The most credible explanation for the higher rate of survival of the large birds is:
The large birds may be the hardest for predators to attack.
This reasoning aligns with the observed data that the large birds are less likely to be killed by predators. Their size could make it more difficult for predators to catch them, as larger prey can be more challenging to handle, and they may also be able to defend themselves more effectively against attacks. The other options do not provide strong reasoning for the observed survival advantage.