Last week I read a post on PABIRDS about a spotted towhee in Palmyra, New Jersey in which Barb Heibsch mentioned its scapulars.  That got me thinking.  What are scapulars?

Scapula is the Latin word for shoulder.  In humans it refers to our shoulder blade.

On birds, the scapulars are body feathers that cover the top of the wing when the bird is at rest.  They look like shoulders, as shown circled in pink on this American goldfinch.

Scapular feathers are often unremarkable because they’re the same color as the bird’s back and wings but they’re easy to see on goldfinches because their backs are yellow and their wings are black.

As the breeding season approaches male goldfinches will molt from dull to bright yellow.  Watch their scapulars for signs of spring.

(photo by Marcy Cunkelman, altered to illustrate the scapulars)

Today I’m back to wing anatomy and the huge topic of coverts.

What are wing coverts?

As their name implies these feathers cover the important part of the wing – the flight feathers – and provide contouring so that air flows smoothly during flight.

There are coverts are on both sides of the wing:  upperwing coverts and underwing coverts.  Not only that, they are further divided and named by the part of the wing they cover.

Turkey vultures conveniently have darker underwing coverts than their flight feathers so I’ve marked the vulture pictured here to illustrate them.  The primary underwing coverts are marked in blue, the secondary underwing coverts in pink.

If you look closely inside the blue square you’ll see two layers of primary coverts which overlap like shingles on a roof.  The top layer is called the greater primary coverts.  The second layer, slightly lighter on this bird, is called the lesser primary coverts.  If there are three layers the second one is called the median primary coverts and the third is called lesser.  This three-tiered naming system applies to secondary coverts as well.  On this bird it’s hard to see if he has lesser secondary coverts.  (Have these terms made you cross-eyed yet?)

Upperwing coverts are also named primary, secondary, greater, median and lesser.  These coverts are the wing feathers you see when the bird is perched or standing.  On many birds the upperwing coverts are colorful or striped and provide key clues to identifying the species.  Take a look at warblers and you’ll see what I mean.

So how many kinds of wing coverts are there?  After tantalizing you with the topic I won’t go into it very deeply but here’s a list of as many wing covert names as I can find.  Most of these come in upperwing and underwing varieties:

• Greater primary coverts
• Median primary coverts (I don’t know of an example of these)
• Lesser primary coverts
• Greater secondary coverts
• Median secondary coverts
• Lesser secondary coverts
• Marginal coverts
• Alular quill coverts

Yow!  This is almost boring. Fortunately there will not be a quiz.

(photo by Chuck Tague, altered to illustrate its underwing coverts)

29 December 2009

What limits the size of flying birds? Why are there no behemoths like whales or elephants?

Weight is a limiting factor but it’s not the whole story.  The flightless ostrich weighs up to 300 pounds but our largest airplanes weigh more than 750,000 pounds and they can fly.

The answer is a combination of both weight and flight feathers.  Sievert Rohwer and his colleagues at the Burke Museum found that as a bird’s mass increases its flight feathers must be longer to carry its weight.  However the longer the flight feathers are, the longer it takes for them to grow.

At the high end of body mass the primaries grow so slowly that they’re in danger of wearing out before they can be replaced.  This causes large birds to either molt very slowly – sometimes over a period of years – or, in the case of geese, to lose all their flight feathers at once and hang out in the water until the feathers grow back.

The heaviest flying bird is the kori bustard, pictured above.  Native to the African desert he weighs up to 44 pounds, almost twice the weight of North America’s largest bird, the trumpeter swan, at 23 pounds.

Southwestern Pennsylvania’s heaviest birds are even smaller.  A large male wild turkey weighs 16.2 pounds, a large male Canada goose weighs 9.8 pounds.  My beloved peregrines, though fierce, are lightweights.  The male typically weighs 1.5 pounds, the female 2.2 pounds.

And just because a bird is large doesn’t make him heavy.  The wandering albatross has the longest wingspan at 8.2 to 11.5 feet (up to twice a man’s height) but weighs only 13-26 pounds.

So if a bird wants to fly it can’t weigh much more than 44 pounds — and that’s stretching it.   As you can see, the kori bustard spends a lot of time walking.

For more information see this article in Science Daily or the journal at PLOS Biology.

(photo of a kori bustard by Winfried Bruenken, published under Creative Commons license on Wikipedia.  Click on the photo to see the original.)

I came across the term “patagial mark” at the Allegheny Front Hawk Watch in November when I was having trouble identifying a passing red-tailed hawk.

Usually red-tails are easy for me to pick out by their size, shape and belly bands but the bird in question had a pale belly like the one pictured here, was far away and was fighting the wind.  A fellow birder pointed out that I could always identify a red-tailed hawk if I looked for the “dark patagial marks.”

Patagial?

