Feathers are vital to a bird’s survival but they wear out and have to be replaced by molting. The best time to do this is when feathers are not urgently needed for migration, courtship or warmth. That makes summer the time to molt. Here are a few examples.
Ruby-throated hummingbirds (Archilochus colubris), above, have to look flashy at the start of the breeding season so they molt their body feathers from June to August. On the wintering grounds they molt flight feathers in preparation for their strenuous spring migration. Look closely at ruby-throats this summer and you’ll see that their body feathers are not as perfect as they were in May.
Northern cardinals (Cardinalis cardinalis) wrap up their last brood of the season in mid summer and begin to molt in mid July. By August they will look very ragged, male and female shown below. Some will be bald.
Male and female peregrine falcons (Falco peregrinus) molt at slightly different times. Females molt their primary wing feathers while they’re incubating eggs (March-May) because their mates are doing all the hard flying to provide food. The males molt their primaries in July after teaching the young to hunt.
Birds molt the same flight feather on each side of the body so that flight remains balanced. Morela’s wings look sleek while she’s sunbathing because she replaced her wing feathers a few months ago.
However she is molting her two central tail feathers. Click on the photo below for a highlighted version showing the two growing feathers.
Meanwhile Ecco is looking very ragged (below). I saw him flying yesterday with a feather obviously growing in on each wing.
Have you noticed that Canada geese (Branta canadensis) are not grazing in their usual upland haunts? They are staying near water because they cannot fly while they molt all their primary feathers at once.
On Sunday at Duck Hollow we saw a female mallard with odd plumage. She was paired with a male mallard but she resembled a male in eclipse plumage. Was this duck a hybrid? Or was it something else?
Michelle Kienholz was so intrigued that she took photos and sent them to the Duck ID group where she learned an amazing thing about female ducks. This odd mallard at Duck Hollow is an “intersex hen.” She is becoming male in a process called spontaneous sex reversal (SSR).
Female ducks are born with two ovaries but only one develops. The left ovary actively pumps out hormones to stifle the male genes, making the bird truly female. If a disease damages the only ovary and it stops producing hormones the female duck spontaneously turns into a male. Experiments have shown that the now-male duck is able to breed and fertilize eggs.
Because most ducks are sexually dimorphic a female with a dead ovary eventually looks male as well. The intersex hen at Duck Hollow is partway through her/his outward transformation, which is why she/he is in eclipse-like plumage.
Notice the clues in her/his feathers that indicate the transition:
tail feathers are black and curly white,
green feathers interspersed on head
breast is darkening (top photo)
color line between neck and breast is becoming white
For more information on bird sex chromosomes see Anatomy: W and Z. For photos of eclipse plumage see Mallards in Eclipse. And here is an article about spontaneous sex reversal in chickens, a problem for chicken farmers.
Despite recurring winter weather we are more than halfway to spring and the birds know it. As their bodies prepare for the breeding season they develop brighter feathers, skin and beaks. Here are two backyard birds who make this transformation. One turns redder, the other loses stars.
Northern cardinals (Cardinalis cardinalis) molt from July to October, changing out their old feathers for new. At first the male doesn’t look bright red because the very tips of his new feathers are actually gray. You can see the gray feather tips on his back in the photo below.
By mid-winter the gray tips wear off and the male cardinal becomes brilliant red for the breeding season.
Cardinals get their color from what they eat so diet plays a part and there are regional and habitat differences that affect the color. But no matter where they live, male cardinals turn redder in winter.
European starlings (Sturnus vulgaris) have a similar strategy for changing into breeding plumage. When their feathers are new in autumn each one is tipped with white so their bodies appear to be sprinkled with stars — hence the name “starling.” This close up shows that on new feathers the stars are tiny V’s on the feather tips.
Over the winter the white tips wear off, especially on their head and breast feathers. By the time it’s breeding season their faces and chests are shiny, sleek and iridescent. Starlings lose their stars in the spring.
There is one more transformation that starlings make that will tell you which are male and female.
In the winter starlings’ beaks are dark brown but turn bright yellow in spring. You can tell the difference between male and female by looking at the color at the base of their beaks — the part closest to their faces.
Just like the baby colors — girls are pink, boys are blue. You can see it with binoculars.
