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 
flieht are, when not occupied with the business of 
propagation, incessantly wandering from place to 
place in search of food. They are not, asa 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 
F 
