As far as birds go, the tiny, swift hummingbird is pretty in touch with color— they can see hues that we can’t imagine. Their feathers come in many shades as well, which is believed to help males find mates during courtship. Some females even use flashy feathers as a way to appear male to keep other birds from bothering them.
They can be purple like the Lucifer hummingbird (Calothorax lucifer), a bright turquoise like Rivoli’s hummingbird (Eugenes fulgens), and the appropriately named pink-throated brilliant hummingbird (Heliodoxa gularis) is pink. Biologists are still figuring out the role of these colors and how they appear in hummingbird feathers.
“I look out across the bird world for interesting colors and try to understand the physics of how those colors are being produced. With that knowledge, I could understand why some of these colors might be evolving more rapidly or why there might be more colorful species in certain areas of the world,” evolutionary biologist Chad Eliason from Chicago’s Field Museum tells PopSci.
However, when a team of scientists found a normally pink throated Heliodoxa hummingbird that had a gold throat instead, they thought it was a completely new species. DNA revealed something else– the gold-throated bird was a never-before-documented hybrid of two pink-throated species.
The team describes this unique bird that they first encountered during field work in the isolated Cordillera Azul National Park of central Peru in a study published February 28 in the journal Royal Society Open Science.
“I looked at the bird and said to myself, ‘This thing doesn’t look like anything else.’ My first thought was, it was a new species,” said John Bates, a curator of birds at Chicago’s Field Museum and study co-author, in a statement.
The team gathered more data using the museum’s DNA lab to confirm the surprise, and found that it matched one of the pink-throated hummingbirds local to the area, Heliodoxa branickii (H. branickii) in some markers. Still, most hummingbirds don’t vary this greatly within their own species,
The DNA sequencing looked at mitochondrial DNA–genetic material that is only passed down through the mother. The mitochondrial DNA provided a clear result that matched H. branickii.
When the team analyzed the bird’s nuclear DNA, which has contributions from both parents, it showed similarities to both H. branickii and a genetic cousin, Heliodoxa gularis (H. gularis).
However, the bird wasn’t half branickii and half gularis. One of its ancestors must have been half-and-half, and subsequent generations then mated with more branickii birds.
In order to answer the question of how two pink-throated bird species ended up producing a non-pink-throated hybrid, the team had to look at the complex ways in which iridescent feather colors are determined. Pigments like carotenoids (red and yellow) and melanin (black) give the feathers their base colors, but the structure of the feather’s cells and the way that the light bounces off of them produces structural color. The result is color-shifting iridescence in the feathers.
“We knew coming into this that [hummingbirds] had the most complex melanin structures or the iridescent structures of all birds,” says Eliason, who is also a co-author on the study.
An electron microscope examined the subcellular level of the throat feather structure and spectroscopy to measure how light bounces off the feathers to produce different colors. Subtle differences were found in the origin of the hummingbird parent’s colors, which may explain why hybrid offspring produced such a vastly different color.
“There’s more than one way to make magenta with iridescence,” Eliason said in a statement. “The parent species each have their own way of making magenta, which is, I think, why you can have this nonlinear or surprising outcome when you mix together those two recipes for producing a feather color.”
Sometimes hybrids are one-off occurrences or cannot reproduce like mules, but in other cases, they form new species. While it is not clear how common these kinds of hummingbird hybrids are, the team believes that they might contribute to the diversity of structural colors found across the hummingbird family tree.
They calculated that it would take six to 10 million years for this pink to gold color shift to evolve in a single species of bird, based on the speed of color evolution seen in hummingbirds.
On an evolutionary time scale, six to 10 million years is pretty fast, according to Eliason. Further study will help them understand how many generations it takes for these strange changes to occur and apply some newer genetics and genome sequencing tools to older studies on hummingbirds.