NORTHERN MacGILLIVRAy's WARBLER 537 



be clouded. On many, even the delicately marked types, are often 

 scattered a few spots, or small scrawls, of very dark brown or even 

 black. Occasionally, these scattered dark spots or scrawls are the 

 only apparent markings, the lighter browns lacking and the under- 

 tones almost imperceptible. While the markings are generally con- 

 centrated at the large end, there is not as great a tendency to form a 

 wreath as in many of the warblers' eggs. The measurements of 50 

 eggs average 17.8 by 13.6 millimeters ; the eggs showing the four ex- 

 tremes measure 19.4 by 15.1, and 16.4 by 12.7 millimeters (Harris) . 



Young.— The nest watched by Miss Wythe (1916) held four eggs 

 on June 13, on which the female had been incubating for an unknown 

 period ; on the twenty-third two of the eggs had hatched, and the third 

 egg hatched the following day ; the incubation period was, therefore, 

 at least ten days. When first hatched, the nestlings had "scarcely 

 a trace of down on them." One the following day, they "were now 

 scantily covered with down, a patch showing on top of the head, a 

 line down the middle of the back, and a tuft on the wings. * * * 

 On June 27 I spent an hour during the morning timing the feeding 

 of the three young birds, from a point about twelve feet distant. I 

 found that the female warbler came with food at intervals of from 

 three to five minutes throughout tlie hour. On the fourth day after 

 hatching, "juvenal feathers had appeared over most of the head, down 

 the center of the back, and on the wings. The eyes of one bird were 

 open. On the following day the eyes of the second bird were 

 open. * * * The sixth day showed juvenal feathers appearing on 

 the lateral tracts, and tail feathers just beginning to grow out. On 

 the seventh day, June 30, the wing feathers had broken through the 

 sheaths for about one-half an inch. The birds' heads were well cov- 

 ered with feathers, but the sheaths still adhered to the bases. The 

 contour feathers were in a similar condition. The tail feathers did 

 not show any further development. On July 2, the ninth day after 

 hatching, the two older birds left the nest, followed later the same day 

 by the third bird, the latter having been in the nest only eight days. 



Based on the findings at four nests, Grinnell and Storer (1924) state 

 that "eggs are laid on successive days, incubation begins immediately 

 upon the laying of the last egg or possibly before, and is completed 

 in 13 days, the young hatch on the same day, or on two successive 

 days, and leave the nest 8 or 9 days after hatching. The male seems 

 to participate but little in caring for the brood." 



PluTnages. — The molts and plumages of MacGillivray's warbler 

 parallel those of the mourning warbler and need not be repeated here. 

 In the juvenal plumages the two species are practically indistinguish- 

 able, except that the former has a longer tail. The differences in later 

 plumages are referred to under field marks. Dickey and van Rossem 