Here’s a side-by-side comparison. The blue on the male at left is easiest to see. The pink on the female at right is pale and takes more effort to figure out.
(Cardinal photo by Chuck Tague. Starling photos from Wikimedia Commons; click on the captions to see the originals)
These high gloss eggs look like ceramic but were actually laid by members of the Tinamou family, native to Central and South America.
Great tinamou egg
Elegant-crested tinamou egg
Thicket tinamou (Crypturellus cinnamomeus) egg
Tataupa tinamou egg
Tinamous are shy, secretive ground-dwelling birds that resemble chickens but are closely related to ostriches and emus. 46 species range in size from the 8’7″ small-billed tinamou (Crypturellus parvirostris) to the 16-19″ grey tinamou (Tinamus tao). No matter where they live, rainforest, savannah or shrubland, all of them lay shiny eggs in a nest on the ground.
One would think that shiny eggs would be easily found by predators, especially after researchers examined the cuticle, the egg’s outside layer, and found:
They quantified its smoothness down to the nanometer scale and measured the shininess of the mirrorlike surface, finding that tinamou eggs are up to 14 times as glossy as the average chicken egg. A spectroscopy test also revealed that the blue eggs were iridescent (the green and brown eggs were too shiny for the spectrometer to accurately measure).
White-throated sparrows are back for the winter. Here’s something to remember when you see them.
In the world of birds, the bright ones are male and the dull ones are female, right?
Not so for white-throated sparrows (Zonotrichia albicollis). In this species the bright white versus dull tan stripes are color morphs. The bright white-striped bird at top can be either male or female. The tan-striped below is also either sex.
The bird with bright yellow lores on the left could be female. The one with dull yellow could be male.
Amazingly the colors match up to personality traits regardless of sex.
White-striped birds are bold, aggressive, philandering and not particularly caring of their kids. They are not the best parents.
Tan-striped birds are gentle and very caring of their young. They’re the good parents among white-throated sparrows.
Since each bird can tell the other bird’s personality at a glance, you would think the gentle would mate with the gentle and the bold with the bold. But that’s not how they do it. They always mix it up.
White-striped (aggressive) males mate with tan-striped (care-giving) females and tan-striped (gentle) males mate with white-striped (philandering) females. Thus the color morphs and personalities persist.
We humans assume that what we see is what everyone else sees, including other species. But this isn’t so.
Peregrines see much finer details at a greater distance that we do. The details don’t blur for them in a 200 mph dive. (Click the link to learn more.)
Cats cannot see red-green nor distant details, but they see much better in the dark. Who needs distance vision while looking for a nearby mouse at night? Click here to see photos of our vision versus cats’. Notice the normal vs. red-green-color-blind examples below.
White-tailed deer see regular blaze orange as gray but if the orange has fluorescence it stands out for them. Their vision is best in the blue range so that they see well in twilight.
Birds see ultraviolet light though we cannot. Here’s how we know this and a hint at what birds look like in ultraviolet light.
Do other species see what we see?
No. Birds see more.
(peregrine photos by Chad+Chris Saladin, deer photo by Kate St. John, remaining photos from Wikimedia Commons)
There are probably several reasons why teeth disappeared but the main one is this: In order to fly well it’s important to reduce excess body weight. Bones and teeth are heavy so over time birds evolved hollow bones and toothless beaks. They compensate for the lack of teeth by chewing food in their gizzards.
They also compensated by using their beaks as multi-purpose tools to grasp, twist, pry, crack open shells, and sever tendons.
Each species developed a beak for its lifestyle. A few of them evolved beak modifications that resemble teeth.
Among tooth-billed hummingbirds (Androdon aequatorialis) the males have a “straight bill with a prominent hooked tip and backward-pointing tooth-like serrations on the distal half. The modification is absent on the female bill, and thus may be related to sexual selection,” describes Birds of the World. Perhaps the “teeth” are used for fighting.
The critically endangered tooth-billed pigeon (Didunculus strigirostris), the national bird of Samoa, has a stout curved bill with a specially toothed lower mandible.
[The bill] is adapted to feed on Wild Mahogany Dysoxylum spp. fruits, although first-year birds apparently cannot do so. These fruits have a tough capsule that it is able to open using its strong bill, removing the flesh using a sawing action with the lower mandible.