CLOSED: Bird ID: some gulls I see in Santa Cruz, CA

Hi,

I took some pictures of gulls in Santa Cruz, CA (numbered from 1 to 5). Could you tell me what's the name of these gulls, and how do you tell the difference between them. I remember their feather color of the same species can be different in winter and summer. So I guess the best way of identifying a bird is based on the color of its beak?

Thanks,
Cui

I find my pictures are out-of-order. Please ignore the numbers in the pictures. I shouldn't add the numbers. Sorry about that!

Cui

All Western Gulls, different ages. Left to right (ignoring the red numbers!):
Third summer
First summer
Second summer
Adult
Third summer

Resin

Good thing Resin knew, 'cause I didn't have a clue. Looks like you got 'em covered Cui.

Hack