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 foliage, blossom and fruit: then insects become more actiie and far more numerous, and, coincident with these developments. the instincts of the nesting ason become active in birds.
Confiuing 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 is the most obvious cause determining the exact date of a bird's nesting. Hence those birds of prey which feed their
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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 \Vhiteebreasted 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 larch: but the Robins nest nearly a month earlier than the Black- birds. Here, again, the difficulty of distinguishing breeding birds from tra \ients complicates the problem; and only careful, prolonged field study will tell us whether the first comers among these and other summer resident birds are breeding birds or migrants to a 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 afiord 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
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