I speculate that this may a lot to do with protective activities related to the life-phase of their young, and a relatively programmatic ‘sense’ of what constitutes a commonly recognized threat. Adult crows in my neighborhood observed my feeding of their (relatively advanced) fledglings, but rarely took the food I offered. They did not swoop on me, but did appear skeptical. This is a slightly different environment (extremely urban) and their young were relatively independent by this time.