Black-chinned Hummingbird Archilochus alexandri Credit: Jack Lizard
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Hummingbirds stand out from other birds due to their colourful plumage, especially on the crest, throat and rectrices (tail). Males of the species that frequent open areas are usually more brightly coloured than those that live in forested environments. Colours are a valuable clue in the identification of species.
Iridescence
The best way to observe hummingbirds is to place yourself with your back to the sun. Depending on the angle of the light hitting their feathers, they will seem to shimmer when they face you, but appear dark and lacklustre when the birds turn around. This effect, called iridescence, is the same one observed with soap bubbles or oil lying in a thin layer on the surface of water. Colouration is usually linked to pigmentation. Iridescence is a physical phenomenon caused by platelets distributed in a more or less homogeneous manner in the feather barbules of hummingbirds.