What is a doctor called who specializes in the treatment of heart conditions?

Some species of hummingbirds have different shapes of beaks that evolved to allow them to drink from certain flowers. the flower species have evolved to produce nectar that is tasty for the hummingbirds. this example is a type of . cuckoos lay eggs in the nests of other birds. the cuckoo lays eggs identical to the eggs of the host species, so the other bird takes care of it. this is an example of .