How many times a day should I feed my 5-day-old baby pigeon?

18 days old is still a bit too young for a pigeon to be on its own, so the parents should be still caring for it. It's possible that the other baby is ill, or the parents ARE still caring for it and you just aren't catching them in the action. If you feel the baby is truly sick, injured, or not being cared for by its parents, then seeking help from a local wildlife rehab center is best. Do not attempt to move the baby or care for it yourself as it could still very well be cared for by the parents.

This greatly depends on the type of bird, and the individual bird's needs. Birds may eat anywhere from 10-100% of their body weight depending on their nutritional needs. A good rule of thumb may be to try out 1/4 of your bird's body weight and adjust from there. However, it is best to determine how much is needed by monitoring your bird's crop size, how interested he is in the food, and how quickly he is digesting what you are feeding him. If syringe feeding, several smaller meals a day may be better tolerated than one large bolus, and can help prevent over feeding or harming the crop.

If your bird has been injured it would be best to have the injuries addressed by a veterinarian first to make sure they are not impeding his ability to eat and causing him to worsen. Your vet may also want to give fluids or other IV medications if he cannot eat properly or is too weak to. If he is able to eat food that is in a mash, you can offer something such as baby bird food in a syringe or his regular diet blended and then mixed with water. This will help provide him with more balanced nutrition while he recovers. Rice cereals don't provide as much nutrition as a diet formulated for birds would. Monitoring how full his crop is (it will feel like a balloon under his chin) can let you know if you're feeding enough or not.

You can definitely try to feed it, you will need to buy wet canned cat food such as Recovery or A/D (from your local vet) as well as a syringe, you will need to feed it every couple hours during the day (no need to feed during the night).

If you've never fed a young bird, it would be best to have an experienced avian veterinarian or bird breeder show you in person. It is easy to accidentally cause aspiration of food when feeding. The technique in this video below may work safely as opposed to syringe feeding. https://youtu.be/e1oJKA4KebI A veterinarian may be able to trim the beak so it the alignment is in a more natural state. If the bird is young enough, you may be able to correct the defect to a certain extent with proper diet, grinding and gentle traction or pressure.

If the baby's parents are still caring for it it is best to just leave it alone, especially if the bird is still acting normally. If you see any signs of illness such as lethargy, stumbling around, etc, it is best to contact a local wildlife rescue as this is a wild bird and they will best know how to care for it safely.

You are absolutely correct this kitten should be fed every 2-3 hours at this stage. It's always better to underfeed than overfeed. I will put a link to a PetCoach article which should help you with her care. Best of luck. https://www.petcoach.co/article/how-to-raise-orphan-kittens/