Bumblefoot is a type of foot infection to which birds and rodents are prone. The footpad swells up and may even bleed or scab. It isn't totally certain what causes bumblefoot, but the general consensus is that it has something to do with unhygenic conditions and walking over abrasive or difficult surfaces.
I'm not sure about birds, but for this reason, many responsible owners of rats and other rodents will lay felt, newspaper or tile over the wire floors of their cages and only give their critters solid wheels, not ones made from wire mesh.
Treatment generally involves making sure the affected animal's environment is clean and the surfaces are covered with something soft enough as not to provide further irritation. For birds, the perches are covered with bandages or other soft materials. I saw a video of a baby penguin at a zoo with bumblefoot, and its keepers had given it some nice thick socks to wear.
It's definitely a vet-worthy condition, as it can worsen significantly, and it's normal for antibiotics and anti-inflammatories to be prescribed.
Picture: http://i.imgur.com/1KJ2K.jpg