INTRODUCTION. xlvii 



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 Dem- 

 erara and the neighboring countries, observed that the visits of 

 many of the tropical birds were periodical. Thus the wonder- 

 ful Campanero, whose solemn voice is heard at intervals tolling 

 like the convent- bell, was rare to Waterton, but frequent in 

 Brazil, where it most probably retires to breed. The failure 

 of particular food at any season, in the mildest climate, would 

 be a sufficient incentive to a partial and overland migration 

 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 propor- 

 tion to the age at which they acquire maturity of character. A 

 few months seems sufficient to bring the bird into full posses- 

 sion of all its native powers ; and there are some, as our Marsh 

 Titmouse or Chickadee, which, in fact, as soon as fledged, are 

 no longer to be distinguished from their parents. Land ani- 

 mals generally live six or seven times as long as the period 

 required to attain maturity ; 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 knowledge of the longevity of birds is, however, 

 necessarily limited to the few examples of domesticated species 

 which we have been able to support through life : the result of 

 these examples is, that our domestic Fowls have lived twenty 

 years ; Pigeons .have exceeded that period ; Parrots have at- 

 tained more than thirty years. Geese live probably more than 

 half a century ; a Pelican has lived to eighty years ; and Swans, 

 Ravens, and Eagles have exceeded a century. Even Linnets, 

 in the unnatural restraints of the cage, have survived for four- 

 teen or fifteen years, and Canaries twenty-five. To account for 

 this remarkable tenacity of life, nothing very satisfactory has 

 been offered ; though Buffon is of opinion that the soft and 

 porous nature of their bones contributes to this end, as the 

 general ossification and rigidity of the system perpetually tends 

 to abridge the boundaries of life. 



