26 Bird - Lore 



round, it is far more abundant and varied in the spring and summer than at 



other seasons. Then, with the coming of the rains, the trees renew their 



fohage, blossom and fruit; then insects become more active and far more 



numerous, and, coincident with these developments, the instincts of the 



nesting season become active in birds. 



Confining ourselves to the birds in which we are more particularly 



interested, we have seen that some species nest early and some late. 



„ , ^ , Why is this ? The character of the food of the young 



Food of the . ; , . , . • , 1 r 



IS the most obvious cause determmmg the exact date of a 

 young 1 • 1, ■ TT I 1 ■ 1 f 1 ■ 1 r 1 1 • 



bird s nestmg. Hence those birds of prey which feed their 



offspring on mammals or birds are our first nesters, while those birds which 

 rear their broods on insects or fruit nest later. 



But is not a bird's nesting time also dependent on whether it be 

 migratory or resident? This is a difficult question to answer, since 

 it is by no means easy to determine whether or not a species is resi- 

 dent, in the strict sense of the word. Among resident species, of not 

 dissimilar feeding habits, there is much difference in nesting habits. 

 The White -breasted Nuthatch, for instance, near New York city, 

 nests in the middle of April, while the Downy Woodpecker waits until 

 a month later. The Bluebird nests in the first half of April, the 

 Cedarbird the latter half of June. Just why this difference should 

 exist is one of the things we should like to know. Possibly a study 

 of the food of the young birds may answer the question. Some 

 migratory birds arriving in this latitude at about the same time also nest 

 at widely different dates. Robins and Red -winged Blackbirds come 

 from the South at about the same time, in late February or early 

 March; but the Robins nest nearly a month earlier than the Black- 

 birds. Here, again, the difficulty of distinguishing breeding birds from 

 transients complicates the problem; and only careful, prolonged field 

 study will tell us whether the first comers among these and other 



,7- , summer resident birds are breeding birds or migrants to a 



Nature of , . tt , • 



. more northern nesting resort. Haunt also exercises some 



influence in this case. The early-nesting Robins find 



favorable sites in evergreens long before the marshes the Blackbirds love 



afford concealment for their nests. The Woodcock, on the other hand, 



nests shortly after its arrival; perhaps because a nesting site is at once 



available. 



Consequently, in addition to those physiological influences which 



induce an annual nesting season as one of the phenomena in the 



cycle of events making the bird's year, the date of a bird's nesting 



appears to be governed by (i) the nature of the food of its young; 



(2) whether it is resident or migratory, though this remains to be 



determined ; and (3) the condition of its nesting haunts. To these 



