Dec 04 2009

Anatomy: Secondaries and Tertials

Published by at 7:10 am under Bird Anatomy

Bald eagle with secondaries and tertials marked (photo by Chuck Tague)
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)

3 responses so far

3 Responses to “Anatomy: Secondaries and Tertials”

  1. Dianeon 04 Dec 2009 at 12:10 pm

    You make this so informative and interesting. I really appreciate it and look forward to every new lesson. Thanks so much.

  2. Geneon 04 Dec 2009 at 8:08 pm

    Love your site, it is very informative.

    What you refer to as a jet’s fin is actually called a flap. Most aircraft have flaps on the trailing edge of their main wing. Bigger aircraft also have leading edge wing slats. Together these give the wing a more curved profile which enables the aircraft to get more lift at slower speeds, needed when taking off and especially landing. As you also point out, birds do this through their very flexible wing structure. Also, jets and many aircraft have plates on top of the wing called spoilers. These plates tilt up and are hinged toward the front. They are used during landing approach and after touch down to interrupt good lifting airflow. Birds, on the other hand, just fold their wings partially or fully to get the same lift losing effect.

    Anyway, the comparison between birds and man made flying machines is always a fun exercise to observe.

    Cheers, and thank you for sharing your knowledge,


  3. Kate St. Johnon 05 Dec 2009 at 6:59 am

    Gene, thanks for the airplane anatomy lesson! I corrected “fins” to “flaps” in the original post. I’ve watched those airplane parts in action for years but didn’t know their correct names. When I fly I like to sit over the wing and see the wings go through their paces for take-off, steady flight and landing. Very cool stuff.

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