She walked over and told me! Just kidding.
Last year there was a husband and wife who were filming and photographing seagulls daily for a little over a month. I got to know them and asked them questions about gulls. They were super knowledgeable about the many gull species and their ways. Very serious bird-watchers!
The gull in my photo is a Ring-billed gull. We have lots of those around here.
I was told you can generally tell male versus female via the differences in their plumage. Males have a slightly brighter plumage versus females. Males also have slightly larger heads and bills vs females. They are also a bit larger in size.
Spending time with that couple I learned a lot. They would ask me to identify males versus females. At first I totally sucked. They told me to just sit and observe the gulls. Over a couple weeks I got better at identifying who was who.
Prior to landing the one in my photo was flying around with a larger gull that had a brighter plumage. Plumage differences are slight and are best seen on sunny days. Together they landed nearby. The bigger one didn't come near me like the smaller one did.
So I am fairly confident that they were a pair. Or they were in courtship.
I also learned that gulls a monogamous and pair for life. While in the air and when they landed this female was also squawking a lot at the male. Pretty sure that's a common thing in all relationships. (just joking!!!

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I spend a lot of time watching the gulls. The way they are able to turn 180° on a dime at high speed amazes me. On windy days they are able to stop mid-flight with extended wings and just be motionless for a few seconds. I love how they glide over long distances in the the sky. It looks so effortless.
I would love to experience being a gull for a day.