Category Archives: Bird Anatomy

Seven Streaked and Spotted

Bird Anatomy, Costa Rica, Travel
Fasciated tiger-heron, Costa Rica (photo from Wikimedia Commons)

5 February 2026

Understory birds in Costa Rica’s rainforest are often streaked, spotted and striped for camouflage while they move in dim and dappled light near the forest floor. Out of all those streaky birds I have seven favorites from my trip to Costa Rica last month. Six are forest skulkers, the seventh, shown at top, is not an understory bird at all so I don’t know why he’s striped. NOTE: These photos are not to scale; almost all of them are from Wikimedia Commons.

Fasciated Tiger-Heron (Tigrisoma fasciatum)

The best way to see a fasciated tiger-heron is to check the edge of a rushing stream. We found two fishing in the Sarapiquí River at Selva Verde Lodge. Obviously the stripes do not camouflage them in this setting. Maybe those stripes are for a different reason.

Fasciated Antshrike (Cymbilaimus lineatus)

This species posed nicely for us. He also posed for his Wikimedia Commons photo below.

The Fasciated Antshrike forages, mostly for large insects, in the midstory of tropical lowland forest. He’s found in vine tangles and dense mid-story canopy.

— Birds of the world account
Fasciated antshrike, male (photo from Wikimedia Commons)
Streak-crowned Antvireo (Dysithamnus striaticeps)

I saw this Life Bird during the Sky Walk at Arenal while there was a pause in the pouring rain. He was on my Wish List.

The streak-crowned antvireo ranges from Honduras through Nicaragua to Costa Rica, living in the understory and mid-story of lowland and foothill evergreen forest. He forages for insects and is often in mixed species flocks (paraphrased from Birds of the World).

Streak-crowned antvireo (photo from Wikimedia Commons)
Spotted Antbird (Hylophylax naevioides)

Spotted antbirds are …

Frequent–though not obligate–followers of mixed-species foraging flocks that track insect-flushing swarms of army ants across the forest floor.

The Spotted Antbird’s scientific name means a “spotted watcher of the woodland.” In Panama’s Darien province the species is locally known as ‘corregidor‘ (mayor) for its apparent behavior of directing the activities of other birds found with it, presumably at army ant swarms.

— paraphrased from Birds of the World
Spotted antbird (photo from Wikimedia Commons)
Spot-breasted Wren (Pheugopedius maculipectus)

What a skulker! This bird is said to be common but it is very hard to see.

Generally common. Found in a wide variety of wooded habitats, including second growth and plantations, where it forages, apparently for insects in low tangles and other dense vegetation.

— paraphrased from Birds of the World

For a brighter photo, see this one from Wikimedia Commons.

Stripe-breasted Wren (Cantorchilus thoracicus)

Very cute wren more often heard than seen.

The Stripe-breasted Wren has two distinct singing ‘styles’, which are sufficiently at variance to sound as if they were made by completely different types of birds. The first is a series of whistles on the same pitch, somewhat like the calls of a small owl, which song, usually given at dawn, is typically given by a single bird. The second is a series of up to ten bubbling whistles, which is far more typical of the Troglodytidae, and is given in a duet.

— from Birds of the world
Stripe-breasted wren (photo from Wikimedia Commons)
Bay Wren (Cantorchilus nigricapillus)

When this wren turns his back on you, you can’t see him. If he hadn’t shown his chest I would never have known he has stripes. No photos from the trip; all I have are happy memories. These photos are from Wikimedia Commons.

Bay wren back and chest (photos from Wikimedia Commons)

Beauty With a Blind Spot

Bird Anatomy, Doves & Chickens
Male golden pheasant (photo from Wikimedia Commons)

17 December 2025

The male golden pheasant (Chrysolophus pictus), native to forests in western China, is one of the showiest birds on earth. He’s bright red, orange, yellow and blue with a tail twice as long as his body and a black-and-orange ruff that displays to cover his face, except for his eyes.

Male golden pheasant (photo from Wikimedia Commons)

His beauty is aimed to impress the ladies. Female golden pheasants prefer outrageous males so their mate selection drives male plumage evolution. Fortunately the males don’t incubate eggs. The females are dull colored for camouflage on the nest.

