﻿108 FIELD AND FOREST. 



As already intimated, there are very many collateral sujects grow- 

 ing out of ornithological science which are yet to be investigated ; 

 and it is to these minor, but none the less interesting topics that some 

 of our writers are devoting their energies. 



The present subject has attracted attention. Considering it of no 

 great importance, however, those who have written at all upon the 

 subject have contented themselves with simply chronicling the facts; 

 making few generalizations and prematurely abondoning the data 

 which, doubtless, they regard only as 



"Truths that wake to perish never." 



Nevertheless we have here a highly interesting and fruitful field of 

 study. Numerous are the changes that have been made and are still 

 making in the manner in which various species perform operations 

 peculiar to bird-life; moreover, the birds' susceptibility of being af- 

 fected by the slightest alteration in external conditions, lends an ad- 

 ditional zest to the elucidation of governing laws. 



A consideration of more than one of the numerous sub-heads em- 

 braced in our caption would lead beyond the limits of this article; 

 therefore our subject shall be variation incident to nidification. 



For illustrations we need not look far, as nearly all our common 

 species have adopted or are constantly acquiring new styles of living. 

 It must not be supposed that these changes are always permanent, for, 

 indeed, it is only in exceptional cases where benefit has resulted from 

 the departure, or where circumstances are against reversion, that any 

 permanence is exhibited in the new regime. 



The chimney swallow (Chaetura pelagica) was accustomed to roost 

 and breed in hollow trees before this country became as thickly settled 

 as it now is. Although it has not entirely forsaken its old haunts in 

 some localities, at the present day it generally incubates and roosts in 

 chimneys of abandoned houses, and not unfrequently in those of in- 

 habited structures. This change is ascribable to various causes, fore- 

 most among which is the gradual but sure depopulation of the forests 

 and consequent loss to the birds of suitable trees; and secondly, the 

 convenience of its adopted habitations, which are now more numerous 

 and accesible than its old abodes. The proximity of man, also, in- 

 sures protection from rapacious birds. This desire to take advantage 

 of man's powerful presence is shown by many of our smaller species. 

 One is struck with the almost total absence of small birds in the interi- 



