Lung capacity is increased. Exposure to bacteria is increased. Parents are able to identify the nest. Parents respond by giving more food.
I gave my students this multiple choice question: Scientists have observed that, even within the same nest, some young birds call louder than others. Which describes how a louder cry helps to ensure survival?

Only one answer is correct among these 4 choices:
- Lung capacity is increased.
- Exposure to bacteria is increased.
- Parents are able to identify the nest.
- Parents respond by giving more food.

Could you tell me which one is correct?

Parents respond by giving more food.