Q: There is a dead baby bird in the nestbox – should I remove it?
A: Yes, although the parents may take it out themselves.
Sometimes a nestling dies. Although you may never know what happened, see Predator & Problem ID & Solutions for possible reasons. If the baby is small enough, one of parents may remove the body. I recently saw a nestcam video of an adult even taking out a 9 day old baby (which involved considerable effort.)
If the parents do NOT remove it, you should. Otherwise it will start decomposing, get full of maggots etc., and could cause the other young in the nest to fledge prematurely.
If all the nestlings die, remove the bodies and the nest and clean out the box so it is available for a fresh start.
MORE INFORMATION:
Nature is not cruel, only pitilessly indifferent. This is one of the hardest lessons for humans to learn. We cannot admit that things might be neither good nor evil, neither cruel nor kind, but simply callous—indifferent to all suffering, lacking all purpose.
― River Out of Eden: A Darwinian View of Life
