Migration is physically demanding - birds require quality habitats along migration routes to rest, replenish fat reserves and escape predators.
(is physically demanding - birds; require; quality habitats along migration routes to rest) (is physically demanding - birds; replenish; fat reserves) (is physically demanding - birds; escape; predators)
is physically demanding - birds is physically demanding - birds is physically demanding - birds
require replenish escape
quality habitats along migration routes to rest
fat reserves
predators