Female golden pheasant (photo from Wikimedia Commons)

Birds hunted by predators usually have a wide field of view so they can see danger coming from every angle. Pheasants, like pigeons in the diagram below, usually see almost 360° without turning their heads.

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

But not the male golden pheasant. His fancy head feathers block his field of view above and behind his head. If you can’t see at least one of his eyes, he can’t see you. This guy has a huge blind spot.

Male golden pheasant, back of head (photo from Wikimedia Commons)

Golden pheasants are not the only species with this problem. Male Lady Amherst’s pheasants (Chrysolophus amherstiae) also have a blind spot, especially when they display.

Find out more in the New York Times: He’s Beautiful, but He Has a Huge Blind Spot.

Fortunately, Flapping Saves Energy

Bird Anatomy, Migration
American robin in flight (photo from Wikimedia Commons)

2 October 2025

The mix of migrating songbirds is changing this month, but migration is still in full swing. When the weather is right, songbirds take off an hour+ after dusk and may fly eight hours to stop just before dawn. Last week was especially intense for migration, as described by BirdCasts’s Kyle Horton for NBC 7 San Diego.

All of these nighttime migrants are flapping. How much energy does this use up?

Back in 2005 a biotelemetry study of Swainson’s thrushes measured heartbeat and wingbeats in flight and concluded that they flapped about 11 beats per second on sustained migration. In eight hours that means about 311,000 wingbeats — a lot of flapping for a small bird — and some of them flap even more, such as the ruby-crowned kinglets who’ve just started to pass through our area.

Ruby-crowned kinglet in flight (photo from Wikimedia Commons)

Amazingly, flapping is more efficient than soaring. Find out why in this vintage article from 2017.

Flapping Saves Energy

Birds Are Shrinking and This is Normal

Bird Anatomy, Climate Change
Examining wing of Tennessee warbler during banding, Bird Lab at Hays Woods, 16 Sep 2025 (photo by Kate St. John)

30 September 2025. Old news but worth a look.

Lots of data is collected when a bird is banded or collected in a museum including species, sex, age, weight, wing and tarsus length. When nearly half a century of this data was analyzed at Powdermill in 2010 and at Chicago’s Field Museum in 2019 it became apparent that very slowly, over a period of nearly half a century, North American birds have been shrinking and in many cases their wings are getting longer.

Measuring the wing of Lincoln sparrow during banding (photo from Wikimedia Commons)

The Powdermill and Field Museum studies both found a correlation between size change and the annual mean summer temperature of the species’ breeding range. They reached the same conclusion: As the climate heats up, migratory birds are getting smaller.

What about birds that never migrate?

A similar study in 2021 at the Amazon Biodiversity Center in Brazil analyzed 40 years of data on 77 species and found the same thing. Nearly every non-migratory species became smaller and 1/3 of them had longer wings. Warmer climate was the only known variable at that site.

Golden-crowned spadebill banding, Amazonian Ecuador (photo from Wikimedia Commons)

So many places on Earth are getting warmer, even the Amazon as shown on this temperature anomaly map from 2024.

Earth’s surface temperature anomaly in 2024, plus graph of the last 48 years of temperature anomalies relative to 20th century average temperature (from NOAA)

The birds are shrinking and this is normal. Very slowly, as their home territories heat up, bird bodies are following Bergmann’s Rule regarding body size and temperature.

Bergmann’s Rule: Within a species, populations living in colder climates have larger body size than those in warmer climates. Large animals have a lower surface-area-to-volume ratio so they lose heat more slowly in cold climates. Small animals have a higher surface-to-volume ratio and cool off faster when it’s hot.

To see this side-by-side, check out these song sparrows (Melospiza melodia) in the Carnegie Museum of Natural History’s Section of Birds. Song sparrows collected in Pennsylvania (on the left) are small and in Alaska (right) are large. Southern : warm : small. Northern : cold : large.

Song sparrow geographic size difference, Pennsylvania on left, Alaska on right from Carnegie Museum of Natural History Collection (photo by Kate St. John, Dec 2016)

Birds are adapting to climate change generation after generation.

