172 
BIRD-LIFE. 
Contrary to expectation the relative distribution of 
a bird does not always bear the same ratio to the power 
it possesses, in a greater or less degree, of changing its 
place of abode. We more often find that the best 
flyers are limited, comparatively, to a small portion of 
the earth; at the same time we may remark that they 
are, under similarly local conditions, replaced by forms 
closely allied to them. The first may be attributed to the 
capacity of a bird to undergo long journeys, because this 
renders it possible for it to return to its original dwelling- 
place, under any circumstances, after quitting it, at 
pleasure; its distribution, therefore, is rather an act of 
free-will than the result of any fixed law; yet a law seems 
manifest in the fact that, under similar conditions, a 
representative of a certain species will inevitably arise. 
Thus, the zone of distribution occupied by the Eagle, 
the Falcon, the Swift, and the Swallow, is, comparatively 
speaking, limited, and that of the Lammergeir is singularly 
so ; but we find in all quarters of the globe representatives 
of the former, and in all the high-lands of the Old World 
birds remarkably similar to the latter, while in the New 
World we have the Condor, which is, at any rate, allied 
to them. The first-named may be found in countries very 
remote from their native home. This we do not consider 
as the result of distribution, but rather look upon them 
as erratic travellers, or, it may be, cast-aways; just as we 
regard all migratory birds as strangers, when they appear 
for the time being, but without the intention of breeding. 
Notwithstanding this, there are emigrations among birds, 
which lead to a fixed colonization, in what are to them 
foreign lands. When I say, “ foreign lands/' I mean that 
certain districts did not possess the necessary conditions 
of life for certain birds, rather than that these countries 
