Invariably when someone tells me their lovebird killed its mate, the truth is that one bird of unknown sex killed another of unknown sex. 

In most instances, a cock bird has died and another bird has been introduced to mate with the widow. If the original nest box or any other box for that matter remains, the odds are against the newly introduced bird's survival. It shouldn't be too difficult to understand how this could happen. 

If a stranger entered your home uninvited and proceeded to take all your possessions, wouldn't you fight to protect your home and property? A lovebird is no different. Love at first sight is not, as the name suggests, the way it always happens. 

So when introducing a new mate to one of your trusted breeders, do so in a new environment unfamiliar to both birds and leave the nest boxes out for a couple of weeks. Then all should proceed in the normal way.  ©