The annual migration to the summer pastures generally starts from late April to May and back to winter pastures in October. Gyamtsho (1996) notes that the migratory yak herds of Dhur village in Bumthang are moved and rotated very meticulously among pastures based on years of experience. The number of days grazed in each pasture are carefully worked out for the whole of the summer (Gyamtsho, 1996). The exception is where the yak have to stay in a particular pasture all summer because the herder owns only that pasture.