There’s no mistaking the dizzying display of a hummingbird’s wings as it zips around from flower to flower looking for nectar. But often, that same frantic action is used to chase other hummingbirds.

Hummingbirds are zipping around San Diego County’s backyard gardens, scrub-covered coastal hillsides, and the warming Anza-Borrego Desert. Seasonal hummingbirds are making their way back to Southern ...