Bright Colors For a Drab Day

Windy and cooler today, so here's a couple of zoo shots:

Golden-breasted Starling (Lamprotornis regius)
Lincoln Park Zoo, Cook Co, IL  9/30/2012

This is a Golden-breasted Starling (Lamprotornis regius) from the Lincoln Park Zoo.

Emerald Starling (Lamprotornis iris)
Lincoln Park Zoo, Cook Co, IL  9/30/2012

This one's an Emerald Starling (L. iris), again from Lincoln Park. The brilliant greens and purples we see here are the result of iridescence, not pigment. The barbs on the feathers are structured such that certain wavelengths are reflected back while others are transmitted farther into the feather, where they are absorbed by a layer of melanin. In some species, this works at any angles (think Blue Jays), but in iridescent species like this, the apparent color varies with the angle that the feather makes with the light.

This structural coloration is responsible for all of the blue colors that we see in birds. Green colors in most birds come from either iridescence, as here, or as a structural blue mixed with a yellow carotenoid pigment.

But here's a green bird that doesn't depend upon structural color at all:

 Livingston's Turaco (Tauraco livingstonii),
Milwaukee County Zoo, WI 6/5/2006

This is a Livingston's Turaco (Tauraco livingstonii), taken at the Milwaukee County Zoo. The green you see here is actually due to pigment, specifically to turacoverdin, a group of porphyrin pigments once thought to be unique to turacos.

Here's another turaco:

 Violaceous Turaco (Musophaga violacea),
Milwaukee County Zoo, WI 6/5/2006

This is a Violaceous Turaco (Musophaga violacea), again from the Milwaukee County Zoo. (Both of these turacos, and indeed all turacos, are native to Africa.) I can't find any source discussing the blue color you see here, so I assume it's due to structure. This color, though, isn't:

 Violaceous Turaco (Musophaga violacea),
Milwaukee County Zoo, WI 6/5/2006

The red you see on this guy's wing is due to turacin, another porphyrin unique to this group.

Pigments very similar to turacoverdins have recently been found in Galliformes, leading some researchers to suggest that turacos evolved from Galliformes. (1) On the other hand, another very similar pigment has been found in jacanas, members of the Charadriiformes, which suggests to me that evolving these pigments may be easy enough to make their presence a bit chancy as an indicator of phylogeny.

(1) Dyck, Jan (January 1992). "Reflectance spectra of plumage areas colored by green feather pigments". The Auk. 109(2): 293–301.