In the juvenal plumage flight feathers of the kites are brown, barred
with white, much different in appearance from the dark, slaty plumage
of adults. Bent (_op. cit._:67) stated that these barred flight
feathers are retained through the second summer, and he quoted Mr. G.
W. Stevens as having found kites breeding in this immature plumage. On
June 2, 1961, I attempted to determine the ratio of these yearling
kites to others in the population at the Park. Most of the kites seen
were in flight too far away to discern definitely whether or not they
were juveniles, and records were limited to those seen at relatively
close range. In a total of 108 records only 11 pertained to these
yearlings and the remaining 97 were identified as of adults. Beyond
doubt in the course of my counts some individuals were recorded
repeatedly, therefore the counts are not entirely acceptable. However,
on each occasion that kites were seen in numbers in early summer, the
adults greatly outnumbered the juveniles. The approximate nine to one
ratio of adults to yearlings seems much too high. Even if the
difference is much less than indicated, the high ratio of adults to
yearlings would seem to imply that the adults have a long life
expectancy. A rather improbable alternative is that some of the
yearlings remain in winter quarters or wander elsewhere rather than
accompanying the adults on the return migration to their breeding
grounds. Still another alternative is that the breeding season of 1960
was relatively unsuccessful, but this idea is negated by my own
observations at the Park in late 1960, as recently fledged young were
numerous then.
At the time of my visit to the Park August 21 to 24, 1961, all young
had recently left the nests and were able to fly. However, their
behavior was so much different from that of the adults that a reliable
ratio could not be obtained. The fledglings tended to remain in the
nest tree, or to make relatively short flights near it, while the
adults occupied with catching of prey for themselves and their young,
spent much of their time aloft. The adults were hence far more
conspicuous than the fledglings. However, it is my impression that the
fledglings were from one-third to one-fourth as numerous as the
adults. If this ratio is correct, and if all adults had bred, from
two-thirds to three-fourths of the eggs and/or nestlings must have
been destroyed. This rate of loss seems reasonable in view of the
known histories of nests observed in June and again in July, and of
the fates of birds' nests in general.