[tielfan]

I have a baby cockatiel which is around 4 weeks

This is the age at which babies normally leave the nest so he's probably coming out on his own. At this point he should weigh as much as his parents or even more, so it would be very difficult for them to throw him out of the nest. Is he fully feathered now or is he stunted/underdeveloped in any way?

It's common for chicks to stay on the floor when they first leave the nest, and they often hunch down flat instead of standing up tall. I suspect that it's a "hiding from predators" sort of behavior. Laying on his back isn't normal. However "floor chicks" are usually very nervous when a human approaches them. Is it possible that he's rolling over on his back because he's afraid of you? My floor babies always act kind of spastic when I go to pick them up, although they don't actually roll onto their backs.

Sometimes parent birds don't quite know what to do with a floor chick. If they aren't feeding him down there, you can put him back in the nest from time to time. They'll probably feed him there. You can put him in the nest at bedtime too so he'll feel safe while he's sleeping.

 

[tielfan]

I'm sorry that your baby passed away. It had been severely plucked by the parents which isn't good. They may have been doing it to drive the baby out of the nest so they could start a new clutch, and if there are other babies in the nest the parents might be doing the same thing to them. I can't tell from the picture whether they had been feeding this baby properly or not - if srtiels comes to this thread she is much better it identifying these things. The baby might have left the nest on its own to escape from the parents' plucking, but if it didn't have proper wing feathers or was weak from not being fed, it might have fallen badly and been injured.

It's OK to change the litter in the nestbox, but I will go further than that and recommend that you completely replace the old box with a new nestbox that lets you look inside. The new nestbox will help you identify problems early so you can intervene before any more bad things happen. If there were any insects hiding in the crevices of the old box, they'll be gone too. Keep the eggs warm while you're making the changes, and if possible put the parents in a different place while you're doing it so they don't see the disturbance around the nest. If you put the new nestbox in the same place as the old one the parents will accept it even if it looks different than the old one - they're very motivated to take care of their eggs.

There shouldn't be worms/insects in the nest. If you can get fresh leaves from a eucalyptus tree that hasn't been treated with pesticides, you can put a couple of them in the nest - this is supposed to help repel insects but won't harm the birds, which nest in eucalyptus trees in the wild. 5% Sevin dust might get rid of the bugs too - it's a mild pesticide that srtiels (the most experienced breeder on this board) recommends for use in nestboxes and directly on the birds too if they have insects on their bodies.

If there are any more babies in the nest that are being plucked or not fed by the parents you will need to take them out and handfeed them. They should be fully feathered by the time they're 3 1/2 to 4 weeks old, and if they aren't then something is wrong.