380 BULLETIN 19 6, UNITED STATES NATIONAL MUSEUM 



Vegetable food. — Of the 60 stomachs three only contained any vegetable food 

 whatever, and in only one did it amount to a respectable percentage. This one 

 held 92 percent of seeds of some species of Rhus; another contained 8 percent of 

 unknown seeds, and the third a few bits of rubbish, which amounted to only 2 

 percent of the whole contents. The total vegetable matter in the 60 stomachs 

 aggregated less than 2 percent of the entire food. 



Animal food. — The remainder of the food, over 98 percent, is made up of beetles, 

 wasps, bugs, and caterpillars, with a few flies, grasshoppers, and spiders. Bugs 

 (Hemiptera) constitute more than half of the whole food, 64 percent. * * * 

 In one stomach were 20 percent of black olive scales (Saissetia oleae). All of 

 these are harmful to trees and other plants. Wasps and a few ants (Hymenop- 

 tera) are next in importance as an element of the gnatcatcher's food, and amount 

 to over 16 percent of the whole. * * * The only decidedly useful insects in 

 any of the stomachs were 2 ladybird beetles {Coccinella t. calif ornica) , which had 

 been eaten by P. californica. 



Observation of the foraging birds gives the impression that small 

 moths (not mentioned in the report) must make up a large portion of 

 the food. 



Behavior. — Though Professor Beal found the food of the two species 

 of Polioptila to be essentially the same, their methods of obtaining it 

 are not identical. The aerial activities which have earned for caerulea 

 its appropriate name "gnatcatcher" were rarely practiced by the 

 various individuals of californica which I have watched. If they ever 

 obtained any of their food on the wing, it was usually while hovering, 

 like a kinglet, to pick off an insect from a leaf or terminal twig. A 

 sound of the snapping of the bill would occasionally give the impression 

 of flycatching at other times were the birds not actually in sight. 

 Practically all their foraging consists of systematic search through 

 the branches of shrubs. They do not seem to care for water, either 

 for drinking or bathing. 



A peculiarity of these birds is then reluctance to leave their accus- 

 tomed surroundings. Neither orchard nor garden seems to offer 

 inducement to exploration; when they reach the boundaries of their 

 arid, brushy habitat, they seldom go farther. Their feeding territory 

 covers but a few acres, and throughout the year the pair may ordinarily 

 be found at any time with very little search. However, I have not 

 known them to remain more than about a year, after which they 

 moved on to parts unknown. 



These gnatcatchers showed very noticeable individual differences 

 in temperament. The 1921 male, notable for his solicitousness and 

 watchfulness, was also most fearless and trustful in his attitude toward 

 the spectator and the camera. Others evinced varying degrees of 

 timidity and suspicion, but none showed any sign of hostility or 

 resentment at these intrusions upon their family affairs, in marked 

 contrast to their actions toward trespassing birds or toward cats, 



