Spring migration is here! Have you ever wondered how migrating birds find their way home over thousands of miles? It turns out that vision plays a huge role BUT old and new discoveries show that the view from a bird’s eye may be stranger than we can imagine. Or maybe we can.
If you were a fan of Star Trek: The Next Generation in the 80s and 90s, you may recall the character Geordi LaForge, who was blind. Geordi wore a special cybernetic visor that in his words, allowed him to “see much of the electromagnetic spectrum ranging from heat and infrared through radio waves, et cetera, et cetera, et cetera.”
During the occasional moments when viewers saw what Geordi “saw”, the image was barely recognizable. Here’s an example, in case you haven’t seen the show.
This image features another character from the series, Lt. Commander Data. The left side is what Data really looked like. The right side, where the character is in a slightly different pose, is how Geordi “saw” Data.
What does this have to do with how birds see? I’m about to tell you.
Bird Vision Is Weird, Part 1
Migrating birds, including passerines and many sea and shore birds, can see a lot that humans and other mammals just aren’t equipped to perceive. For starters, they not only have much sharper vision than us mammals, they can also see ultraviolet (UV) light.
It turns out that a lot of birds have markings that are especially prominent in UV light. These photos of a red winged parrot illustrate what I mean. In normal light, the blue spot on its back is just another splotch of color. Under ultraviolet light, that patch shows up brightly, meaning it would be extra-prominent to other birds. (Notice the similarity to Geordi’s view?)
Science is just beginning to figure out how the ability to see UV light is useful to birds. Mate selection is one likely way. For one thing, species in which males and females look exactly the same to us look distinctively different to each other when the feathers of one (usually the male) have UV-reflecting areas.
And in at least one species (blue grosbeaks), the male birds with the bluest, most UV-reflective feathers are also the best quality mates. They are the males that are healthiest, hold the largest territories and spend the most time helping to feed their young. (Does that sound like husband material or what??)
UV-sensitivity is also handy for finding food—many types of fruit and berries reflect UV light, as do quite a number of insects including certain butterflies, scorpions and flies. They probably attract birds like a lit-up drive-thru attracts us!
Going back to the parrot, it’s important to note that the UV photo doesn’t show how other birds would see it. That’s because the UV photo doesn’t include colors from the visible-to-humans spectrum that are also visible to birds.
Luckily, this short (narrated) video does a pretty good job of simulating what birds actually see when they look at each other.
The narrator seems most interested in the breast feathers. I think it’s interesting that the head is quite a bit brighter in UV light as well.
DO Try This At Home
If you have an Android device with a camera and want to have some fun, go to the Google Play Store and download ILab’s Animal Vision app. It lets you see and photograph the world as if you were viewing it through the eyes of any of several creatures—dogs, cats, birds and more.
The visualization may or may not be scientifically accurate, but it’s fun to try out.
Bird Vision Is Weird, Part 2
You probably already knew that birds can see UV light, but did you know that migratory birds can also see the earth’s magnetic field??? This extra dimension of their vision is called ‘magnetoreception’ and derives from the physical properties of a special protein molecule called Cry4, which is found in many bird organs including the retina of the eye.
Retinal Cry4 levels are higher during migration and scientists think the protein may just be the ‘secret sauce’ behind how birds migrate. Without getting too technical, the Cry4 molecule changes a bit depending on how the bird’s eye is positioned relative to the earth’s magnetic field, causing magnetic field lines to appear as areas of light and dark shade (and possibly some color) in the bird’s visual field.
The patterns of light and dark would appear at slightly different angles depending on which direction the bird is looking.
So what might that look like?
According to researchers in the University of Illinois Theoretical and Computational Biophysics group, a bird flying about 200 meters (650 feet) above the ground might see something like this (second row):
The squares in the top row are an isolated visualization of the magnetic field lines as a bird might see them when looking in the indicated compass directions. The second row combines the magnetic field view with the image a human eye would see.
What a bird actually sees would be the second row as it appears in ultraviolet light. (Sort of purplish, with brighter and darker spots of UV reflectivity. Like what Geordi sees.)
Can you picture that?
Consolation Prize for Humans?
Humans may not see UV light, but we can see the earth’s magnetic field sometimes. We call it the Northern Lights, a phenomenon that happens when charged particles from the sun strike atoms in Earth’s atmosphere.
Differences in color vision make passerines less conspicuous in the eyes of their predators
Expression patterns of cryptochrome genes in avian retina suggest involvement of Cry4 in light-dependent magnetoreception
Structurally based plumage coloration is an honest signal of quality in male blue grosbeaks
Double-Cone Localization and Seasonal Expression Pattern Suggest a Role in Magnetoreception for European Robin Cryptochrome 4
Ultraviolet vision in birds: the importance of transparent eye media
Scientists Identify Protein That Could Let Birds See Magnetic Fields
Robins can literally see magnetic fields, but only if their vision is sharp
Magnetic Compass of Birds Is Based on a Molecule with Optimal Directional Sensitivity
Retinal cryptochrome in a migratory passerine bird: a possible transducer for the avian magnetic compass