Why is my lovebird regurgitating undigested seeds? Is she sick?

She's regurgitating for the bird in the mirror. Remove the mirror for a week or so. Rearrange the perches and toys. Rotate the selection of toys to keep her environment "fresh". Regurgitation is a normal behavior but can affect health if she does it constantly.

This may be mating or sexual behavior. The whole seed indicates regurgitation instead of vomiting. The rubbing of the perch is likely mounting behavior. It should pass. You can provide different toys or rearrange the cage to distract him, but there is no cause for concern as long as he is behaving normally otherwise.

Regurgitation can be a sign of affection/wanting to mate, and some birds may display this behavior toward people they are bonded with if they do not have a mate. It is best to discourage the behavior by either stopping interactions when it happens, or distracting with a favorite toy or treat instead. Puzzle toys or things that can be chewed on/groomed may help him get out some boredom or affection for the object instead.

Birds do not recognize themselves in the mirror, so this would explain the mating behavior of regurgitating. I know it looks somewhat concerning, but it is more of a behavioral thing and is not concerning from a medical standpoint. If she seems more hormonal (like she's displaying a lot of mating behaviors), then you should expect this to pass within a few weeks. Unfortunately, there is not much you can do to stop her from doing this at this time...you'll have to just wait for this phase to pass. If she doesn't seem to be keeping any food down or is continuing the behavior for longer than a month, then it's best to have a vet check her out. There are a few different infections and conditions that cause chronic regurgitation, so it would be good to rule these out as a cause.

Birds can regurgitate as a sign of affection and if she is attempting to build a nest or make a nest of blankets this could be the case. However, if she appears at all ill, or has other symptoms such as listless behavior, refusal to eat or drink, changes in stool habits, swollen crop, etc, in addition to the regurgitation, then a vet visit is best to rule out any health issues.

Birds can sometimes regurgitate as a sign of affection/interest in trying to mate with you, so this could be that Bella is very comfortable and bonded with you. If she is otherwise healthy, I wouldn't be too concerned, but you may want to try to discourage the behavior by changing your interactions some if she seems too attached. If you suspect she may be ill instead, a vet visit is best.

Have Sky examined by your veterinarian or an experienced avian vet to diagnose illness or injury. You can also move the cage away from direct sunlight and limit daylight hours using a cage cover. This may stop his mating behavior if that is what it is. Limit any interaction, such as beak wrestling, that may foster mating behavior as well.