They knew it was spring when the wild duck flew north again, to Siberia. Early in the morning, when he got up to chop wood and light a fire, Rakesh saw the V shaped formation streaming north-wards, the calls of the birds carrying clearly through the thin mountain air.
Could you explain the me the emboldened parts?
The “V-shaped formation” refers to pattern the migrating wild ducks use to break the wind when flying over long distances. The more experienced birds take turns at the lead, and by switching the bird at the point of the “V”, act much like the bunched riders in a pelleton (?) during a cycling race.