The contact call:

It's well known that lovebirds can make sounds that don't exactly please the ears. One sharp  sounding call is the so-called contact call. As the name indicates, the purpose of this call is to keep partners and young in touch, even when they move in groups to drinking and eating areas. It also keeps the flock together. If foreign lovebirds should enter a flock, members of the group recognize the outsiders immediately. If there is enough feed and if the young lovebirds have not yet formed definitive pairs and other conditions are favorable, new lovebirds aren't automatically rejected and may be considered as mates. If all pairs have been formed, however, chances are that outsiders will be rejected because they could disturb the peace of the group.

The alarm call:

Lovebirds have a so-called alarm call, which even humans can recognize as such. They use this call when danger is suspected or evident (lovebirds of prey or a dominant member of the group).

The fear call:

Even more piercing is the "fear call" with which you are commonly confronted if you take a lovebird that doesn't know you well into your hand. Lovebirds clearly find this stressful. They have this fear call even as nestlings, and you will hear it, for example, if you put a lovebird that fell from the nest back where it came from.

The contented twitter:

Nevertheless, you can note a peaceable, soft, relaxed twitter, especially in a quite noontime period, when the lovebirds actually seem to sing to themselves.