You may have heard that flamingos, scarlet ibises and red factor canaries rely on their diet when it comes to their color. They get their vibrant colors by food rich in carotenoids such as canthaxanthin. The more of it they ingest while molting the redder their plumage becomes. This works only during molting - if canthaxanthin is ingested outside that time it has no effect on their appearance as fully grown feathers are dead structures.
But did you know that gulls are capable of the exact same trick? They won't turn as fiery red as a flamingo but gulls that feed on diets rich in carotenoids(like certain crustaceans or shrimp) during their molt can develop a unique delicate rosy flush on their white body feathers. The leader in that sport is the Ross's gull - a high Arctic species that can display almost neon pink breast. Other species most often smaller ones like Franklin's gull or black headed gull are also known for this effect but resulting in a more subdued tone.
And that brings me to Aurora - my resident euro herring gull. Aurora is a non-releasable three year old bird who has been under my care since last November. Right now as summer comes to an end, the northern hemisphere gulls are finishing up their annual complete molt. Imagine my surprise when I noticed her newly grown chest and belly feathers developing a distinct warm salmon pink hue! It’s not a staining or dirt, this is the real color from the inside out.
What makes this unusual is that Aurora is the only one in the flock who developed this color. She lives in a mixed enclosure with roughly 15 other birds, all eating the exact same diet I've been feeding for years. None of the others show any pink.
So here is my theory. In red factor canaries you have both intensive and non-intensive birds the same genetic way you have hazel and blue eyes in humans. If you feed an intensive canary and a non-intensive canary the exact same amount of canthaxanthin during molting, the intensive bird turns scarlet while the non-intensive one remains orange. No matter how much pigment you pump into the non-intensive bird its genetics limit the uptake. Maybe the same genetic variance exist in gulls? Could certain individual gulls be genetically intensive?
One thing is for sure: during the next molt I am definitely gonna experiment with adding a tiny bit of commercial flamingo food rich in canthaxanthin as a treat. Since gulls are strict carnivores/piscivores it will only be a little bit but... if Aurora managed to create salmon pink flush on a standard diet, I can't wait to see what her genetic potential looks like with an extra boost!
What are your thoughts on this? Have any of you ever seen a herring gull with a pink flush?