NORTHERN BLACK-THROATED BLUE WARBLER 229 



is quite a little variation in the markings, ranging from spots and 

 undertones that are distinct and clearly defined to spots clouded 

 together and undertones only faintly discernible. The markings are 

 usually concentrated at the large end, often forming a loose wreath, 

 or sometimes a solid cap of brown. Occasionally, markings are well 

 scattered over the entire egg. There seem to be two distinct types, 

 one having spots of two or three shades of brown, with gray under- 

 tones, the other with tones of only one shade of brown, with drab 

 undertones. The measurements of 50 eggs average 16,9 by 12.8 milli- 

 meters ; the eggs showing the four extremes measure 18.9 by 13.0, 16.7 

 by 13.5, 15.2 by 12.2, and 17.0 by 11.8 millimeters (Harris) . 



Toung. — The period of incubation for the black-throated blue 

 warbler, according to Miss Stan wood's notes, is about 12 days; and 

 the young remain in the nest for about 10 days. Incubation of the 

 eggs and brooding of the young is done by the female only, but feed- 

 ing the young and cleaning the nest is shared about equally with the 

 male. She saw the young fed with daddy-longlegs, white moths, 

 caterpillars, crane-flies, mosquitoes, and many other insects. 



Quoting from the notes of J. A. Farley, Mr. Forbush (1929) gives 

 the following picture of a brooding female: "She had spread the 

 white feathers of her lower parts out so completely over her young 

 that there was not a vestige now visible of the four young that I 

 had found a short time previously filling the nest so full. She 

 'fluffed' herself out so as to hide all traces of the young. * * * ghe 

 made a beautiful picture. The whole effect was wonderful. The bird 

 seemed to be sitting in a billowy mass of eider down, or cotton wool, 

 that swelled, or rather bulged, up all around her, a regular bed of 

 down." 



Mrs. Nice (1930b) watched a brood of young black-throated blue 

 warblers, in Pelham, Mass., for 7 consecutive days, June 24 to 30, and 

 for a total of 361^ hours. During this time the female fed the young 

 193 times and the male, 201 times ; the average feeding time was once 

 in 5.6 minutes; the female brooded 22 times, a total of 200 minutes, 

 mainly in the earlier half of the period ; the feces were eaten by the 

 female 6 times and by the male 13 times ; they were carried away by 

 the female 47 times and by the male 67 times. 



As to the food of the young, Mrs. Harding (1931) writes : 



As soon as the young hatch the female begins feeding them. I have seen 

 no evidence of regurgitation. She thoroughly crushes caterpillars, etc., between 

 her mandibles before giving them to the young. Their food for the first day 

 consists of small insects, soft white grubs and a large number of half inch, 

 smooth, green caterpillars, which are found on hemlock trees. From the second 

 to the eighth day their diet consists chiefly of small green caterpillars, insects, 

 white grubs and an occasional may-fly or gray and cream colored caterpillar 

 without spines. On the ninth and tenth day their diet still includes white grubs 

 981873—53 16 