The patagium is the stretch of skin on the leading edge of the bird’s wing extending from the head to the wrist.  The noun patagium is rarely used but its adjective form, patagial, is fairly common.

For instance, red-tailed hawks have light-colored underwings and a dark patagial mark, shown here circled in pink.  It’s a good field mark because no other hawks in eastern North American have this combination.  Try comparing the underwings of red-tailed hawks to red-shouldered, broad-winged or (western) ferruginous hawks for a bit of fun.

Another use of the word is in “patagial tags” which are bird bands applied to the wing on large soaring birds so that researchers can read the tag while the bird is in flight.  The tag hangs below the wing so it doesn’t interfere with the bird’s ability to fly.  California condors, our biggest bird, have the biggest patagial tags.  Click here to see a patagial-tagged ring-billed gull Chuck Tague saw in Florida last winter.

So, yes, I knew about those dark spots on the red-tail’s wings.  I just didn’t know they were so unique.

(photo by Chuck Tague, altered to highlight the bird’s patagial mark)

Today I’ll wrap up the wing’s flight feathers, parts two and three, secondaries and tertials.

Like the primaries we learned about last week, secondaries and tertials are remiges.  The secondaries run from the wrist to the elbow and hang from a bone called the ulna.  They’re marked here in pink.  Tertials, marked in yellow, run from elbow to armpit and hang from the humerus.  If humans had wings our secondaries and tertials would hang like the sleeve fringe on a buckskin jacket.

The number of secondary feathers varies depending on species, from six in small birds to 40 for an albatross.  Tertials are always few and usually hard to see in flight, especially on songbirds who have 9-10 primaries, 6 secondaries and only 3 tertials.

Tertial feathers are rarely mentioned except in shorebird identification.  That’s because shorebird wing structure is so different that their tertials nearly cover their primaries when their wings are folded.  In fact, when at rest, their tertials lay on top of their tails instead of over their backs.  If I was good at shorebird identification I would be able to look at the tertials and come up with the correct species.  I’d even be able to age the bird.

And finally, even jets have movable secondaries and tertials – or so I like to think.  When birds land they cup their wings and drop their secondaries and tertials to create drag and slow down.  When a jet lands, it lowers two sets of flaps on its wings to do the same thing.

Watch a pigeon land, then watch a jet and you’ll see what I mean.

(photo of a juvenile bald eagle by Chuck Tague, modified to show the secondaries and tertials)

If you’ve been birding for a while you’ve probably heard, even used, the word “primaries” but the word remiges could be new to you. It was to me.

Let’s tackle these two terms in reverse order since remiges are a more general term.

Remiges (pronounced REH.midg.iz) are the flight feathers on a bird’s wing, outlined in red in this picture.

Remiges include all the flight feathers – primaries, secondaries and tertials – and make up the entire trailing edge of the wing.

So what are the primaries?

Answer:  David Sibley describes them as “flight feathers growing from the “hand” bones and forming the lower border of the folded wing.”

The snow goose is an easy example, a white bird with black primaries.  I’ve circled his primaries in green above.

A quick way to think of primary feathers is that they’re where the bird’s fingers would be.  The difference is that there are 9 to 11 of them, sometimes more depending on the species, so they extend around the lower edge of the wing.  If you had 10 fingers on each hand, where would you put them?  Probably where the bird puts his.

Primaries are easy to see on large birds in flight.  Watch soaring red-tailed hawks and you’ll see that they spread their primaries and tip them up to reduce wingtip vortex.   Aircraft engineers design upturned wingtips on airplanes for the same reason.

So… the primaries are feathers where the birds fingers would be, and all primaries are remiges (wing flight feathers) but not all remiges are primaries.

(photo of snow geese from Wikipedia)

Winter is lousy for field work but it’s a good time to curl up with a book and learn something, so in that spirit I’ve decided to (finally!) learn more about bird anatomy. 

Yes, I’ve watched birds for decades but that doesn’t mean I know the scientific names for the parts of a bird.  During research on various blogs I’ve encountered many technical names, but what do they mean? 

Maybe the names stump you, too.  Why not make this a group project?  So here’s the first in a weekly series on bird anatomy. 

What is a culmen?  It sounds vaguely like… ummmm…. “culminate,” a related word. 

Answer:  It’s “the dorsal ridge of the bird’s bill.”  For us laypeople, it’s the top of the beak from the head to the tip, as shown by the green line. 

I encountered “culmen” when I looked for the length of the pileated woodpecker’s beak.  The answer was “the male’s culmen is 43-56 mm” so I had to look up two things:  the meaning of culmen and the conversion from millimeters to inches.

The shape of the culmen is a useful field mark for identifying birds.  Some bills (culmen) curve up as on American avocets, some are straight, and some curve down as on the long-billed curlew.

So now you know.

(photo by Chuck Tague with graphics added by Kate St. John)