INTRODUCTION. 15 
selves, it is the extraordinary that develops what is 
really in us. We give full credit to the cunning fox 
and wary trout, because we know them so well; we 
admire the caution of the crow, because it is set before 
us continually, and drift into the belief that these are 
exceptional cases; but it is not so, as will be found 
out when we know all other creatures as well as we 
know those that I have mentioned. Perhaps we 
never will, but this is to be hoped, for such knowledge 
will lead to a more humane treatment of them all, 
even the despised worms of the dust. 
It is so rarely that we meet with a person who is 
indifferent to birds that we may say of them that 
they are a necessity to our surroundings, unless pent 
up in town. Certainly when we walk afield and 
neither see nor hear them, there is a feeling of desola- 
tion that destroys the pleasure of an outing. The 
lusty growths of summer are not enough of them- 
selves : they are but the set scenes of a stage whereon 
no actor treads; but, on the other hand, we have but 
to place a singing-bird in a bare bush, and we forget 
that there are no leaves and flowers. 
Perhaps no one phase of bird-life has received 
more careful attention than that of migration. The 
word needs no definition, but the act still calls for 
considerable explanation. A very large proportion 
of the birds of this country pass their summers in 
the north and their winters in the south: this is called 
migration; but it is not a uniform matter, and the 
length of the migratorial journey varies exceedingly, 
and with some species it has materially shortened in 
recent years, or else the observers of a century ago 
