disappears instantaneously, either by taking to flight or by crouching on the ground, a manœuvre frequently practised during the breeding season, which lasts from the end of January to the end of February. During this time their hideous cry may be heard night and morning, closely resembling the hooting of an owl. The corsac lives in burrows of its own construction. The Mongols and Tangutans catch it by setting traps at the entrances of these holes.
Turning from the mammalia of Northern Tibet to the birds, we find a general deficiency of the latter. It was, to be sure, mid-winter when we were there, and the summer birds had all flown away; but at the best of times no great variety can be expected in this country, so variable and unfavourable are its physical conditions. During our two and a half months' stay here we saw but twenty-nine kinds, only one of which (Cinclus sp.) was new; the others we had seen in Kan-su and Koko-nor. The few we saw in Northern Tibet were mostly on the border, north of the Shuga, and between this river and the Murui-ussu they were very scarce.
The most common birds of Northern Tibet are: vultures (Vultur monachus, Gyps nivicola), lammergeiers (Gypaëtos barbatus), and crows (Corvus corax), all which appear as soon as an animal is slain; red-legged crows (Fregilus graculus), which collect in vast flocks during winter; sandgrouse (Syrrhaptes Tibetanus), larks (Melanocorypha maxima, Alauda albigula), linnets (Linota brevirostra), the last named probably only wintering here; also the Podoces hu-
