Crows are small, agile fliers compared to larger, more unwieldy birds of prey. This means that crows often harry large predatory birds to drive them away from their nests. In this photo, a crow is doing just that--- but a photographer captured it at the perfect moment to make it look like the crow was riding on the eagle.

Speaking of nest defense, an interesting study from 1987 found that urban crows get used to human presence, while rural-dwelling crows still get nervous and defensive when humans are around. This is just one example of a single species adapting in real-time to human presence. City Crow, Country Crow, anyone?