One possible explanation for why some birds migrate and others
maintain year-round residency in a single location is intelligence.
Specifically, birds with small brains, relative to their body size,
are simply not smart enough to find food during the winter and must
migrate to warmer climates where food is easily available (Sol,
Lefebvre, & Rodriguez-Teijeiro, 2005). Birds with bigger
brains, on the other hand, are more creative and can find food even
when the weather turns harsh. Following are hypothetical...