Chapter 35, Problem 9TYK

Crows break the shells of certain molluscs before eating them by dropping them onto rocks. Hypothesizing that crows drop the molluscs from a height that gives the most food for the least effort (optimal foraging), a researcher dropped shells from different heights and counted the drops it took to break them.

Height of Drop (m)	Average Number of Drops Required to Break Shell	Total Flight Height (Number of Drops × Height Per Drop)
2	55	110
3	13	39
5	6	30
7	5	35
15	4	60

Data from R. Zach, Shell dropping: Decision-making and optimal foraging in northwestern crows, Behaviour 68: 106–17 (1979).

a. The researcher measured the average drop height for crows and found that it was 5.23 m. Does this support the researcher’s hypothesis? Explain.

b. Describe an experiment to determine whether this feeding behavior of crows is learned or innate.