When Curator Mollie walked by with Aldo on her glove, a flash of white caught my eye. The tip of the kestrel's tail was brighter than I had ever noticed. These new tail feathers, or rectrices, had just finished growing and were refreshingly crisp and clean.
Throughout the year, the tail becomes worn. A white tip on each feather stains quickly to a drab hue. The lack of pigment in these white tips also makes them more fragile than colored parts of the feather. That means the tip starts to break or fray more easily.
Many birds have feathers with white tips like the kestrel's tail. It may seem counterintuitive to have strong flight feathers with weakened edges that become damaged easily. But one hypothesis proposes that they serve as important signals to potential mates. If a female kestrel spots a male with a dull-tipped tail (maybe all of the white is worn away), she might infer that he has a pretty rough life and may not be able to take care of himself and a nest full of chicks. But when another male flies by, this time flashing a bright tail edge, she might assume that he has a good territory - and good genes - that keep him out of trouble.
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