No. 380.] YOUNG SPARROW HAWKS. 569 
distinctive. It would be interesting to ascertain if this is always 
the case among the Fadconide, or was only accidental in the 
present instance. Prof. Alfred Newton, in his Dictionary of 
Birds, page 634, says that owls often begin brooding as soon 
as the first egg is laid; “ but, if my observation is not mistaken, 
the habit is not constant, even with the same individual bird”’; 
and he adds, by way of explanation, that this “ practice unques- 
tionably has its advantages, since the offspring, being of differ- 
ent ages, thereby become less of a burden on the parents which 
have to minister to their wants, while the fostering warmth of 
the earlier chicks can hardly fail to aid the development of those 
which are unhatched, during the absence of father and mother 
in search of food; but most birds, and, it need scarcely be said, 
all those the young of which run from their birth, await the 
completion of the clutch before sitting is begun.” 
Bendire, in his account of this falcon in his Life Histories 
of North American Birds, says positively that the eggs “are 
deposited at intervals of a day,” but he has nothing to say about 
the alternation of the sexes in the brood. It is a well-known 
fact that the eggs of the sparrow hawk vary greatly in form as 
well as in their ground color and markings. As to this last, it 
may largely depend, as I have pointed out in my Comparative 
Oölogy of North American Birds, “ upon the physical condition 
of the parent bird at the time of depositing the egg.” * 
If it be true that the sexes alternate in broods of young 
sparrow hawks, as a regular thing, the present writer has no 
explanation for the fact, nor has he ever heard of one as having 
been advanced by any other observer, and it is more than prob- 
able that it will be a long time before science will. be in 
possession of the correct interpretation. 
In the reproduction of my photograph illustrating this paper, 
both the birds in the picture are females, they being the oldest 
and the youngest of that sex of the five; in other words, they 
represent birds numbers two and four of the brood. In order 
to photograph them I was obliged to build up the little plat- 
form of twigs, seen in the figure, for them to rest upon, as 
1 Report of U.S. National Museum, p. 476, 1892. This memoir is now entirely 
out of print. 
