They say vultures have featherless heads to keep clean, so they don't get blood and bits of meat stuck in their feathers.  But hawks, and eagles, and other carnivorous birds also have to deal with bloody prey, so how come they don't need a bald head as well?  

My first thought was that it had to do with disease, since carrion that's been sitting around for a while would probably have a lot more disease-carrying bugs and bacteria and things that they would not want to get in their feathers.  But eagles and hawks will eat carrion too if they find it, won't they?  Wouldn't that be a problem for them as well?

Thanks in advance for any answers!  This is just something I've been curious about for a while

I think that they main reason is that vultures have bald heads when birds of prey don't is probably down to the size of the animal being eaten. Vultures don't kill their own prey, so they have no limit to the size of the animal they feed on. This means that they may be feeding on something very large that requires them to get their heads deep inside the body cavity.

Hunting birds are limited to feeding on animals that they can over-power, which will mean something smaller than them. This means that they are unlikely to need to get their head inside the body cavity - they just rip out beakfuls at a time or swallow the prey whole. Obviously this is far less messy than sticking their heads into a large rotting carcass.

I agree with Paolo.

Also it's worth noting that the bald head crops up in both old world and new world vultures which based on current phylogenies are not (... someone correct me if I'm wrong...) particularly closely related. Bald heads are also found in other birds that specialise on carrion (e.g. the maribou stork). My take on this is that the loss of head feathers is something that has evolved multiple times among bird lineages that specialise on eating large dead animals.