Redstarts Have “Whiskers”

Bird Anatomy
Female American redstart closeup to show rictal bristles, 16 Sept 2025, Bird Lab at Hays Woods (photo by Kate St. John)

18 September 2025

When I visited Bird Lab’s Hays Woods banding site on Tuesday, I was excited to release an American redstart after she was banded, weighed and measured. Before I let her go I took a good look at her face and was surprised to see she had rictal bristles around her beak. On cats we’d call them “whiskers.”

Rictal bristles are stiff, modified bristle feathers that grow at the base of the birds beak — at the gape, or the nares (nostrils), the lores, or beneath the beak. They may or may not have barbs. They are not like other feathers.

Diagram of location and shape of rictal bristles. From Nature.com (open access): The evolutionary origin of avian facial bristles and the likely role of rictal bristles in feeding ecology.

Years ago I’d heard that rictal bristles were used to help capture flying-insect food but experiments have shown that is not the case.

Studies [published in SORA] have been done where the bristles of [willow] flycatcher were removed or were taped down. Neither of those actions adversely affected the birds’ ability to capture prey, indicating that the rictal bristles do not aid in prey capture. In those studies the flycatchers that had their rictal bristles taped down or removed had more debris from their insect prey land on their eyes.

— Mia McPherson: Willow Flycatcher Up Close – What Are Rictal Bristles?

Now that the food capture theory has been thrown out, new studies are looking into the evolutionary origin of avian facial bristles — how many birds have them? Other studies are trying to parse out the feathers’ purpose. Some bristles may protect the eyes or nose. Some may be tactile, just like cats’ whiskers. Some are a mystery.

And that’s where redstarts come in; their bristles made me wonder. Here are better looks at their faces.

American redstart at Magee Marsh (photo from Wikimedia Commons)
Male American redstart (photo from Wikimedia Commons)

Why do American redstarts have rictal bristles? More study needed.

Juvie Pitt Peregrine Comes Home to Complain

Bird Anatomy, Peregrines
Juvie peregrine “Yellow” whines at the nest, 21 July 2025, 5:04pm (snapshot from the National Aviary falconcam at Univ of Pittsburgh)

1 August 2025

Streaming has ended for the season at the National Aviary falconcam, but just before it ended …

On 21 July all three of this year’s young peregrines had been gone from the Cathedral of Learning for more than a month when — Surprise! — a very loud juvie chased Ecco to the nest.

Apparently tired of fending for herself, Yellow arrived on the scene to demand food from her father. But like all good peregrine parents, Ecco would not feed her. She complained bitterly. “I don’t wanna grow up!”

Ecco and immature “Yellow” at the Pitt peregrine nest on 21 July 2025, 5:00pm (video from the National Aviary falconcam at Univ of Pittsburgh)

Things went back to normal for a while but six days later, on 27 July, Ecco and Carla arrived at the nest for a bonding session. They had to leave abruptly when a noisy youngster showed up off camera. It was probably Yellow.

Ecco and Carla avoid a noisy youngster off camera, 27 July 2025, 2:45pm (video from the National Aviary falconcam at Univ of Pittsburgh)

Eventually Yellow will get the hint, leave the area and finally grow up. I can imagine Carla telling her, “May you have many children just like you.”

p.s. News from Downtown: I’m happy to see the Downtown peregrines are controlling the airspace.

eBird Checklist S258389927
Wed 9 Jul 2025, 12:24 PM
One Oxford Centre, 426–518 4th Ave, Pittsburgh US-PA (40.4383,-79.9986)
Reported by: MONTGOMERY BROWN
1 Peregrine Falcon (Falco peregrinus)

The falcon was “harassing” a drone that was 350-400 feet off the ground. After about 30 seconds, the drone operator appeared to realize this and flew the drone off toward the Monongahela.

A Canada Goose the Size of a Pigeon?

Bird Anatomy, Water and Shore
“The Canada Goose at Kennedy Lake is quite tame.” (photo by Brent Myers via Flickr Creative Commons license)

7 April 2025

UPDATE: Thank you Amber VanStrien for pointing out that Wild Bird Fund posted this “news” on APRIL FOOL’S DAY … And I fell for it. However, there really are dwarf geese that are less than half the size (44%) of a normal Canada Goose. See revised text below.

