tao_li's Identifications

This snake was falling over 1.5 meters when i first noticed it. Possibly attacking or being attacked by a bird within a meter from it. Do snakes jump out of trees to eat? Seen after a couple days of heavy rain.

Observed this unique snake specimen for a good 10min on a hilltop overlooking Larung Gar buddhist college, Sertar county (色达 Seda in Chinese), Garze （甘孜 Ganzi), Sichuan province, China.
Sunny afternoon, altitude 4000-4100m.
Location indicated on Google Earth map should be correct, but if wrong then it is within 50-100m to the SW (going up the hill).
The snake could be approached easily and photographed, though it raised its head in a viper-like way at some point.