Category Archives: Bird Anatomy

Taking Out The Garbage

Western bluebird carrying fecal sac away from the nest (photo from Wikimedia Commons)

Nests look like safe havens for baby birds but if they’re not kept clean they can quickly become infested with pathogens and parasites, or their smell can attract predators. For songbirds it’s especially important to keep their nests clean. Fortunately their bodies have evolved to make this easy.

In the photo above, a western bluebird is taking out the garbage after visiting his nest. In his beak is a fecal sac, a package of white mucous membrane surrounding the feces of one of his nestlings. Every nestling produces a fecal sac shortly after eating. The packaging makes it easy to keep the nest clean.

What the parents do with the fecal sacs depends on the species. Most drop them far away from the nest but some species, such as American robins, consume the fecal sacs while the nestlings are quite young and carry the sacs away when the nestlings are older.

Just before songbirds fledge their bodies switch from producing fecal sacs to defecating wet feces over the edge of the nest. Robins’ nests don’t have whitewash beneath them until you can see the youngsters above the nest rim. By the time they are messy, baby robins are almost out of there.

Birds of prey aren’t as fastidious. If you watch peregrine and bald eagle nestcams, you’ll see two differences in their nest sanitation:

  1. Raptor nestlings don’t produce fecal sacs. Instead they back up to the edge and aim wet feces away from the nest.
  2. As the nestlings age the parents become lazy housekeepers, often leaving food debris at the nest as a self serve snack for the young.

Birds of prey aren’t worried that predators will smell their nests. That’s why they don’t always take out the garbage.

(photo from Wikimedia Commons; click on the caption to see the original)

Casting A Pellet

(Red-tailed hawk casts a pellet, photos by Chad+Chris Saladin)

Why does this red-tailed hawk throw up a long gray lump? Is he sick? Not at all. He’s casting a pellet.

Birds’ digestive systems are very different from ours, beginning with their beaks. Since birds don’t have teeth they swallow most of their food whole. The rest of their digestive system is geared to deal with this.

Birds have little saliva and few taste buds compared with mammals, which chew and physically process food as the first step and then subject it to chemical processing as the second step. Birds reverse this sequence. They start chemical digestion in the proventriculus [then the food] undergoes physical processing in the gizzard.

Ornithology, 3rd Edition by Frank B. Gill, page 164

We chew with our teeth and spit out the bones. Birds chew with their gizzards which then collect the bones, fur, and other indigestible bits into a lump. The bird spits out the lump when it’s a convenient size.

Owls, eagles, hawks and falcons cast pellets but so do many other birds “including grebes, herons, cormorants, gulls, terns, kingfishers, crows, jays, dippers, shrikes, swallows, and most shorebirds.” (quote from Wikipedia)

Scientists examine pellets to find out what the bird ate. One of the long-eared owl pellets below was dissected to reveal the rodent bones inside.

Pellets cast by a long-eared owl, dissected to show rodent bones (photo from Wikimedia Commons)

For whatever reason, it’s rare to see a bird casting a pellet so consider yourself lucky if you witness it, as Chad+Chris Saladin did in the photos above.

A NOTE ABOUT HANDLING OWL PELLETS from Wikipedia: Some rodent viruses and bacteria can survive the owls’ digestive system so wear gloves and sterilize the pellets in a microwave oven before handling. A 2005 study found outbreaks of salmonellosis at elementary schools associated with dissection of owl pellets: Smith KE, Anderson F, Medus C, Leano F, Adams J, 2005. Vector-Borne and Zoonotic Diseases,5, 133–136.

(red-tailed hawk photos by Chad+Chris Saladin; pellet photo from Wikimedia Commons; click on the captions to see the originals)

Too Hot!

Great blue heron gular fluttering (photo from Wikimedia Commons)

With highs over 90 degrees and dewpoints at 70 it’s just too hot in Pittsburgh! We’re coping by staying indoors with air conditioning but what do birds do?

This great blue heron in Florida is using at least five techniques for staying cool. 

