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 A Bi-Monthly Magazine of

Western Ornithology

Volume XXIV

[Issued December 19, 1922]

THE DEVELOPMENT OF YOUNG COSTA HUMMINGBIRDS

By ROBERT S. WOODS

WITH FOUR PHOTOS BY THE AUTHOR

HILE following the progress of a pair of young Costa Hummingbirds (Calypte costae) at Azusa, California, in May, 1921, I was impressed with their slow growth as compared with that of the smaller passerine birds; so, on finding another nest, on May 18, 1922, I kept as accurate a record as possible of their development. This latter nest (figure 46) was located about four feet from the ground on a lower limb of an avocado tree some ten feet in height. It contained the usual two eggs when discovered and for two weeks thereafter. On the morning of June 1 there appeared one black, grub-like young hummer, with stubby, triangular bill and a double row of yellowish down along the back, the body being otherwise bare. The afternoon of the following day the second egg was hatched. The egg shells were not removed from the nest. The bill of the newly hatched hummingbird is a little longer than the width at the base, light in color, and abruptly differentiated from the head, which is comparatively broad and straight across the front. The abdomen is reddish brown, and the sides as well as the upper parts are black.

On the morning of June 7 pin-feathers had appeared on the older bird and by the afternoon of June 8 on the younger also. The bills were longer by this time and more tapering from the head and were mainly dark colored. On the 10th the older one had assumed the peculiar position shown in figure 47, with bill pointing straight up. This attitude is apparently made necessary by the fact that the young hummer is too long for the nest, but not yet large enough to hold its head above the edge. On the 13th the feathers were becoming soft and fluffy-looking and the older bird could open its eyes, at least partly. By the 15th both birds were able to sit up and stretch their wings and view the surroundings.

When inspected on June 17 the older hummer appeared fully feathered except for the shortness of tail and wing feathers. The bill was about the length of the head and was still straight and conical in outline. On the evening of the 21st the older bird seemed alert and ready to leave the nest. Upon moving the limb on which the nest was placed both birds suddenly flew to neighboring trees thirty feet away. The younger, though it could fly from one tree to another,