There are a few things to look for when trying to determine if a baby rabbit has been abandoned. If the baby rabbit is cold, wet, or not breathing, then it is definitely in need of help and should be brought to a veterinarian or animal shelter immediately. However, if the baby rabbit is warm, dry, and seems to be breathing normally, then it may not need assistance. In this case, it is best to watch the bunny for a while and see if its mother comes back. You can also try calling around to local wildlife rehabilitators to see if they can take care of the bunny. If you decide to care for the baby rabbit yourself, there are a few you will need to do in order to make sure that the baby bunny stays healthy. You will need to make sure that the baby bunny is warm, fed, and hydrated. If you are caring for a very young rabbit, it is especially important to keep them warm because their body heat can drop quite quickly. It is also helpful to have an "incubator" if possible so that you don't have to worry about your own body heat potentially harming the baby bunny. In conclusion, there are a few key things to look for when determining if a baby rabbit has been abandoned by its mother. When in doubt, it's best to bring the animal into care or contact your local wildlife rehabilitator as soon as possible.