Wildlife photos: the bizarre Horned Screamer

This tweet isn’t from a reader, but from wildlife illustrator Jessica Roux via Matthew Cobb.  When I first saw this, I thought that some wag had glued horns to a bird:

But no, the Horned Screamer is a real bird! Wikipedia says so!:

The horned screamer (Anhima cornuta) is a member of a small family of birds, the Anhimidae, which occurs in wetlands of tropical South America. There are three screamer species, the other two being the southern screamer and the northern screamer in the genus Chauna. They are related to the ducks, geese and swans, which are in the family Anatidae, but have bills looking more like those of game birds.

Neither Matthew nor I had any idea that such a bird existed:

Here’s a photo of three of them:

And a photo from Arkive:

And the range from the Cornell site; the purple area is the year round breeding and feeding range, and they don’t migrate:

Now as for that “horn”; it really is a horn (my emphasis)

The horned screamer is a massive 84–95 cm (33–37.5 in) long, 3.5 kg (7.7 lb) bird, with a small chicken-like bill. The upperparts, head, and breast are black, with white speckles on the crown, throat and wing coverts. There is a long spiny structure projecting forward from the crown. This structure is unique among birds and is not derived from a feather but is a cornified structure that is loosely attached to the skull and grows continuously while often breaking at its tip.

From Animal Diversity Web (note that they also have bone spurs on their wings):

Horned screamers are large, heavy bodied, fowl-like birds that are most recognizable by their two bone spurs at the bend of each wing and the 15 cm, yellowish-white horn-like projection at the top of their heads. The 2 to 5 cm long bone spurs are a result of fused carpel bones and are covered with keratin. The horn-like projection, which gives these birds their name, is composed of cartilage. When young are born they lack the horn but it slowly grows as they age. Horns seem to be ornamental as they do not have a defensive purpose. They are not firmly attached to the skull, swing back and forth as the birds’ heads move, and are easily broken off. After breaking off they will grow back over time.

A video (you can hear its vocalizations here):

Now your first question will be: why do they have these unicorn horns?

And the answer is, “I have no bloody idea!” My research this morning (granted, enacted at 5 a.m., and without coffee) gives no good answer. Both sexes have the horns, which suggests that it’s either mutual sexual selection or perhaps a form of species recognition, but the males don’t seem to “joust” with these horns, even though the species is territorial.

It seems that little is known about this species. If the horn really is “ornamental”, why it’s there is still unclear. “Ornaments” can be involved in sexual selection, but it’s unlikely that only females use the horn to choose males, for it’s found in both sexes, and natural selection would seem likely to eliminate the metabolically expensive and cumbersome horn in females if they don’t “need” it themselves. Animals don’t have such “ornaments” just to look pretty, so it almost certainly evolved for a reason we don’t yet understand.

Regardless, the horned screamer is the only unicorn bird I know, and the only bird that has a cartilaginous horn.

21 Comments

  1. busterggi
    Posted November 9, 2017 at 7:53 am | Permalink

    Convergent evolution with hot-headed ice borers?

  2. Randall Schenck
    Posted November 9, 2017 at 8:11 am | Permalink

    Seems more like a turkey. Would guess they don’t do a lot of flying.

  3. Posted November 9, 2017 at 8:18 am | Permalink

    That Arkive photo makes me wonder how it manages to eat.

  4. Jorge Rojas
    Posted November 9, 2017 at 8:42 am | Permalink

    I´ve just discover this other beatiful bird in Peruvian Jungle:

    https://en.wikipedia.org/wiki/Marvellous_spatuletail

  5. Dave
    Posted November 9, 2017 at 8:50 am | Permalink

    A thin, cartilaginous rod must have a very low metabolic cost to build and maintain, so it’s probably not a great drain on the owner. If it does have a sexually-selective role, the benefits of having one might outweigh the small cost of secreting it, and the minor inconvenience of carrying it around. After all, male deer produce much larger and more extravagant ornaments, and they have to re-grow them every year.

  6. Ken Kukec
    Posted November 9, 2017 at 8:55 am | Permalink

    … and natural selection would seem likely to eliminate the metabolically expensive and cumbersome horn in females if they don’t “need” it themselves.

    Like teats on a bull?

  7. Yoly
    Posted November 9, 2017 at 9:01 am | Permalink

    Wow, I learn something everyday

  8. DrBrydon
    Posted November 9, 2017 at 9:50 am | Permalink

    Weird.

    Videographer: Look at this bird with the horn– Ooo! Capybara!

  9. Posted November 9, 2017 at 10:02 am | Permalink

    The Milwaukee Zoo has the closely related crested screamer (Chauna sp.), where I’ve seen and photographed them. They didn’t have cephalic horns.

  10. Posted November 9, 2017 at 10:33 am | Permalink

    Reblogged this on The Logical Place.

  11. Michael Fisher
    Posted November 9, 2017 at 10:56 am | Permalink

    That head-bone spur is a ploy to avoid military service

  12. Posted November 9, 2017 at 11:06 am | Permalink

    Weird, but a good reminder that the dinosaurs are still very much among us.

  13. Posted November 9, 2017 at 11:23 am | Permalink

    Going with evolution by natural selection, it could be a structure that was selected for, and is now fallen into disuse and is vestigial.
    It could also be a spandrel; a feature that is not a direct result of natural selection but is made as a developmental by-product of genes under selection for something else.
    It could also be just a feature that became fixed in this species through neutral genetic drift.

  14. boggy
    Posted November 9, 2017 at 11:34 am | Permalink

    I wonder if by any chance this bird may be related to the Invisible Pink Unicorn?

    • busterggi
      Posted November 9, 2017 at 11:37 am | Permalink

      More likely a distant cousin of the White-Winged Narwhal.

  15. Mark R.
    Posted November 9, 2017 at 12:26 pm | Permalink

    Neat bird. With such a large range, I would think it is a common bird, so I’m surprised not much is known about it. Perhaps South America’s jungles impede investigation.

  16. revelator60
    Posted November 9, 2017 at 12:35 pm | Permalink

    This bird is proof that there is no God. Or that he’s a real weirdo.

  17. Posted November 9, 2017 at 2:49 pm | Permalink

    Check out the Horned Guan of a very small area in southwest Mexico and adjacent Guatemala. It has a blazing red horn (made of what I do not know) and is a much rarer bird (and more endangered) than the Horned Screamer which is not difficult to find in S. America.

    • Posted November 9, 2017 at 6:27 pm | Permalink

      I lived on a Mexican volcano for six months looking for that guan and the other special endemics of the area, particularly the Azure-rumped Tanager. The Horned Guan is a magnificent bird! But the Horned Screamer is also amazing. They have a very bizarre sound that carries long distances. They fly well and the local Amazonian tribes say they have bubbles in their bodies so they are lighter than they look.

  18. Posted November 9, 2017 at 7:16 pm | Permalink

    FM Radio. 😛

    Or could it be akin in use to a cat’s whisker or a helpful positioning/balancing device?


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