Outside My Window

Northern cardinals in May and February (photos by Cris Hamilton)

Why do birds look fat in winter and thin in the summer?  Have they lost weight?

No.  They're trying to stay cool.

Underneath their smooth outer feathers birds wear down coats all year long.  The down keeps them especially warm when they fluff it out to hold more heat next to the skin.  This fluffing makes them look fat on cold winter days.

When it's hot, they can't take off their down coats so they force hot air out of the down by compressing their outer feathers.  This makes them look thin.

The cardinal on the left, above, is not the thinnest one I've ever seen.  Cris Hamilton took his picture in May when the temperature was pleasant.  He'll look considerably thinner this month.

It's just another way that birds cope with heat.

p.s. We think of down as white but on a northern cardinal it's black.  Click here to see a northern cardinal's body feather, called a semi-plume, black at the root and red at the tip.

(photos by Cris Hamilton)

Song sparrow singing (photo by Peter Bell)

How do birds cope with heat?  They have several obvious ways and at least one we can't see.

Like us, birds stand in the shade and bathe to cool off.  They also appear to pant -- actually gular fluttering -- but their hidden cooling method is a surprise. They use the nasal conchae (pronounced KONK eye) inside their beaks.

Nasal conchae are complex structures that moderate the temperature of inhaled air and reclaim water from exhaled air.  Birds that live in hot dry places would benefit from bigger, better conchae.

A study published in The Auk: Ornithological Advances in 2016 found just that.

Raymond Danner of UNC Wilmington and his colleagues used CT scans to display the internal beak structures of two subspecies of song sparrows. The specimens were collected in Delaware and Washington, DC.

Delaware and D.C. don't seem to have different climates, but a bird of the dunes copes with a hot dry micro-climate compared to one that nests in a wooded inland park.

Indeed, as reported in Science Daily, the CT scans showed that "the conchae of the dune-dwelling sparrows had a larger surface area and were situated farther out in the bill than those of their inland relatives."

Here's a dune-dwelling song sparrow beak with elaborate air conditioning structures.

CT scan shows nasal conchae inside the bill of a Song Sparrow (photo credit: E. Gulson-Castillo and E. Sibbald via Science Daily)

This extra internal gear means the dune-based song sparrows (Melospiza melodia atlantica) have larger beaks than their inland cousins.

I'll admit I haven't noticed the slightly larger beaks of the beach birds.  Have you?

(photo by Peter Bell)

Multiple wingtips vortices roll off the tips of a flying jackdaw's wings (photo linked from viaScience Daily, credit: Aron Hejdström)

It doesn't make sense but if your wings are the right shape flapping saves energy.

Birds and airplanes must constantly overcome drag to stay aloft. One source of induced drag occurs during lift when swirls of air, called vortices, roll off the wingtips.  This small plane generates a huge wingtip vortex, forcing it to burn more fuel as it flies.

Wingtip vortex from an airplane (photo from NASA in the public domain on Wikimedia Commons)

Large soaring birds, such as turkey vultures, reduce drag in two ways. Their wingtip feathers form slots that break the single vortex into smaller ones (small is good!), and they turn their wingtips up as they soar.

Turkey vulture (photo by Chuck Tague)

Southwest Airlines turns up its wingtips, too, to save fuel.

Wingtip turned up to reduce wingtip vortex (photo from Wikimedia Commons)

But what about smaller birds that flap all the time?  Are they doomed to inefficient, labor-intensive flight?  A new study from Sweden says no.

Biologists at Lund University studied jackdaws (Corvus monedula), a corvid smaller than the American crow. Using mist and multiple cameras they found that the birds' slotted feathers, specifically designed for flapping flight, also break up the vortex into multiple swirls.  See them rolling off the wings in the study photo at top.

Now that we know slots are efficient for both flapping and soaring, what prompted their development? The study's authors "propose the hypothesis that slotted wings evolved initially to improve performance in powered (i.e. flapping) flight."

In fact, flapping saves so much energy that author Anders Hedenström suggests, "We could potentially build more efficient drones to fly with active wingbeats. Within a ten-year period, we could see drones which have the morphology of a jackdaw."

Read more about the study at Science Daily or the original paper here at The Royal Society.

