28 
INTRODUCTION* 
which are at this time inefficient, continue their route from pond to 
pond, floundering over the intervening land by night, until at length 
they gain some creek of the sea, and finally complete their necessary 
migration by water. 
Birds of passage, both in the old and new continents, are observed 
generally to migrate south-west in autumn, and to pass to the north- 
east in spring. Parry, however, it seems, observed the birds of 
Greenland proceed to the south-east. This apparent aberration from 
the usual course, may be accounted for by considering the habits of 
these aquatic birds. Intent on food and shelter, a part, bending their 
course over the cold regions of Norway and Russia, seek the shores 
of Europe ; while another division, equally considerable, proceeding 
south-west, spread themselves over the interior of the United States 
and the coast and kingdom of Mexico. 
This propensity to change their climate, induced by whatever 
cause, is not confined to the birds of temperate regions ; it likewise 
exists among many of those who inhabit the tropics. Aquatic birds, 
of several kinds, according to Humboldt, cross the line on either 
side about the time of the periodical rise of the rivers. Waterton, 
likewise, who spent much time in Demerara and the neighbouring 
countries, observed, that the visits of many of the tropical birds were 
periodical. Thus the wonderful Campanero,* whose solemn voice is 
heard, at intervals, tolling like the convent bell, was rare to Water- 
ton, but frequent in Brazil, where they most probably retire to 
breed. The failure of particular food at any season, in the mildest 
climate, would be a sufficient incentive to a partial and overland mi- 
gration with any species of the feathered race. 
The longevity of birds is various, and, different from the case of man 
and quadrupeds, seems to bear but little proportion to the age at which 
they acquire maturity of character. A few months seems sufficient to 
bring the bird into full possession of all its native powers 3 and there 
are some, as our Marsh Titmouse or Chicadee, which, in fact, as 
soon as fledged, are no longer to be distinguished from their parents. 
Land animals generally live six or seven times as long as the period 
required to attain maturity 3 but in birds the rate is ten times greater. 
In proportion to their size, they are also far more vivacious and 
long-lived, than other animals of the superior class. Our know- 
ledge of the longevity of birds is, however, necessarily limited to 
the few examples of domesticated species, which we have been able 
* Casmarhynchos carunculata . 
