65 



solemn hootings of innumerable owls. It is plain 

 that these birds have been drawn from over an 

 immense area to one spot ; and the question is 

 how have they been drawn ? 



Many large birds possessing great powers of 

 flight are, when not occupied with the business of 

 propagation, incessantly wandering from place to 

 place in search of food. They are not, as a rule, 

 regular migrants, for their wanderings begin and 

 end irrespective of seasons, and where they find 

 abundance they remain the whole year. They fly 

 at a very great height, and traverse immense dis- 

 tances. When the favourite food of any one of 

 these species is plentiful in any particular region 

 all the individuals that discover it remain, and 

 attract to them all of their kind passing overhead. 

 This happens on the pampas with the stork, the 

 short-eared owl, the hooded gull and the dominican 

 or black-backed gull the leading species among 

 the feathered nomads : a few first appear like 

 harbingers ; these are presently joined by new 

 comers in considerable numbers, and before long 

 they are in myriads. Inconceivable numbers of 

 birds are, doubtless, in these regions, continually 

 passing over us unseen. It was once a subject of 

 very great wonder to me that flocks of black-necked 

 swans should almost always appear flying by imme- 

 diately after a shower of rain, even when none had 

 been visible for a long time before, and when they 

 must have come from a very great distance. When 

 the reason at length occurred to me, I felt very 

 much disgusted with myself for being puzzled over 

 so very simple a matter. After rain a flying swan 



