Not all pairs of lovebirds are good parents, nor should just any pairs be used for breeding. From my own experience, the best lovebird parents were parent raised and fledged. That's not to say that mature, handfed birds can't be used in a breeding program because they most certainly can. However, I find that I have fewer problems using lovebirds whose parents have had full control of their upbringing. Whenever I have a problem pair, the easiest solution for me is to use "foster" parents. I have had an excellent success rate with this technique as long as I stay within certain criteria.
Reasons to foster eggs/babies include:
This can be handled in a couple of ways. You have the option of fostering fertile eggs to a hen with less than 4 fertile eggs in her own box or you can wait for the chicks to start hatching and actually foster babies. The eggs that are being moved need to hatch within the same time frame as the foster hen's own eggs. Most hens won't feed babies that hatch too far ahead/behind their own babies. Crop milk is only produced for a certain amount of time, so hatch range is important.
This can be very frustrating! The hen laid a clutch of eggs, sat well for the first 18 days of incubation time and then abandoned the eggs, most of which are fertile. Or, an egg starts to pip (hatch) and the hen removes just the hard calcium shell. The unhatched chick is still hours away from being ready to hatch, so it dies.
Even eggs that have cooled to room temperature can still possibly hatch if moved to another nest. If the egg is candled and the inside still has a reddish coloring, the chick is alive and capable of surviving. When I have to foster in this situation, I may or may not have the choice of placing the eggs within their own hatch range. Given no other option, I place the eggs so that they will hatch ahead of the foster hen's own chicks. Most foster hens usually won't kill chicks that hatch ahead of their own, but nor will they usually feed chicks that hatch too early. I know this in advance, so I can pull those babies for handfeeding. Placing foster eggs in the nest of a hen whose own babies are due to hatch ahead of the foster eggs is my last course of action. With other babies in the nest hatching first, the environment in the nestbox can become just unclean enough so that the fostered babies will die in the shell. If, by chance, they hatch, the babies will be very small in comparison to the other chicks in the box so the hen may not even notice them, let alone, feed them. This kind of fostering is always my last choice because it involves the highest risk.
An egg-peeling hen is a real challenge! I have no good explanation as to why this happens but it does. The chick is so close to hatching, yet so far away. Removing the outer calcium shell allows moisture inside the egg to evaporate so everything dries out. The chick isn't ready for the egg to be opened so it dies. A good pair of foster parents or an incubator are the only solutions to this problem. If the natural parents will care for the chicks once they have hatched, I simply pick a hen with eggs in her nest. A hen with a blank clutch is wonderful for this. I take all the fertile eggs and replace them with blanks. The eggs to be fostered may or may not end up in the same nest. I don't even care about hatch range because the object here is to give the chicks a chance to hatch and to keep the natural mother sitting on eggs. I don't need the foster mom to feed/fledge. I just need her to hatch the babies. Once the chicks hatch, I give it back to its natural mom and remove a blank egg. Once in a while, I have a foster hen that will start feeding a foster chick after it hatches. Many times, I will leave one chick with her, especially if she's had several blank clutches.
Sometimes my choice of fosters isn't a lovebird. I've had Bourke Parakeets feed baby lovebirds, although only for a short time because baby lovebirds have strong beaks that can damage the beak of a Bourke hen if they are left with the Bourke for too long a period of time. A week to ten days is about all that is safe for the Bourke hen. The object of this kind of fostering is simply a live chick!
Sometimes, hens don't realize that the baby that just hatched also needs to be fed. The nurturing instinct either isn't there or it hasn't matured. Choice here is to handfeed or foster. My first choice is always fostering, if I can. I look for a nest that has less than 4 babies about the same age and I add one more. I don't foster babies to hens that already have 4 babies or will potentially have 4 babies. Before I make the final decision to handfeed, I check to see if one of my hens has older chicks that I can pull for handfeeding and I foster a baby that way.
There is one other thing you can try if mom doesn't feed. Sometimes a hen is just immature and doesn't realize that babies need to eat. It can take a short period of time for realization to take place. Handfeeding the baby while still in the nestbox and leaving it there can give the hen a chance to get her bearings and realize that she has to care for her young. Hatchlings need to be fed every 2 hours round the clock for the first 5 days if you want to try this approach.
I have had a lot of success with fostering and many chicks have been saved that otherwise would have died. I've had babies hatch from eggs that I've picked up from the bottoms of cages where pairs were on breeder rest and the hen started to lay. My fostering technique is not species specific, either. I find that, as long as I know my own birds, I can foster almost any lovebird species to any other lovebird species....as long as I stay within my own criteria.