Despite not seeing a living one until a visit to the United States in 1857, Gould maintained a lifelong passion for hummingbirds. Between 1849 and 1861, he produced this beautiful work on the different species of hummingbird. The plumage of the tiny birds is iridescent, meaning that it reflects light, a feature that the illustrations in this series were able to replicate by adding gold leaf under transparent layers of oil paints and varnish.