190 THE CONDOR Vol. XX1V 
had difficulty in securing a foothold and generally dropped to the ground. It 
made no attempt to escape when picked up and when finally replaced in the 
nest, aS an experiment, it settled itself contentedly and remained there for about 
24 hours, leaving when I approached the nest the next evening. At that time 
its flight was stronger and it seemed well able to care for itself. 
For purposes of comparison I noted the approximate time spent in the nest 
by the young of several common birds nesting at about this same time. These 
were the House Finch (flve nests), Green-backed Goldfinch, Western Lark 
Sparrow, Anthony Brown Towhee (two nests) and Western Mockingbird. The 
leneth of time ranged from 10 to 16 days, the longest in the case of the Moek- 
inebird and perhaps one of the Linnets, the shortest for the Lark Sparrow and 
Towhee, which probably left their nests rather prematurely. These figures are 
Fig. 46. Nest (no. 2) oF CostA HUMMINGBIRD. AZUSA, CALIFORNIA, 
May 19, 1922. 
not intended to be accurate, but they are in all cases considerably less than the 
20 days which the Hummingbirds required. The corresponding period for the 
brood observed the previous year was not determined exactly, but I believe it to 
have been 22 or 23 days. 
On June 2, 1922, I found another Costa Hummingbird building a nest near 
the end of a long horizontal limb of a good-sized avocado tree, at a height of 
about five feet from the ground. Her method was first to alight in the nest, 
then place the material under her (figure 48) and compact it by treading with 
the feet and turning about. Material for the outside of the nest was placed 
while hovering or while perched on a branch. On one occasion after leaving the 
nest the bird flew up to a twig a few feet above, whereupon I was surprised to 
see another hummer alight in the nest and rearrange some of the material, after- 
