SHRIKES, WAXWINGS, SWALLOWS, AND TANAGERS. 127 



They are migratory, having extraordinary powers of flight, 

 and are almost constantly on the wing. " The habits of swal- 

 lows," writes Dr. Coues, " best illustrate the modifying influ- 

 ences of civilization on indigenous birds. Formerly they all 

 bred on cliffs, in banks, in hollow trees, and similar places, 

 and many do so still. But most of our species have forsaken 

 these primitive haunts to avail themselves of the convenient 



THE BAKN-SW ALLOW. 

 {After Biological Survey.) 



artificial nesting-places that man, intentionally or otherwise, 

 provides. Some are just now in a transition state ; thus, the 

 purple martin in settled parts of the country chooses the 

 boxes everywhere provided for its accommodation, while in 

 the West it retains the old custom of breeding in hollow 

 trees." On account of this adaptability to the environments 

 of civilization, swallows should be encouraged as much as pos- 



