What do tree swallows, starlings, pigeons, hummingbirds, and mallard ducks all have in common? Besides being birds, of course, each of these species sports iridescent feathers that glimmer and shine when the light hits them. While observing a pair of pesky starlings at my bird feeder one day, the gleam of their feathers caught my eye and caused me to wonder: Why do some birds have iridescent feathers while others do not? What causes iridescence, and how does it serve the birds who flaunt these feathers? …

This Field Note was written by Elizabeth Domenech. Would you be interested in writing one? Contact Allison De Jong, Field Notes editor, at adejong [at] montananaturalist [dot] org or 406.327.0405. Please visit the Field Notes website at the Montana Natural History Center for more information.