MIGRATION OF BIRDS. 151 
of soft insect food for their untledged young.” These are 
samples of the most worthy quotations that I have culled 
from my reading. 
To me, since boyhood, the subject has always been full of 
fascination, and I have formed ideas and re-formed ideas. 
My conclusions at present are not difficult to understand. 
To begin with, you have your centre or centres of distribution. 
As far as migration is concerned, it matters little whether 
you had a single pair of birds to be the parent stock of all 
subsequent species of birds, or had many pairs. Scientific 
research is in favour of the evolution of species. As long 
as there was abundance of food around the original centre 
there was no need for movement, and there would be little 
or no differentiation of species; but let the food-supply fall 
short through the increase of birds or through physical 
causes that may have sprung up, and immediately birds 
were called upon to exert themselves if they would survive. 
It may be that during some short period of hunger some in 
a favouring locality took to a new form of food for the time 
being. If the congestion continued, these birds that had 
taken to the new food of a certain locality would have to 
take to it for a longer period of the year, and naturally 
their bodily frame would alter to suit their new life, just as 
any man’s frame would who left one kind of work to 
take up another. In birds there would be a development 
in the hardness or softness of the beak, and in the structure 
of the feet, to suit tree-climbing or ground habits. There is 
a large family of birds in the Sandwich Islands that has 
- given ornithological classifiers much trouble. Some have 
classed them among finches, and some among honey-eaters— 
certainly very different opinions; but the trend of latest 
research into the, subject has been that, to begin with, the 
form was distinctly that of honey-eater, and that as food 
failed the birds took to insect-eating, and having to bore in 
the ground for these, or into rotten tree-trunks, the bills 
became hard. Jf birds should happen not to differentiate 
in their original centres, and had to continue the struggle 
for existence, they had to leave their haunts for a season— 
it may be, for a month or two; perhaps moved east or 
westward, keeping to isothermal lines as most likely to give 
