Age Dimorphism

Now listen to part of a lecture on this topic in a biology class.
There's a bird, a sea bird found in North America, which lives near the ocean, called the gannet, and it's a good example of this. So this bird the gannet, when gannets are fully grown, their feathers are almost all white, and having white feathers helps them hunt for fish in the ocean, since it's difficult for fish to see their light color against the sky. But when gannets are born and up until they're a few months old, they actually aren't white. They have almost all black feathers. Now, for a while, scientists didn't understand why gannets would have black feathers for the first few months of their lives, but it turns out, there's a reason for young gannets to have dark feathers. You see, some adult gannets are very aggressive towards other adult gannets. They tend to attack them in their nests, biting and pushing them. Sometimes, the attack is so severe the adult gannet even falls out of its nest. But it turns out that since young gannets are black instead of white, their looks don't cause adult gannets to behave aggressively towards them. The adult gannets don't try to attack them. Well, this is good because young gannets aren't capable of flying yet their muscles and feathers aren't fully developed, so falling out of the nest would be really harmful.