Mate desertion happens when an animal, usually birds or mammals, decides to leave their partner and mate with another individual. It's like when you decide to play with a new friend instead of your old friend.
Just like humans, animals have different reasons for mate desertion. Sometimes one partner gets sick or injured and can no longer help take care of the babies, so the other partner leaves to find a new mate who can help. Other times one partner finds a better mate with better traits, like being stronger or a better provider.
In the animal world, mate desertion is normal behavior and even necessary for the survival of the species. It helps to diversify the gene pool and ensure that the offspring are strong and healthy.
However, just like in human relationships, mate desertion can also be hurtful and can cause emotional pain for the partner left behind.