  • He’s gular fluttering which looks like panting.  Herons are one of several kinds of birds that can vibrate the skin, muscles and bones of their throats to increase heat loss. See more here
  • He has wet belly feathers.  Aaahhhhh!
  • He’s exposing the skin on his legs to cool them off.
  • He’s holding his wings slightly open to cool off his “armpits” and
  • He’s standing in the shade.

He could also try soaring where it’s cooler or sleeking his body feathers to squeeze heat out of his downy undercoat.  (Maybe he’s doing the squeeze thing. I can’t tell.)

That’s all that most birds can do to cope with heat, but the ostrich has an additional amazing solution. 

When a body is warmer than the surrounding air it loses heat.  We know this happens in winter but the ostrich makes it work in summer.  He raises his body temperature in a controlled fashion —  4.2o C (7.5o F) during the day — so that his body loses heat to the outdoors. 

Male ostrich, bare legs (photo from Wikimedia Commons)

For us, it would be like having a fever on a hot day. 

No thanks! It’s too hot already!

(photos from Wikimedia Commons; click on the captions to see the originals)

Turning Green

Male scarlet tanager in August 2015 (photo by Tim Lenz via Flickr, Creative Commons license)
Male scarlet tanager on an ash tree, August 2015, Chemung County, NY (photo by Tim Lenz via Flickr, Creative Commons license)

Yesterday in Schenley Park I saw a scarlet tanager with blotches on his belly.  He was starting to turn green.

Scarlet tanagers (Piranga olivacea) molt twice a year.  In January through March they molt into breeding or “alternate” plumage while on their wintering grounds in South America. The females don’t change color but the males turn from green to scarlet. Young males often retain a bit of green (click here to see).

When the breeding season is over, they molt back to basic plumage in July through September. The males look blotchy at first but when they’re done they’re bright olive green with black wings as shown below.  By then they’re on their way to South America.
(photo at top in August, Tim Lenz; photo below in Oct, Andy Reago & Chrissy McClarren)

Scarlet tanager in October 2015 (photo by Andy Reago & Chrissy McClarren via Flickr, Creative Commons license)
Scarlet tanager in October 2015 (photo by Andy Reago & Chrissy McClarren via Flickr, Creative Commons license)

I was lucky to see yesterday’s scarlet tanager because he hardly made a sound.  Tanagers have stopped singing now that breeding is over.  This one was singing very softly.


p.s.  Did you know that female scarlet tanagers sing?  According to All About Birds: “The female Scarlet Tanager sings a song similar to the male’s, but softer, shorter, and less harsh. She sings in answer to the male’s song and while she is gathering nesting material.”

(photo credits: scarlet tanager turning green by Tim Lenz via Flickr, Creative Commons license; yellow-green scarlet tanager by Andy Reago & Chrissy McClarren via Flickr, Creative Commons license)

Where The Color Comes From

Indigo bunting (photo by Marcy Cunkelman, May 2015)
Indigo bunting (photo by Marcy Cunkelman, May 2015)

Why does the indigo bunting (Passerina cyanea) look so blue?  It isn’t from the color of his feathers.  In dull light he looks gray!

Last month when I wrote about blue morpho butterflies I learned that their color comes not from pigments but from the structures of their scales that reflect blue light.

This same color trick is what makes indigo buntings’ feathers so blue.

Watch the Deep Look video below to learn how it works.


(photo of indigo bunting by Marcy Cunkelman, video from Deep Look on YouTube)

The Dance Makes A Difference

How can we tell when similar birds are actually different species?

In the jungles of Indonesia the male superb bird of paradise (Lophorina superba) is famous for his courtship dance.  To attract a mate he calls loudly, unfurls his jet black feathers and iridescent green apron, and starts to dance.  If he’s really good at it, the female accepts him.

The bird’s color and dance are so mesmerizing that ornithologists at first dismissed the differences between the eastern and western birds. Now they’ve looked more closely.

This video from Cornell Lab of Ornithology shows how the western bird’s behavior convinced scientists to split the superb bird-of-paradise (Lophorina superba) into two species.

The dance makes a difference.  The bird with the sidestep gait is now called the Vogelkop superb bird-of-paradise (Lophorina niedda).


p.s. Volgelkop is the name of a peninsula in western New Guinea, Indonesia where this bird lives.  On the map the peninsula is shaped like a bird’s head.  Vogel+kop means “Bird head” in Dutch.