Typical Canada geese, like the one shown above, are large birds as tall as our knees when relaxed and foraging and bigger when angry. You can’t hold one in the palm of your hand so I was amazed to see this photo of a Canada goose in New York City that is only the size of a pigeon! (Hah! It’s an April Fool’s joke.)

“Lilligoosian” was supposedly in rehab at the Wild Bird Fund on Columbus Ave, Upper West Side, NYC –> 1/10th the size of a normal Canada goose, half the size of a mallard, and just a few grams heavier than a male pigeon.

Do very small birds like this exist?

David Sibley explains in his article Do “dwarf” birds exist? that “continued poor nutrition [during the gosling stage] results in birds that never reach full size and remain smaller than normal, as several studies on Snow and Canada Geese have shown.” For instance, from a study in 2015:

Canada goose goslings fed low-protein (10%) diets were on average 44% lighter in body mass, had slower growth rates and were delayed >20 days in reaching 90% of asymptotic size compared with Canada goose goslings fed 18% protein.

— from Ecological implications of reduced forage quality on growth and survival of sympatric geese

So “Lilligoosian,” the pigeon-sized Canada goose, was probably Photoshop’d but there are such things as dwarf geese. Goslings can be stunted by unhealthy food and reach only half the size of a normal Canada goose in adulthood.

Why Owls Can Turn Their Heads So Far

Bird Anatomy, Birds of Prey
Great horned owl with head facing over its back (photo from Wikimedia Commons)

13 March 2025

Owls have excellent eyesight but they see the world differently than we do.

When we look straight ahead (fixation point below) our peripheral vision allows us to faintly see our hand waving near our ear — a 200-220° field of view.

Human field of view (diagram from Wikimedia Commons)

Owls have binocular vision similar to ours but their peripheral vision is much narrower. They cannot even see 180°.

Field of View diagram for owl derived from an illustration on Wikimedia Commons

To make matters worse they cannot move their eyes!

Great horned owl eye closeup (photo from Wikimedia Commons)

Since their eyes are always facing forward, they have to move their heads or their bodies to see anything outside their narrow field of view. Moving their bodies would alert their prey, so owls have evolved to move their heads as far back as they need to see — up to 270°.

  • Owls have 14 neck bones for greater flexibility. We have only 7 neck bones
  • The owls’ atlanto-occipital neck joint has evolved to move the head further back.

When you can’t move your eyes, you have to move your head.

video embedded from Garry Hayes on YouTube

Rare and Wonderful White Hawk

Bird Anatomy, Birds of Prey
Leucistic red-tailed hawk in Northampton County, PA, 4 Jan 2025 (photo by Brenda Lindsey)

9 January 2025

There were several hours of excitement on New Years Day when a snowy owl showed up at Pymatuning. That same day in Northampton County, PA Steve Magditch thought he too may have found a snowy owl but his camera lens revealed a common bird in uncommon plumage, a leucistic red-tailed hawk (Buteo jamaicensis).

Brenda Lindsey was excited to capture these photos on 4 January.

Leucistic Red-tailed Hawk! I set out this morning to (maybe) see it. (I can’t believe I found it!) Thank you Steve Magditch and Kathleen Itterly Dimmich for your prior postings of this unique Bird of Prey!

— Brenda Lindsey post on Facebook, 4 January 2025

This white hawk is called leucistic, not albino, because it has normal-colored eyes and at least one normally colored feather. See the red feather(s) in its tail.

Leucistic red-tailed hawk in Northampton County, PA, 4 Jan 2025 (photo by Brenda Lindsey)
Leucistic red-tailed hawk in Northampton County, PA, 4 Jan 2025 (photo by Brenda Lindsey)

Though rare, leucistic red-tailed hawks occur throughout their range in North America with a lot of variation in their plumage. Some are spotted, some are blotchy.

See additional photos of white red-tails and learn about leucism in this vintage article.

Who Is This White Hawk?