Identity Crisis

I thought I was capturing images of a late brood of swallows being fed by a parent.

When I uploaded the images onto the computer, I realised all was not as it seemed.

What the **** is an adult sand martin doing hanging out with a bunch of juvenile swallows?
There it was squeezed in between two swallow chicks, presumably hoping to free-load off a generous parent.

Actually, while I was watching, it never either begged nor accepted food from the parent swallow. I have no idea what it was doing there though.

Has anyone seen anything similar before? Google didn't come up with anything.

More pictures of these fledglings on my Flickr account
http://www.flickr.com/photos/gen2/

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