Gouldian finches (Erythrura gouldiae) are colorful Australian seed-eating birds that nest in tree holes in the wild or in nest boxes when bred in captivity. Their nests are always dark inside so the nestlings have unusual mouth markings to attract their parents’ attention. Each nestling has:
Four opalescent tubercles at the corners of the gape that reflect a bluish light.
Patterns inside the mouth that guide toward the gullet.
To further attract attention, the nestlings hold up their mouths and rotate their heads as shown in this video of 3-day-old chicks.
The nestlings’ elaborate show may have evolved because …
Gouldians are among the most difficult finches to breed successfully because they are not wonderful parents and have a tendency to abandon both eggs and babies, or even refuse to nest at all. People who raise Gouldians usually keep society finches as well to serve as foster parents for eggs and babies. Societies are marvelous parents and will be happy to foster other species.
Both studies correlated the annual mean summer temperature of the species’ breeding range and reached the same conclusion: As the climate heats up, birds are getting smaller.
We should expect this.
There’s a biological rule of thumb called Bergmann’s Rule which states that, within a species, populations living in colder climates have larger body size than those in warmer climates. Bergmann’s explanation is that large animals have a lower surface-area-to-volume ratio so they lose heat more slowly in cold climates while small animals have a higher surface-to-volume ratio and can cool off faster when it’s hot.
Song sparrows (Melospiza melodia) provide a good example of Bergmann’s rule because they range across North America from Alaska to Newfoundland and south to Mexico. I saw their variability up close in the Carnegie Museum of Natural History’s Section of Birds in December 2016. My photo below shows sparrows collected in Alaska in the top row, sparrows from Pennsylvania on the bottom.
Here’s a closeup placed side by side (below):
On the left, two song sparrows collected in Pennsylvania: Pittsburgh (leftmost) and Geneva Marsh.
On the right, song sparrows collected in Alaska’s Aleutian Islands at Unalaska (leftmost) and Sanak.
Alaskan song sparrows are so large that they have to be placed sideways in the tray!
Smaller size is normal where it’s warmer.
It isn’t bad news for birds and it tells us two additional things:
Birds’ bodies have been registering climate change long before we humans noticed or admitted it.
Photos are what you really need anyway. Include an object near the feather to give it a sense of scale (size). Remember the location and habitat where you found it so you know what species are possible. Now you’re ready to figure out whose feather it is.
First determine the feather type so you know where it came from on the bird’s body. At this point you don’t care about color.
Rectrix (tail): Tail feathers (plural:rectrices) have barbs of equal length on both sides of the vane. (red arrows)
Remige (wing): Wing feathers have short barbs on one side, long ones on the other. (yellow arrows short and long)
Contour feather: covers the body
Semiplume: insulation under the contour feathers
Down: the warmest insulation near the skin
Bristle: sensory vane near beak and eyes (unlikely to find)
Fitoplume: sensory vane on wings (unlikely to find)
Next, think of birds with colors and patterns at that location on the body.
For additional help use the U.S. Fish and Wildlife Feather Atlas ID Tool for North American birds. At the Feather Atlas you’ll need to know the feather’s size in centimeters before you begin.
Ready for a quiz?
A. The feathers shown above are from a great spotted woodpecker eaten by a predator in Germany. What body part did they come from?
B. Here are two feathers of North American backyard birds. It’s a little harder to tell what body part they came from. (Length: red=9-10cm, blue=12-14cm) What do you think? Can you identify the species?
It’s challenging to identify feathers. Here are more resources to help.
Long-tailed ducks, common eiders and surf scoters eat crustaceans and mollusks that they pull from the ocean floor. Their populations are in steep decline, in part because hundreds of thousands of them die as bycatch in gillnets.
Federal fishing laws solved the bycatch problem for dolphins and whales by requiring pingers to warn the mammals away. Fish can’t hear the pingers but dolphins can. Is there a sound that will work for ducks?
University of Delaware grad student Kate McGrew tested long-tailed ducks, common eiders and surf scoters and found out they can hear 1-3 kHz underwater.
Fish cannot hear above 2 kHz so there’s hope for the ducks.
This New York Times ScienceTake video shows how McGew trained the ducks.
We usually see American robins (Turdus migratorius) with their wings closed. They perch in a tree, sit on a nest, or walk with their classic 3-steps-and-stop gait. Even in flight robins close their wings, flapping and gliding in a pattern similar to their walk.
This view of a robin with open wings reveals a surprise. The robin’s armpits, called axillaries, match its belly.
A study at the University of Ghent determined that the black-and-white color combination generates extra lift because of the temperature difference between the colors.
Using taxidermied wings, a heat lamp and a wind tunnel, the researchers measured airflow over the wings in a variety of wind conditions. They found that:
… dark feathers grew hotter than lighter colored feathers and they also gained heat faster than lighter colors. The researchers found temperature differences as great as nine degrees between black and white feathers on the same wings—enough to create a convection current in the air just over the wing, moving from the bird’s body outward along the wing.
Most owl species have camouflage-colored bellies, but most barn owls (Tyto alba) do not. Though their backs blend into their surroundings, the majority have brilliant white faces, bellies, underwings and legs. The rest are better camouflaged in rusty red, below.
The white color stands out in moonlight but is this visibility a disadvantage? Does the white owl’s prey see it coming and escape? Are reddish owls more successful on moonlit nights? Researchers ran tests to find out.
In a barn owl study in Switzerland, scientists have been tracking plumage, prey availability, moon phases and breeding success for over 20 years. When they correlated moon phase with hunting success, they found that reddish barn owls have lower success on full moon nights than white ones.
This seemed very odd so they set up an experiment with full moon lighting and two taxidermied owls posed in flight — one white, one reddish. When a vole was placed in the “moonlit” room and presented with a flying (stuffed) owl, it froze in place for an extra 5 seconds when it saw the white one. Those 5 seconds were just enough time for the white owl to pounce. The reddish owl was out of luck. Apparently the glowing white plumage has its advantages.
For centuries scientists have assumed that hummingbird beaks are always shaped for the flowers they feed on, but a recent study of their nectar-feeding mechanisms produced a surprising result. Some male hummingbirds have beaks that are inefficient for feeding but great for fighting.
Alejandro Rico-Guevara, an evolutionary biologist at UC Berkeley, assembled a team to study the biomechanics of nectar drinking. Using high-speed cameras they watched the entire feeding apparatus including bill shape, tongue shape, fluid trapping and elastic pumping.
Surprisingly, they found that male beak shapes in several South American species make it harder for males to draw in nectar. The females have nectar beaks but the males have straight dagger beaks or backwards facing teeth and hooked tips. You can see some of these features on the male tooth-billed hummingbird (Androdon aequatorialis) below.
There are many cool things about Atlantic puffins (Fratercula arctica). Here are two things that might come as a surprise.
(1) When Atlantic puffins fly back to their nests to feed their hungry chicks they need to carry as many fish as possible. How do they clamp them in their beaks? They press their spiny tongues on the fish to hold them against the roof of the mouth.
(B) We think puffins’ beaks are beautiful but we’re seeing only half of it. Where we see yellowish stripes the puffins see glowing ultraviolet. Read more about their colorful beaks in this article from Audubon.org.