314 BULLETIN 19 7, UNITED STATES NATIONAL ]VrUSEUM 



Single pairs are the rule, but I have found as many as six occupied 

 nests inside of a very small area, the nests being only a few yards 

 apart." 



J. Stuart Rowley writes to me: "There is an apple orchard in 

 Tulare County, Calif., at an elevation of about 4,600 feet, where I 

 have had an ideal chance to observe the nesting habits of this vireo. 

 Here it seems that apple trees are favorite nesting trees, and many 

 pairs breed here every year. The first week in June is the height of 

 the egg-laying time, and many nests containing eggs can be found. 

 Often a nest of cassini will be found in one tree, Avhile in the very next 

 tree not 20 feet away will be a nest of the western warbling vireo." 



In the Yosemite Valley, Grinnell and Storer (1924) found a nest 

 on May 22, 1919. "It was placed in an incense cedar at the edge of 

 Merced River. The nest was on a branch which extended out over 

 the rushing stream and was about 18 feet above the surface of the 

 water." Dr. Grinnell (1908) found another nest "twelve feet from 

 the ground in the lower outer foliage of an incense cedar grooving 

 among fire," in the San Bernardino Mountains. 



Eggs. — Cassin's vireo lays three to five eggs ; four is the usual num- 

 ber, but sets of five are not very rare. They are like the eggs of the 

 eastern races, white or creamy white, and sparingly spotted with dif- 

 ferent shades of light or dark or reddish brown, the spots apparently 

 averaging lighter and brighter browns than with the eastern blue- 

 headed vireo. The measurements of 40 eggs in the United States 

 National Museum average 19.4 by 14.3 millimeters; the eggs show- 

 ing the four extremes measure 22.4 by 14.7, 21.3 by 15.2, 17.3 by 14.2, 

 and 18.0 by 13.2 millimeters. 



Food. — A separate study of the food of Cassin's vireo was made by 

 Prof. F. E. L. Beal (1907), who examined the contents of 46 stomachs, 

 taken in every month from April to November. He says : 



The vegetable food, which was only a little more than 2 percent of the total, 

 was made up of leaf galls, seeds of poison oak, and a few bits of rubbish. Not 

 a trace of fruit was found. 



The animal matter amounts to nearly 98 percent of the whole. Hemiptera 

 are the largest item and amount to nearly 51 percent. The various families 

 represented are those of the squash-bugs, leaf-bugs, stink-bugs, shield-bugs, 

 leaf-hoppers, tree-hoppers, the jumping plant-lice, and scales. The latter are 

 represented as usual by the black olive scale, which was contained in four 

 stomachs. Caterpillars, with a few moths, are next in importance and form 

 more than 23 percent of the whole food. They were eaten in every month and 

 are evidently a favorite diet. 



[Hymenoptera] amount to over 7 percent, and are mostly wasps, with a few 

 ants. * * * Ladybird beetles were eaten to the extent of a little less than 

 6 percent, which is quite reasonable as compared with the record of the warbling 

 vireo. * * * Other beetles amount to a little more than 3 percent of the 

 food, and are mostly weevils and small-leaf-beetles (Chryson:elidae). A few 

 flies, grasshoppers, and other insects amount to somewhat more than 2 percent, 

 and these, with 4 percent of spiders, make up the remainder of the animal food. 



