Teal in a reflective mood
This drake Teal decided to indulge in a simultaneous wing and leg stretch after sitting motionless for some time. It was on a small island and the conditions were just right for a mirror reflection. Even though it was in bright sunshine the angle was wrong to catch the green iridescence in its speculum, which is Latin for mirror and is that shiny patch at the back of the wing. Exactly like the iridescence on a Hummingbird's throat, the speculum just looks black unless you catch it at the right angle. For interest this is the same Teal and you can see the speculum's iridescent green on the closed wing: www.flickr.com/photos/timmelling/52460114490/in/dateposted/
The colours on a duck's speculum (and a Hummingbird's throat) are not created by pigments like most coloured feathers. The beautiful green iridescence is formed by refraction of light through a microscopically thin transparent layer on the feathers. Light reflects off both the front and back of this layer and the light travels slower through the layer causing minute phase differences in the light which creates colours. Miniscule differences in the thickness of the layers create different colours. The same thing happens with a drop of oil on a puddle. Each rainbow colour is created by tiny differences in the thickness of the oil layer. But if you catch the bird at the wrong angle the colour disappears and the speculum just looks black like this. Incidentally the word iridescence comes from Iris, the personification of the rainbow in Greek mythology. That's why beautifully coloured things like eyes and flowers are named iris.
Teal in a reflective mood
This drake Teal decided to indulge in a simultaneous wing and leg stretch after sitting motionless for some time. It was on a small island and the conditions were just right for a mirror reflection. Even though it was in bright sunshine the angle was wrong to catch the green iridescence in its speculum, which is Latin for mirror and is that shiny patch at the back of the wing. Exactly like the iridescence on a Hummingbird's throat, the speculum just looks black unless you catch it at the right angle. For interest this is the same Teal and you can see the speculum's iridescent green on the closed wing: www.flickr.com/photos/timmelling/52460114490/in/dateposted/
The colours on a duck's speculum (and a Hummingbird's throat) are not created by pigments like most coloured feathers. The beautiful green iridescence is formed by refraction of light through a microscopically thin transparent layer on the feathers. Light reflects off both the front and back of this layer and the light travels slower through the layer causing minute phase differences in the light which creates colours. Miniscule differences in the thickness of the layers create different colours. The same thing happens with a drop of oil on a puddle. Each rainbow colour is created by tiny differences in the thickness of the oil layer. But if you catch the bird at the wrong angle the colour disappears and the speculum just looks black like this. Incidentally the word iridescence comes from Iris, the personification of the rainbow in Greek mythology. That's why beautifully coloured things like eyes and flowers are named iris.