Ducks famously turn drab and a little boring after they are done with courtship. Even a Wood Duck, a notoriously flamboyant species, looks a little drab and worn in what is politely called “eclipse plumage.” Feathers wear out and new ones have to grow in.
Other birds also move into alternate plumage; it’s just a little more subtle. Here’s a Ring-billed Gull that still in full breeding – “basic” – plumage.
Note the pronounced reddish eye-ring, the reddish gape and the mostly white feathering on the head is mostly white. The bill is fairly bright yellow, as well.
By comparison, the same species in basic plumage is subtly different.
Note the eye-ring is gone entirely, as is the reddish gape. The gray streaks on the head are much more pronounced, and get more pronounced still with wear. And the bill is more brown than yellow.
Some Ring-billed Gulls hang around Idaho all year. Idaho, as you may know, is some distance from the ocean, which is why these are not “seagulls.” Most winter in places like Oklahoma which, you will also recall, is not near the ocean. So maybe we can just move away from the whole “seagull” thing. They are “gulls.”