Odd bulge on birds neck?

I am nursing a little sparrow back to health and about a week ago I noticed an odd bulge by it's neck that looked to have the food it was feeding it inside. Sometimes it is very prominent and other times I'm not even sure it's there. I'm not aware of Sparrows storing food so I have no idea if it is normal and if it is, what the heck is it? If it's not normal, is it dangerous? It looks like this, although I could find no explication for the picture. a href="http://besgroup.org/wp-content/uploads/111133.jpg" rel="nofollow"http://besgroup.org/wp-content/uploads/1…/a