Moaner Birds

There are a pair - at least, they look the same - of seagulls who seem to have spent the last week or so constantly having sex on the roof of the house opposite the back of our flat. It's a bit of a boisterous affair; loads of squawking and AARK!! AARK!! noises, and all that seems to happen is one of the birds stands on the other ones back and squawks a bit, while the one that is getting stood on squawks a bit more. I'm glad I don't live in the house above which all of this is taking place. Plus, they seem to do it all the time. Four in the morning, eleven at night, middle of the day. There's no sleep for these randy bastards!

But what's confusing me, is how the hell do they actually, you know, manage it?

We've searched high and low on Google, and despite being a previous Young Ornithologist (they never taught us about good birdy loving), I have absolutely not got the foggiest idea how it all happens.

So could somebody please enlighten me? How EXACTLY do birds have sex?