Tinbergen Observed a Seemingly Nonadaptive Behavior in Black-Headed Gulls (Larus

Tinbergen observed a seemingly nonadaptive behavior in black-headed gulls (Larus ridibundus) , i.e., that the gull parent does not immediately remove broken eggshells from the nest. Further observations revealed that

A) delaying shell removal reduced predation on still wet chicks by cannibalisitic neighbor gulls.
B) shell removal is only one behavioral option in an evolutionarily stable strategy.
C) the behavior is really neutral in its overall effect and only appeared maladaptive at first.
D) the behavior truly is nonadaptive, most likely the result of a pleiotropic effect.