THE BIRDS OF NORTHERN THAILAND 387 



ground) , all the while spreading and twitching the tail. The common 

 call note is a buzzing shi-shi-shi-shi in descending scale; the song, 

 a whistled sweet' ' -cha-chu-chu-chu-chu or chl' -chob-chdo-chdb, with 

 the opening note higher, the others uttered rapidly in a monotone. 



An example of March 6 had the gonads greatly enlarged. Juveniles 

 that had not yet completed the postnatal molt were taken April 4 and 

 June 4. Postnuptial molt is shown by specimens collected between 

 October 18 and 27. 



An adult female from Doi Suthep had the irides pale creamy; the 

 bill slate, with the extreme tip and the edges of the commissure horn ; 

 the feet and toes light horny brown ; the claws light horny yellow. 



The adult in fresh plumage has the center of the forehead and the 

 crown orange-rufous, this color intergrading on the nape with the 

 brownish olive of the remaining upperparts (the wings and tail more 

 olivaceous-brown) ; the lores blackish ; the sides of the forehead, the 

 supercilium, and the entire underparts sulphur yellow, the feathers 

 of the throat and upper breast with fine black shaft streaks, the sides 

 of the head, neck, and body and the under tail coverts washed with 

 olivaceous. 



MIXORNIS GULARIS LUTESCENS Delacour 



Lao Yellow-breasted Babbler 



Mixornis rudricapilla lutescens Delacour, Bull. Brit. Orn. Club, vol. 47, 1926, 



p. 18 (Bao Ha, Tongking). 

 Mixornis rubricapilla minor [partim], de Schauensee, Proc. Acad. Nat. Sci. 



Philadelphia, 1929, p. 533 (Chiang Rai, Chiang Saen). 



A form best known by this name replaces M. g. sulphured in the 

 lowlands of Chiang Rai Province, where, although definitely known 

 only from Chiang Saen, Chiang Rai, and Wiang Pa Pao, it is probably 

 common and generally distributed. 



Two specimens in postnuptial molt were taken at Wiang Pa Pao, 

 August 1, 1935. 



M. g. lutescens, in Chiang Rai and the adjacent parts of Kengtung 

 State, shows approach to sulphured, and some birds can be identified 

 only by locality. Typical examples differ from sulphured in having 

 the crown chestnut-rufous instead of orange-rufous and the mantle 

 rather darker, with a somewhat oily tinge. 



The continental races of Mixornis gularis are a most difficult group, 

 in which one form intergrades insensibly with the next, considerable 

 individual variation appears within any given population, and speci- 

 mens are subject to great alteration in color (in life resulting from 

 wear and sunlight, in death from "foxing" and fading) . In studying 

 such birds, it is wholly impossible to arrive at satisfactory conclusions 

 without examination of long series from critical areas and I am for- 

 tunate in having before me, in addition to the skins deposited in 



