What can I do to stop my African Grey parrot from biting his toenails?

This isn't as unusual as you may think for a Grey. Sometimes they do this or over preen or pluck their feathers.

It could no problem at all and you may be able to get a lava perch or sand perches to wear the point of his nail off. Or there may be a medical problem or it could be a behavior problem.

I would first get a well bird check up from a Avian Vet. To rule any medical problems out. Example I knew a lady whos Ekkie started chewing his own leg. When taken to the Vet he was in pain in his legs(long story).

If he checks out.Start looking a his environment through his eyes. Example: Could he be to close to window and seeing outdoor birds which are scaring him.

Sun shining in a window casing shadows that are different than several months ago? Etc......

Neurotic behavior is common in larger parrots. Sometimes it comes in the form of screaming, plucking, and in this instance, constant pedicures. Usually this type of neurotic behavior is reinforced by the owner.

It will probably take a very long time to curb this. Firstly, do not react in any way to his nail chewing. Don't correct him, act like you don't see it. Sometimes when parrots try something, the owner reacts loudly, "hey stop that!" and gets excited. So the parrot repeats the action to try to get the same result. It becomes a habit.

Do not try spraying any bitter apple or fooey or anything else on his tootsies. Parrots have about 400 taste buds, and tend to enjoy strong tastes because there isn't much they DO taste.

Get a cement perch (I recommend a pedi perch) and put one, JUST ONE in his cage as the topmost perch. Hopefully that will help keep them a little more filed in the meantime. You don't want more than one filing type perch in the cage because it could eventually rub sores onto his feet.

It's natural for him to trim his nails to keep them sharp. It's necessary if he were living in the wild and is instinctive. What I have done is get some of those colored cement perches that gradually take the sharpness off as he uses them. There are also trimming sissors that are for the beak and nails, but I'm afraid to use those because I don't want to accidentally trim the nails too short and cause bleeding.

They do this to trim them and to clean them + sharpen, they will continue to do this until you clip them, and if you don't have experience in that I would take him to a professional or a vet do it. They may even still continue this because of their natural instincts. If they get too long it will become uncomfortable for them and so they bite them down.

Does he feel threatened by anything? Its sounds like a defence mechanism. Any new animals or anything like that around?

make so everything he stands on files his nails,and no that doesn't sound normal

ducttape his beak