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I was recently at a music festival in a field here in the UK. It was a nice hot day and I was staring up into the lovely blue sky. I noticed there were high numbers of seagulls circling above, seemingly riding thermals to a great height (they quickly became speks in the sky).

I started wondering, what are they up to? I couldn't make sense of it.

If they were riding the thermals as a mode of transport, they didn't appear to be going anywhere (just round and round in circles).

It didn't make sense that they were doing it to spot food either (that I thought). There was plenty of food about, but none of them appeared to be making any attempt to come down.

It almost appeared that they were simply riding the thermals for fun.

So why would these birds by seemingly riding thermals for no reason?

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For the same reason carrion birds circle over fresh kills: They're waiting for an opportunity to swoop in and get some food. All the gulls see is a large gathering of humans, which typically means dropped chips, bits of hotdog buns, discarded scraps, leftovers on tables, people throwing bits for the birds. Wherever you have big gatherings of large mammals there will be flocks of scavengers. You'll see the same behaviours in nature too, scavengers will follow herds of deer or caribou waiting for one of them to either drop dead or get picked off by a predator so they can swoop down to pick away at what gets left behind. The reason they ride the thermals and circle overhead is so they can conserve energy while they watch and wait.

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They are centering good thermal spots and picking up altitude so they're not putting any effort into flying while looking for food.

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