How Melanin Helps Seagulls Soar
Melanin is a surprisingly versatile protein. We know it’s used as a pigment in birds to produce black, grey and earth tones. But in this episode we’ll see one of its much less obvious benefits: helping seagulls fly.
EPISODE NOTES
Expanding on the idea that colouration evolves with periods of activity, nocturnal birds of prey also tend to have duller colours - along with less sophisticated colour vision. Owls are dichromats, sacrificing a broad colour spectrum for much better night vision.
Another hilarious trade-off owls make (which may end up as its own episode someday) is to be dumber for the sake of that night vision. Their huge eyes, evolved to capture as much ambient light as they can in nocturnal conditions, actually limit the amount of space their brains can take up in their skulls and make them among the dumbest birds of prey. Extra funny given that we’ve made owls symbols of intelligence and wisdom.
TRANSCRIPT
Last time, we looked at how birds produce their incredible range of colours. Now we’re going to explore some of the reasons why.
Colourful birds tend to have something in common: they’re diurnal, active during the day. And that simple fact led to an evolutionary snowball. To take advantage of all that sunlight, they develop sophisticated colour vision. Many birds are tetrachromats - they have four types of colour-sensing cells in their eyes, while we only have three. It gives those birds a wider spectrum of vision and drives the evolution of more dramatic colouration.
For a counterexample just look at mammals. They’re frequently nocturnal or crepuscular - active in periods of low light. So they end up with mostly dichromacy, only two kinds of colour sensing cells. And compared with birds they tend to look downright dull.
For those diurnal birds, pattern and colour are essential parts of identification and courtship. To the point where I think we can sometimes assume any colour or pattern has to do with display.
But those pigments and patterns can also evolve for totally different reasons: camouflage, thermal regulation, some even weirder. So for just one example, let’s look at gulls.
There are 23 species in Canada. They’re ‘soaring birds’, they can stay aloft without flapping their wings by taking advantage of air currents and gliding. Gulls are specifically ‘active soarers’ - they can soar, but flap more often than say, an osprey or vulture. Regardless, they need to stay in the air a long time when hunting over water.
And across 23 species, a pattern starts to emerge. White bodies. Darker wings. Black wingtips. That kind of parallel evolution usually points to a strong advantage, but what is it?
Let’s start with those black wingtips. As we learned last time, melanin is the pigment responsible for black, grey and earth tones. But it does a lot more for birds. Especially these birds.
Melanin granules in the feathers make them stronger and stiffer. It makes them resistant to physical degradation and damage from UV radiation. In other words, it makes them perfect as the tips of the sturdy primary feathers that take the brunt of stress when flying.
So that explains the black wingtips. But there’s an even cooler reason for the rest of the gull’s colouration. Or rather, warmer.
Melanin absorbs almost all light, which also means absorbing a lot of heat. Darker feathers will warm up more than lighter ones. And researchers wondered if that heat absorption had anything to do with this common pattern in gulls.
Their studies showed that the darker feathers heated up, as expected - but more important, they heated the air around and flowing through them. Hotter air is less dense and and flows more freely, which reduces drag. This pattern on gulls can actually improve their flight efficiency by 20%
but then if hotter air makes for more efficient flying, why aren’t all gulls jet black? One reason may be an even more subtle effect. Lighter feathers near their bodies and darker feathers out toward the tip of the wing create a natural temperature differential. There can be a nine degree difference between white and black feathers. Why does that matter? Because that difference can actually produce a convection current over the wing, increasing air flow and lift.
So that signature gull look is invisibly exploiting a lot of subtle physical properties to help them stay aloft longer and more easily. Just one example of pattern and colour going so much further than simple display.
And next time, we’re going to take a look at another species who has taken full advantage of that endlessly useful protein, melanin.