(video from Cornell Lab of Ornithology)

Why Ducks Are Hard to Identify in Flight

American wigeon pair on the water (photo from Wikimedia Commons)
American wigeon pair on the water (photo from Wikimedia Commons)

It’s relatively easy to identify ducks on water because they look like the pictures in the field guides.

Even when the female is boring, the male is usually colorful as shown in this pair of American wigeons (Mareca americana).  He’s the one with a green nape, white crown, white butt, and black tail.  The black and white features are unique, even from a distance.

But in flight it’s another story.  Here are three American wigeons in the air.  I’m stumped!

American wigeons in flight (photo from Wikimedia Commons)
American wigeons in flight (photo from Wikimedia Commons)

Why are they so hard to identify? Because we see two body parts that aren’t visible when they’re swimming — bellies and underwings.  Who knew that wigeons have white bellies?

The best way to identify ducks in flight is by using black-and-white drawings.  This Washington Department of Fish and Wildlife brochure is the closest thing I’ve found online:  Ducks at a Distance.  See pages 50-51.


(photos from Wikimedia Commons; click on the images to see the originals)

What The Pigeon Sees

Field of View diagram: pigeon and owl (illustration from Wikimedia Commons)
Field of View diagram: pigeon and owl (illustration from Wikimedia Commons)

How does a pigeon avoid being lunch for a peregrine falcon?

He flies fast, he stays in a flock for protection, and he (quite literally!) keeps an eye out for danger.

Pigeons have such a wide field of view that they can see danger coming from almost any direction.  There’s only a narrow place in front of them where both eyes focus and a narrow blind spot in the back.   Pigeons are not alone. Many prey species have a wide field of view.

This is hard for us to imagine because our eyesight is like the raptor’s but raptors seem to know how it works.  When a peregrine wants to sneak up on a pigeon he flies in the pigeon’s blind spot.

Read more about what the pigeon sees in this vintage article:  Anatomy: Field of View


(illustration from Wikimedia Commons; click on the image to see the original)

Is This Bird Right Handed?

Eurasian kestrel holding a dragonfly (photo by Dr. Raju Kasambe via Wikimedia Commons)
Eurasian kestrel holding a dragonfly (photo by Dr. Raju Kasambe via Wikimedia Commons)

We humans have a trait called handedness in which we show a preference for using one hand over the other.  The vast majority of us are right-handed.

Do birds have handedness, too?

Indeed, they do.  Birds show it by the foot they use, the eye they look out of, and the crossing of their bills.

Feet? Eyes? Crossed Bills?  Read how birds express handedness in this vintage article Anatomy: Right Handed?

So what do you think?  Is this Eurasian kestrel right-handed?


(photo from Wikimedia Commons; click on the image to see the original)

Yellow Is A Sign of Spring

White-throated sparrow (photo from Wikimedia Commons, Creative Commons license)
White-throated sparrow (photo from Wikimedia Commons, Creative Commons license)

Even before the buds burst and the flowers bloom, birds give us a hint that spring is coming.  Some of them turn yellow.

* White-throated sparrows have boring faces in the winter but their lores turn bright yellow ahead of the breeding season. They’ll leave in March or early April for their breeding grounds in the northern U.S. and Canada.

* American goldfinches were brownish all winter but molt into yellow feathers in late winter. Even the females turn a subdued yellow as seen in the female on the left in Marcy’s photo.

Goldfinches turning yellow for spring (photo by Marcy Cunkelman)
Goldfinches turning yellow for spring (photo by Marcy Cunkelman)

* At this time of year European starlings become glossy and their beaks turn yellow.  The starling below is male because the base of his beak is blue (near his face).

European Starling in breeding plumage (photo by Chuck Tague)
European Starling in breeding plumage (photo by Chuck Tague)


There are other birds whose yellow facial skin becomes brighter in the spring.  Can you think of who that might be?  …

Yellow is a sign of spring.


(photos from Wikimedia Commons, Marcy Cunkelman and Chuck Tague. See credits in the captions)