An atavistic claw in a duckling?

The other day I took a picture of this juvenile mallard—one of Honey’s babies—and a friend noticed it had what appeared to be an atavistic claw on its wing. At least I think it’s on its wing; it could be on a  foot tucked behind the bird. But I doubt it.

Here I’ve circled it:

And enlarged it:

The question is whether this is an atavistic claw: the remnant of the claw that was on the reptilian forelimb, and was also prominent in early birds (ignore the labeling of Archaeopteryx as “the earliest known bird”.

Birds also have “spurs“, which are outgrowths of bone that aren’t developmentally homologous to a true claw. But the duckling above seems to have a true claw; it doesn’t look like a bone spur, but is recurved and apparently made of keratin.

Real bird claws, as in the hoatzin,  grow from the digit that’s in the bird wing; in this case it would be the “thumb”. Here’s a “normal” bird.


But birds like hoatzins have true claws, especially in the chicks, which use them to climb back into trees when they fall in the water. I’ve put an Attenborough video of this behavior below the picture, and what it shows is that the claim that a “vestigial” character has to be nonfunctional to be considered vestigial is incorrect. Vestigial traits are simply remnants of traits that evolved earlier but have been coopted for a different function (“exaptations”, Steve Gould might call them). The hoatzin’s claw, very useful for the bird, is certainly a vestigial trait, and is just as much evidence for evolution (of birds from reptiles) as if it were completely nonfunctional.

Some species of waterfowl are known to have these claws (see here and here), but I can’t find something explicitly on mallards.

So we have a mystery here, and I’ve asked a few experts to weigh in. This is either a true atavistic claw in the wing, or one of the claws (nails) in the duck’s rear foot, which could be tucked behind it. You can weigh in, or wait for an answer. Stay tuned.

h/t: Nicole, Greg



  1. Posted June 2, 2020 at 12:45 pm | Permalink

    I find the atavistic remnants (is that redundant?) are fascinating and powerful evidence for EBNS.

  2. ThyroidPlanet
    Posted June 2, 2020 at 12:48 pm | Permalink


  3. ThyroidPlanet
    Posted June 2, 2020 at 12:53 pm | Permalink

    It’s funny but I was just reading about the platypus today, which has a poisonous spur (?).

    • Posted June 2, 2020 at 3:06 pm | Permalink

      Males do, and they use them for fighting and self defense. I have thought that females do not.

  4. GBJames
    Posted June 2, 2020 at 12:54 pm | Permalink

    Awaiting the answer…

    • rickflick
      Posted June 2, 2020 at 3:20 pm | Permalink

      I’ll stand 6 feet behind you.

  5. enl
    Posted June 2, 2020 at 1:00 pm | Permalink

    I made it barely past noon before learning something today. Nice!

  6. Mark Cagnetta
    Posted June 2, 2020 at 1:19 pm | Permalink

    The platypus male sports a similar spur

    • jezgrove
      Posted June 2, 2020 at 2:44 pm | Permalink

      Perhaps it evolved the spur to avoid the draft?

  7. Posted June 2, 2020 at 3:09 pm | Permalink

    I’ve got some ‘hits’ in searches that chickens at least can have wing claws.

  8. Mark R.
    Posted June 2, 2020 at 3:15 pm | Permalink

    Interesting. From the enlargement, it doesn’t look like the claw is from the foot. I’ll be staying tuned.

  9. Jimbo
    Posted June 2, 2020 at 4:00 pm | Permalink

    Maybe ask your duckling rehab guy to see if he’s ever encountered the atavistic claw.

  10. grasshopper
    Posted June 2, 2020 at 5:29 pm | Permalink

    It looks to me like it might be just a pin-feather, though the duckling seems to be very young for a pin-feather of such prominence.

  11. albertonykus
    Posted June 2, 2020 at 8:33 pm | Permalink

    Yes, Anas platyrhynchos can have wing claws (pers. obs. from eating them). Fisher (1940) also documented wing claws in Anas, though he didn’t specify which species.

  12. Jeff Lewis
    Posted June 3, 2020 at 11:45 am | Permalink

    Darren Naish wrote an article about this a few years ago. Apparently, claws are pretty common in modern birds, not just spurs. Here’s a link to his article. Unfortunately, unless my Internet is acting up (always a possibility), it seems the images aren’t appearing.

    • albertonykus
      Posted June 3, 2020 at 9:02 pm | Permalink

      Unfortunately, ScienceBlogs has removed the images from the Tet Zoo articles it hosts. At least the unaltered versions of the articles can still be accessed through Wayback Machine.

  13. Jeff Lewis
    Posted June 3, 2020 at 11:46 am | Permalink

    I don’t know why comments from my other email aren’t showing up, so this may end up being a duplicate comment…

    Darren Naish wrote an article about this a few years ago. Unfortunately (unless my Internet is acting up – always a possibility), the images aren’t showing up on his post.

  14. Andrea Kenner
    Posted June 4, 2020 at 8:21 am | Permalink

    It sure looks like one of my cats’ claws.

  15. Posted June 4, 2020 at 12:07 pm | Permalink

    I used to stuff birds for a museum. I found that ducks usually had very small claws. Coots had larger ones. I never stuffed one, but jacanas are well known to have rather large claws.

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