GNATCATCHERS. 85 



is composed almost exclusively of insects, which they hunt with untir- 

 ing energy from morning till night. Like the titmice and kinglets, 

 gnatcatchers are fitted by nature to perform a service which larger 

 species are unable to accomplish. There are hosts of minute insects, 

 individually insignificant but collectively a pest, that are too small 

 to be attacked by ordinary birds and are to.be combated by man, if at 

 all, only at great expense. It is to so deal with such pests that they may 

 not unduly increase that these tiny birds would seem to be especially 

 designed. Three species of gnatcatchers live within the limits of the 

 State of California. Two of them, Polioptila plumbea and P. cali- 

 fornica, are confined to the southern part, Avhile the third, P. ca-rulea 

 obscura, occurs locally throughout the State. The material for a 

 thorough discussion of the food of these birds is unfortunately not at 

 hand, but there is enough to show conclusively the nature of the 

 work they are doing, and to enable us to assign them their proper rank 

 among the friends and helpers of mankind. 



The food of the gnatcatchers is remarkably constant in character 

 throughout the year, varying but little from month to month. It is 

 probable that these birds have a preference for a certain diet, and 

 search till they find it. 



Only 30 stomachs of P. c. obscura and the same number of P. cali- 

 fornica have been examined, and their contents were so similar that 

 they may be treated as from a single species. 



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

 vegetable food whatever, and in only one did it amount to a respect- 

 able 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, grass- 

 hoppers, and spiders. Bugs (Hemiptera) constitute more than half 

 of the whole food, 64 percent. These belong to the families of stink- 

 bugs (Pentatomidse), shield-bugs (Scutellericbe), tree-hoppers (Mem- 

 bracidse), leaf -hoppers (Jassidse), and leaf -bugs (Capsidse), with 

 perhaps traces of several others. In one stomach were 20 percent of 

 black olive scales (Saissetia olece). All of these are harmful to trees 

 and other plants. Wasps and a few ants (Hymenoptera) are next 

 in importance as an element of the gnatcatcher's food, and amount 

 to over 16 percent of the whole. These birds, like the flycatchers, 

 take much of their prey on the wing, and it is probable that wasps 

 and small bees are captured in this way. Beetles of several families 

 were eaten to the extent of over 7 percent of the food, but no decided 



