Hummingbirds lead very energetically expensive lives. Not only does their rapid wing beat of up to seventy-five times a second suck up calories; so do their high-speed chases of rivals and their diving, waggling, zigzagging shuttle flights to attract mates. To fuel their air derbies, they have to harvest hundreds of flowers per day; they don’t want to waste a dime visiting blossoms they’ve already sucked dry. So they keep track. And they do it, apparently, not on the basis of color or shape or other visual tips offered by the flowers themselves, but rather through spatial cues, as food-storing
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