308 BULLETIN 196, UNITED STATES NATIONAL MUSEUM 



while another set has slight, fine markings of drab. The third set 

 has more superimposed markings of drab or buffy brown, heavier 

 on the large end, and in three of the eggs to form a small, faint wreath." 



The measurements of 45 eggs average 19.1 by 14.5 millimeters; 

 the eggs showing the four extremes measures 21.2 by 14.8, 19.0 by 

 15.3, 16.1 by 13.8, and 19.3 by 13.7 millimeters.] 



Young. — Incubation, according to Jourdain, is apparently by the 

 hen only, but information is scanty, and the period is about a fort- 

 night. Both sexes feed the young. According to Chislett (1933) 

 nest sanitation is the special duty of the male, but it seems rather 

 unlikely that the female never takes part. Jourdain states that the 

 young leave the nest at 14 days but are not then fully fledged. Only 

 a single brood is reared in the short Arctic summer. 



Plumages. — The plumages of the western form of red-spotted 

 bluethroat are described in detail by Witherby (1938, vol. 2) and 

 the eastern race, to which doubtless the American birds belong, is 

 described by Hartert (1910) as a large, dark, strongly colored form 

 with large red breast spot and with wing measurement of 75-80 

 millimeters. 



Witherby had not examined a nestling of the red-spotted form, but 

 describes one of the European white-spotted bluethroat (C. s. cyan- 

 ecula), which can safely be assumed to be similar, as having dark 

 slate-gray down, fairly long and plentiful, distributed on the outer 

 and inner supraorbital, occipital, humeral, and spinal tracts. The 

 mouth inside is orange, without tongue spots, and the flanges are 

 whitish yellow externally. The juvenal plumage is very dark with 

 light streaks. The upperparts are blackish brown, each feather with 

 a median buff streak broadening at the tip; the throat, breast, and 

 flanks are similar. The tail and wing quills are like those of the 

 adult, and the wing coverts have buff tips. In the first winter plum- 

 age the male resembles the adult male in winter but has less blue on 

 the throat, which is more or less whitish but may show some rufous 

 in the center, while the chestnut breast band is paler than in the adult. 

 The female is also like the adult, but the throat is whiter and lacks 

 the dark spots that the adult females show. The primary coverts 

 and outer greater coverts have buff tips in both sexes. 



Food. — Bluethroats are primarily insectivorous. Jourdain (1938, 

 vol. 2) notes: Diptera and their larvae (Culicidae, Tipulidae, small 

 black flies, etc.), Coleoptera and larvae, and also some aquatic insects. 

 Small snails are also recorded, as well as worms, and some seeds and 

 berries are taken in autumn. Gurney, quoted by Jourdain, mentions 

 AcocephaJus nervosus, Philaenus spumarius, and a shell of Littorina 

 rudis in the case of a migrant on the English east coast. 



Behavior. — Bluethroats are, generally speaking, skulking birds, 



