Some comments on Sitta nagaensis grisiventris Kinnear, 1920
Harrap (1996: 116) briefly discussed the two populations and remarked that the “birds from Vietnam average slightly darker dirty blue-grey on the underparts than those from Mt. Victoria”. In his description of this species, based not on the nominate form but on montium he described the “rear flanks” of the male as “deep brick-red” and those of the female as “rufous”. In grisiventris the two sexes present in the same way. He also gave the colour of the male underparts as purer grey than in nominate nagaensis, and thus essentially without buffy tones although, as he says, these are present in the female. The overall impression is of very slight difference. He did not give separate ranges of measurements for Burmese and Vietnamese populations and separate data sets for the two populations would be interesting. Unfortunately, too few specimens are reliably sexed to facilitate this.
The Tring collection (BMNH) holds 19 specimens, including the holotype, from Mt. Victoria collected by Lt. Col. Rippon between March 10 and May 2, 1904. The labels show that these were taken from 4500 ft. up to 8000 ft., very few being sexed at the time. The colour of the rear flanks suggests that 9 of the 18 paratypes are males and 8 are females, but in some specimens calling the sex on this character is a doubtful exercise as individual variation seems almost to close the gap. In the same collection there are 10 specimens from Djiring or Dalat, south-central Vietnam, collected between 1918 and 1939 (three from 1918 by Kloss – 2 males and 1 female, the rest from three different expeditions led by Delacour). The sexing of Delacour’s birds seems doubtful, two are unsexed and the others all said to be males. The most reliable female (BMNH 1922.214.171.1243) has much lighter rufous rear flanks than any bird from Mt. Victoria, but this could not be corrobated as general. Of the two unsexed birds, both from March 1927, one (BMNH 19126.96.36.1998) is a male by its flank colour and the other may be a female on the same character but the rufous is not quite so pale as in BMNH 19188.8.131.523. Two other characters suggest constant differences. First, the extent of brick-red or rufous on the flanks seems to be greater on Mt. Victoria birds than on those from the Langbian plateau; second, the Mt. Victoria birds are a paler, bluer grey above than those from Vietnam.
It does not seem appropriate to name the Vietnamese population on this limited evidence, but it will be good to examine the DNA of the two populations.