Begging is how a helpless nestling communicates hunger to a parent bird, and it usually combines sound, movement, and visual display to grab the parent's attention over that of its nest mates. Let's go through each listed behaviour and ask whether it fits this role.
- Playing dead: This behaviour, seen in some insects and reptiles, is used to avoid being detected or eaten by a predator, by looking lifeless. It is a survival tactic, completely unrelated to asking a parent for food, so it does not belong on the list of begging signals.
- Vocalisations: Chicks calling loudly and repeatedly when a parent returns to the nest is one of the most familiar begging signals in birds, and louder or more frequent calls often mean a hungrier chick.
- Fluttering of wings: Along with calling, chicks often flap their wings vigorously while begging. This visual and physical display reinforces the vocal signal and helps direct the parent's attention.
- Mouth gape and colouration: The bright interior of a chick's open mouth is a striking visual target that guides the parent exactly where to place food, and its size and colour intensity can reflect the chick's need.
So three of the four listed behaviours, calling, wing fluttering, and gape display, are genuine begging signals used in parent-offspring communication, while playing dead belongs to a completely different behavioural category.
Let's summarize:
- Bird begging combines vocal, physical, and visual signals aimed at the parent.
- Playing dead is an anti-predator tactic, not a food-solicitation signal.
Therefore, the correct options are (B), (C) and (D).