Passage Summary: A scientist watched ravens and discovered that young birds team up to bully older couples off of carcasses so they don't starve.

Reasoning: Heinrich observed that juvenile ravens cooperate in large groups to drive territorial mated pairs away from food sources, explaining why they appear to 'recruit' others.

Analysis: This stimulus describes a scientific investigation into a specific behavior that initially seemed altruistic. The reasoning moves from an observation (ravens calling others to food) to a functional explanation (juveniles needing strength in numbers to displace territorial adults). When identifying the method of reasoning, focus on how the study provides a self-interested motivation for a behavior that previously looked like selfless sharing. You are looking for a description of a study that explains a phenomenon by identifying the specific benefit it provides to the participants.