BLACK-TAILED GNATCATCHER 381 



which they would scold vigorously whenever encountered at any time 

 of year. The anxiety of some of the birds increased as the time ap- 

 proached for the young to leave the next, though their fear seemed 

 to be for their offspring rather than for themselves. The female of 

 1921, though sometimes distrustful, occasionally indicated a certain 

 curiosity by approaching silently to within arm's length or hovering 

 close above one's head. In foraging, when not engaged in nesting, 

 a pair usually pursued independent courses through the bushes, 

 though remaining not far apart; one male, however, would always 

 closely follow his mate from bush to bush. 



Voice. — The black-tailed gnatcatcher is less inclined to song than 

 is the western; in fact, I have never heard anything which could be 

 definitely so called. The ordinary call note resembles that of caerulea, 

 but it can be recognized by a rather querulous, mewing tone; that 

 of the female is especially thin and plaintive. On rare occasions, the 

 male has been heard to utter a short, harsh note like that of the 

 plumbeous gnatcatcher. 



Field marks.— Within the territory of this subspecies, it could 

 readily be confused with only two other species, the western gnat- 

 catcher and the bushtit, both of which resemble it in size, length of 

 tail, and gray color. From the former it can be distinguished by its 

 darker general coloration and narrower white tail edgings. From 

 the bushtit it differs in its longer bill, more slender form, white tail 

 edgings (except in very worn plumage), and more restless movements. 



Enemies.— Mr. Hanna (1934) says: "It was not until May 25, 1933, 

 that I found a nest of the Black-tailed Gnatcatcher * * * in 

 this vicinity parasitized by the Dwarf Cowbird," and adds: "It must 

 be that the Black-tailed Gnatcatcher has not suffered from the cow- 

 birds to any great extent in any locality, as Friedmann in his book 

 'The Cowbirds' fails to mention them as victims. In this locality 

 one of the probable reasons for their escape has been due to their 

 usual habitat being on the dry bush-covered hillsides or dry washes 

 between 700 and 2,000 feet elevation above sea level." On one 

 occasion at Azusa I saw a nearly grown cowbird following and being 

 fed by a black-tailed gnatcatcher. 



Upon visiting one nest which then held eggs, I found a good-sized 

 alligator lizard (Gerrhonotus scincicauda) resting immediately beside 

 the nest while the male bird incubated, apparently unperturbed. 

 The only inference I could draw was that the reptile was waiting 

 untij the eggs should be left unguarded. Probably with the return 

 of the female bird, one would have driven the lizard away while the 

 other protected the eggs; however, I removed the intruder to prevent 

 any untoward happenings. 



