Sleek or Fluffy?

Thanks to their ability to individually control each of their feathers to help regulate their body temperature, birds are remarkably changeable in their appearance. When cold, a perched bird can hunch down and “fluff up,” effectively creating an insulating down coat for itself. If the same bird is too warm, it can stretch out and sleek down its feathers to release heat and help it keep cool.

This Ruby-throated Hummingbird picture for example, recently uploaded to the Wingscapes BirdCam Photo Gallery by Michael from Shorewood, Wisconsin, provides an excellent illustration of the “stretch and sleek” cooling technique.