THE BIRDS OF NORTHERN THAILAND 317 



My adult and subadult males show considerable variation in the 

 depth and extent of the chestnut-rufous below, but such variation 

 seems to bear no relationship to geographical areas and the darkest 

 birds are connected by intermediates with the palest. It seems certain 

 that Kleinschmidt's siamensis cannot stand as a valid form. 



I do not see how the chestnut-bellied nuthatches can be viewed 

 otherwise than as extremely saturate tropical representatives of Sitta 

 europaea. Although, in certain mountainous areas of the Indo-Chinese 

 Subregion, a form of the europaena-gvowp may seem to occur together 

 with a form of the castanea-group, the fact is that, at such places, the 

 two occupy quite distinct ecological niches, the former holding the 

 high summits, the latter the low elevations. 



The mountains of Indo-China are of insufficient altitude to have 

 produced any known example of that type of subspecific variation in 

 which, on a single peak, a lowland form has developed directly from 

 a highland form, or vice versa. Thus, in northern Thailand, we find 

 that montium, and neglecta are so distinct as to indicate a cognate, 

 rather than a direct, relationship : in short, the two are far more dis- 

 tantly separated in time than in space. It may be supposed that, in 

 the isolated southern races of europaea-type, we have relict populations 

 whose ranges, for whatever reasons, have been reduced to those few 

 peaks upon which a suitable combination of favorable circumstances 

 still obtains. In the castanea-group we have birds that, developed 

 under tropical conditions, have populated the lowlands, wholly sur- 

 rounding the islandlike areas still held by their distant relatives, and 

 that, wherever the hills proved to be unoccupied by some form of 

 europaea-type, have penetrated to higher elevations, to give rise to 

 montane races of their own type. 



SITTA EUROPAEA TONKINENSIS Kinnear 



Kinnear's Eurasian Nuthatch 



Sitta castanea toukinensis Kinnear, Bull. Brit. Oru. Club, vol. 56, 1936', p. 71 (Nape, 



Laos). 

 Sitta castanea neglecta [partim], Riley, U. S. Nat. Mus. Bull. 172, 1938, p. 315 

 (Doi Hua Mot). 



A specimen (labeled "female" but almost certainly a male) taken 

 by H. M. Smith on Doi Hua Mot, August 30, 1934, is unquestionably 

 of this form, which has not previously been recorded from Thailand. 



S. e. tonkinensis resembles neglecta but is somewhat larger and has 

 the coloration, both above and below, decidedly deeper in tone. The 

 male may at once be distinguished from that of any other race by its 

 having the basal portion of the under tail coverts conspicuously black, 

 not gray or slaty. 



