Final answer:
The provided information does not explicitly point out which section describes Christian Rutz's method for finding a second species of tool-using crows and ravens.
Step-by-step explanation:
The section that describes how ecologist Christian Rutz narrows his search for a second species of crows and ravens that uses tools is not explicitly provided in the reference information given. Since no specific sections with the titles provided are mentioned in relation to Christian Rutz's work, we cannot accurately determine which section pertains to his method of narrowing the search for a tool-using species of crows and ravens.