68 NUMBER OF BROODS 



wings frequent affords concealment for their nests. The Woodcock, 

 on the other hand, nests shortly after its arrival; possibly because a 

 site is at once available. 



Consequently, in addition to those physiological factors which 

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

 of the bird's year, the exact date of a bird's nesting appears to be 

 governed by (1) 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 will doubtless be 

 added other causes, as we become more intimate with the facts involved. 



Number of Broods. Why do some birds raise only one brood and 

 others two or even three? We should look for a partial answer to this 

 question in the length of time required by a species to rear a brood. If 

 the period from the beginning of the nest-building to the date when the 

 resulting young are able to care for themselves is so short that the 

 parents are still in the physiological condition incident to reproduction, 

 a second family may be expected, and under similar circumstances a 

 third may follow. The eggs of the English Sparrow hatch in about 

 twelve days, the young remain in the nest only about a week, and the 

 species is reported to have reared six broods in a season near New York 

 City, but this number is doubtless exceptional. Robins' eggs hatch in 

 thirteen days; the young leave the nest when about two weeks old, 

 and the species raises two or even three broods. But the eggs of Fish 

 Hawks, for example, require four weeks' incubation; the young do not 

 fly until about six weeks old, and the species is one-brooded. These 

 facts, however, fail to explain why many birds in which the periods of 

 incubation and rearing of the young are quite as short as those of the 

 Robin, should have only one brood. The time of a bird's arrival on 

 the nesting-ground doubtless has some bearing on the question, and we 

 should also take into account the time of return to its winter haunts, 

 without in the least being able to say why it should come and go at a 

 certain time. Still, among permanent residents and migrants, which 

 arrive and depart at about the same season, some are single-brooded 

 while others raise two or even three broods. For instance, of the former, 

 the Song Sparrow rears two and on occasions, three broods, while the 

 Chickadee has but one. Here size of the brood may be a factor. Among 

 migrants, the Robin is two- or rarely three-brooded, while the Purple 

 Grackle, which comes just as early and remains nearly as long, is one- 

 brooded. Possibly there are here temperamental differences not to be 

 explained by observable influences. 



The question, not infrequently asked, whether any of our migrant 

 birds nest in their winter homes, makes it necessary to add that a bird 

 has only one nesting-season, and with those species which rear more 

 than one brood there is no appreciable interval of rest between the first 

 and succeeding broods. 



A table of dates showing when one may expect to find full sets of 

 birds' eggs of the first laying near New York City is appended: 



