Birds often display a distinctive patch, called a speculum, on their secondary wing feathers. The speculum comes in various colors among different duck species:
- Common teal and green-winged teal have iridescent green speculums edged with buff.
- Blue-winged teals showcase iridescent green speculums, while their name reflects the sky-blue wing coverts.
- Crested ducks and bronze-winged ducks exhibit iridescent purple-bronze speculums edged with white.
- Pacific black ducks display iridescent green speculums edged with light buff.
- Mallards showcase iridescent purple-blue speculums with white edges.
- American black ducks have iridescent violet speculums bordered in black, possibly with a thin white trailing edge.
- Northern pintails exhibit iridescent green speculums in males and brown in females, both with white trailing edges.
- Gadwalls feature white inner secondaries in both sexes.
- Yellow-billed ducks’ speculums are iridescent green or blue, bordered in white.
Additionally, other bird species, like certain parrots in the Amazona genus, also exhibit bright wing speculums in red or orange, although these colors are pigmentary and not iridescent.
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