THE TWIN ISLANDS. 179 



to us. If, as has been supposed by many writers, the ' 

 hand of man, by clearing and by cultivating the surface 

 of the earth, contributes essentially to the greater uni- 

 formity in the temperature of climates, it is reasonable 

 to conjecture that the time will come when the periods 

 of the migrations of our birds will be more constant 

 and fixed. For in North America, especially the United 

 States, the progress of population, and of clearing and 

 cultivating the earth, is more rapid and immense than 

 in any other portion of the world." 



"Whether it is reasonable to conjecture or not, certain 

 it is, that our author did not correctly estimate the ef- 

 fects of that general deforesting of the country which 

 has taken place since he wrote, nearly a century ago. 

 The trees are gone ; the countless acres of ploughed or 

 weed-grown fields are here, and with them a climate as 

 variable as ever. The birds come and go, as of yore, 

 but with the same degree of uncertainty as to their ar- 

 rival and departure. The birds have changed far more 

 than the seasons, and so other causes have operated to 

 bring this about, or it is, at least, an indirect effect of 

 the climate. The destruction of the forests has affected 

 plant life ; this, of course, has its influence on insect 

 life, and the birds must come and go, as their food 

 supply determines. The change wrought is that migra- 

 tion has become less fixed and methodical than former- 

 ly — not more so, as Dr. Barton believed would be the 

 case; and when any species learns to live upon food 

 available at all seasons, it will probably cease to wander, 

 unless forced td seek a suitable nesting place in some 

 distant locality. 



