Use the Following Information to Answer the Question(s)below

Use the following information to answer the question(s) below.
Two populations of birds with somewhat different colouration live on opposite sides of an island.The habitat between the populations is not suitable for these birds.When birds from the two populations are brought together,they produce young whose appearance is intermediate between the two parents.These offspring will breed with each other or with birds from either parent population,and all offspring of these pairings appear intermediate to various degrees.
-Many songbirds breed in North America in the spring and summer and then migrate to Central and South America in the fall.They spend the winter in these warmer areas,where they feed and prepare for the spring migration north and another breeding season.Two hypothetical species of sparrow,A and B,overwinter together in mixed flocks in Costa Rica.In spring,species A goes to the east coast of North America,and species B goes to the west coast.What can you say about the isolating mechanisms of these two species?

A) They must have strong postzygotic isolating mechanisms to spend winter in such close proximity.
B) They must have strong prezygotic isolating mechanisms to spend winter in such close proximity.
C) Their winter habitat has no bearing on their degree of reproductive isolation.
D) Reinforcement must be occurring when they winter together.
E) The winter habitat is much more hospitable than the summer habitat, so isolation occurs only in summer.