During migration the birds fly over 1000 of miles through hostile environmment to reach their winter resting spot.
(the birds; fly; over 1000 of miles; to reach their winter resting spot; T:During migration) (the birds; to reach; their winter resting spot)
the birds the birds
fly to reach
over 1000 of miles to reach their winter resting spot T:During migration
their winter resting spot