(photo by Aron Hejdström linked from Science Daily)

Dark-eyed juncos in scent study (photo courtesy of BEACON)

True or False?

Birds have little or no sense of smell.  ... False!

Turkey vultures, seabirds, kiwis and parrots are known for their sense of smell.  And every time I turn around a new study finds more species with olfactory prowess.  As Audubon Magazine says, "In fact, every bird tested has passed the sniff test."

Back in 2011 Danielle Whittaker showed that the scent in preen oil varies among dark-eyed juncos. Those who smell the best, from a junco's point of view, attract more mates.  Yes, dark-eyed juncos can smell.

Read more in this vintage article: They Use Cologne

(Photo: courtesy of BEACON via Science Daily)

Barn owls, western Pennsylvania, July 2017 (photo by Anthony Bruno)

Birds hear really well -- especially barn owls -- but where are their ears?

This vintage article from July 2010 reveals where they are in Anatomy: Under The Feathers.

p.s. Did you know barn owls' ears are lopsided?
Their left ear is opening higher than their right one!  Learn more in A Ranger's Random Walks blog post from November 2014.

(photo of barn owls, July 2017, by Anthony Bruno)

Recently molted feathers of a black-legged kittiwake (photo by Jymm in public domain on Wikimedia)

On Throw Back Thursday:

Many birds molt during summer's "down time" between raising their young and fall migration.  At this point their feathers have worn out.

However (news to me!) female peregrine falcons choose a different time of year.  They begin to molt during incubation, a convenient time to do it because they're temporarily sedentary and their mates supply their food.  That's why we sometimes see a peregrine primary feather in the nest box.  Who knew!

Read more about feather wear and molting in this vintage article: Feathers Wear Out

(photo from Wikimedia, in the public domain.  Click on the photo to see the original)

Dori rolls the eggs before she resumes incubation (photo from the National Aviary falconcam at Gulf Tower)

To become baby birds, eggs must be warmed to around 98.6 °F and remain at that temperature while the embryos develop.  Adult birds that incubate(*) have special equipment to accomplish this:  bare skin on the belly called a brood patch.

We don't usually see the brood patch because surrounding feathers close over it to keep the adult warm.  When a bird comes back to its nest to incubate, it opens its belly feathers to lay its bare skin against the eggs.  You may have seen peregrines open their belly feathers by standing over the eggs and rocking side to side.

Click on the link below to see an American kestrel's brood patch and learn about this important part of bird anatomy, the Brood Patch.

(*) p.s. In eagles and peregrines, both sexes incubate so both have brood patches but this isn't the case with all birds.  In many duck species, only the female incubates so the males don't have brood patches.

(photo from the National Aviary falconcam at Gulf Tower)

Great horned owl blinking its thrid eyelid (photo by Chuck Tague)

Did you know that birds have three eyelids?

Did you know they can see through the third eyelid, at least a little, because it's transparent or translucent?

Read more about this fascinating and useful part of bird anatomy in this vintage article from 2010 about the Nictitating Membrane

(photo by Chuck Tague)

Black and yellow birds who flock together in Western Panama (photo composite)

On Throw Back Thursday:

These birds are wearing black-n-gold!

Just before the Steelers AFC Championship game in 2011 I explained why these black and yellow species tend to flock together.

This Sunday the Steelers are again in the AFC Championship.  What better time to revisit birds wearing black-n-gold.  Read on!

Wearing Black 'N' Gold

(composite photo credits, top left to right, then bottom left to right:
1. Slate-throated Whitestart: Corey Finger on 10000birds.com
2. Sooty-capped Bush Tanager: Wikipedia
3. Yellow-thighed Finch: Wikimedia Commons
4. Collared Whitestart: Jan Axel on janbirdingblog.blogspot.com
5. Silver-throated Tanager: Kent Fiala’s Website
6. Yellow-throated Brush Finch: Atrevido1 at Solo Aves on Flickr)

Hollow bone (photo from Henderson State Univ Nature Trivia by Renn Tumlison)

On Throw Back Thursday:

Six years ago I ran a series on bird anatomy.  Here's a refresher course on bird bones, the strong, hollow, lightweight structures that allow them to fly:  Anatomy: Hollow Bones