376 BULLETIN 196, UNITED STATES NATIONAL MUSEUM 



Externally the nest is composed principally of hemp-like vegetable fiber mixed 

 with small curled-up leaves of the white sage, Eurotia lanata, plant-down, and 

 fragments of spiders' webs. Inside the nest is lined with the same hemp-like 

 fiber, only much finer, and a few feathers. The cavity of the nest is cup-shaped 

 and rather deep. Externally the nest measures 214 inches in diameter by 3J4 

 inches in depth. The inner diameter is 1% inches by 1% inches in depth. Com- 

 pared with a nest of Polioptila plumbea Baird, now before me, from Arizona 

 Territory, it seems much better constructed and also somewhat larger. 



The nests at Azusa were deeply cup-shaped, sometimes slightly 

 constricted at the top, and were compactly and neatly constructed 

 of small pieces of grass, bark, fiber, paper, cloth, string, etc., and lined 

 with small feathers, rabbit fur, and soft cottony material. Small bits 

 of newspaper entered largely into the construction of one of them. 

 The interior measurements of three of these nests were 1% inches in 

 diameter by 1% inches in depth. Ordinarily only the top of the head 

 and the tail of the incubating bird project above the rim. 



The birds being permanently mated, the nest-building urge some- 

 times seems to develop long before the time for egg-la3^ing. About 

 March 1, 1921, a pair of black- tailed gnatcatchers started a nest 

 near the top of a low sumac bush about 2% feet from the ground. 

 The work proceeded rapidly at first, most of it done by the male, 

 and then gradually slowed up. By the middle of the month the nest, 

 which was ready for the lining, seemed to be deserted, and a week 

 later was found overturned and partially destroyed. This suggested 

 a search for a new nest, which was discovered a day or two later about 

 125 feet away in a clump of cactus and weeds, and about 2 feet from 

 the ground. It was complete except for part of the lining, which was 

 added to from time to time until finished, after which the birds 

 showed no further interest in it. 



On April 22, by following one of the gnatcatchers, I found a third 

 nest containing three eggs in a buckthorn about 250 feet from the 

 previous nest. The site was about 2% feet from the ground in the 

 midst of an unusually dense mass of twiggs. The young having left 

 this nest on May 12, an inspection on June 8 showed that a section 

 of it had been removed, and it was found that only a small portion 

 of the second unused nest remained. A search revealed a nest with 

 three eggs, about 50 feet away, and situated very similarly to the 

 last nest, but less thickly surrounded by foliage. This nest appeared 

 a little looser and bulkier than those built of new materials. 



In 1927 a nest was discovered in a buckthorn bush, at a height of 

 about 3 feet, the set of four eggs being completed April 7, two 

 days after the male was seen incubating two eggs. On April 26 the 

 four young, which had hatched within less than 24 hours on April 

 20 or 2 1 , were found dead in and around the nest, though the parents 

 remained in the vicinity. The next nest was about 200 feet distant, 



