Tetrapod Zoology

Perhaps the weirdest chicks of all

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What is this bizarre fuzzy little creature? It’s a Black coucal Centropus grillii chick, and what makes it particularly interesting is that it’s covered with simple, tubular, unbranched feathers (termed trichoptiles). If you know the literature on the evolutionary development of feathers you will have noticed that trichoptiles look suspiciously similar to the ‘stage 1 feathers’ hypothesised by Prum and Brush, and yet here they are in a neornithine. They rarely get a mention, despite being described by Shelford (1900), and despite being present elsewhere in cuculiforms and not restricted to the rather obscure and poorly known coucals: Kaiser (2005), for example, described them in roadrunner chicks.

Even without the trichoptiles of their nestlings, coucals are very neat birds. They are large, long-tailed terrestrial cuckoos of the Old World and Australasian tropics (c. 30 species) with enlarged hallux claws, rounded wings and high wing-loadings, and studies generally find them to be close to the base of the cuculiform radiation (Hughes 2000, Johnson et al. 2000, Sorenson & Payne 2005). Stalking through the undergrowth in search of arthropods and small vertebrates, they behave more like pheasants than cuckoos (an Australasian species is in fact called the Pheasant coucal C. phasianus), and it has often been noted that they have a superficially reptilian look about them. Indeed Feduccia and others have drawn attention to the fact that coucals strongly resemble archaeopterygids in size and proportions (this is not entirely accurate however, as the fossils show that archaeopterygids were substantially less neornithine-like than Feduccia says).

Coucals are communal breeders, the females are larger than the males, and in fact the males are often responsible for nest-building, incubation duties, and for care of the young (Andersson 1995, Maurer 2008). Males also routinely have one of their testes atrophied. Polyandry has evolved in C. grillii, and the reliance on males as the primary carers have uniquely made the Black coucal the only polyandrous bird known in which the nestlings are not precocial (Goymann et al. 2004, 2005, Goymann & Wingfield 2004).

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The pictures were kindly provided by Greg Davies of Natal Museum, and Greg also provided a lot of helpful information and references on coucal trichoptiles and behaviour.

Refs – –

Andersson, M. 1995. Evolution of reversed sex roles, sexual size dimorphism, and mating system in coucals (Centropodidae, Aves). Biological Journal of the Linnean Society 54, 173-181.

Goymann, W., Kempenaers, B. & Wingfield, J. 2005. Breeding biology, sexually dimorphic development and nestling testosterone concentrations of the classically polyandrous African black coucal, Centropus grillii. Journal of Ornithology 146, 314-324.

– . & Wingfield, J. C. 2004. Competing females and caring males II. Sex steroids in African black coucals, Centropus grillii. Animal Behaviour 68, 733-740.

– ., Wittenzellner, A. & Wingfield, J. C. 2004. Competing females and caring males I. Polyandry and sex-role reversal in African black coucals, Centropus grillii. Ethology 110, 807-823.

Hughes, J. M. 2000. Monophyly and phylogeny of cuckoos (Aves, Cuculidae) inferred from osteological characters. Zoological Journal of the Linnean Society 130, 263-307.

Johnson, K. P., Goodman, S. M. & Lanyon, S. M. 2000. A phylogenetic study of the Malagasy couas with insights into cuckoo relationships. Molecular Phylogenetics and Evolution 14, 436-444.

Kaiser, M. 2005. Haltung und Zucht des Rennkuckucks, Geococcyx californianus (Lesson, 1829), im Tierpark Berlin. Milu 11, 448-461.

Maurer, G. 2008. Who cares? Males provide most parental care in a monogamous nesting cuckoo. Ethology 114, 540-547.

Shelford, R. 1900. On the pterylosis of the embryos and nestlings of Centropus sinensis. Ibis 1900, 654-667.

Sorenson, M. D. & Payne, R. B. 2005. Molecular systematics: cuckoo phylogeny inferred from mitochondrial DNA sequences. In Payne, R. B. (ed) Bird Families of the World: Cuckoos. Oxford University Press, pp. 68-94.

Comments

  1. #1 chris y
    October 15, 2008

    If it’s not too dumb a question, what do they reckon the trichoptiles are for? They look too skimpy to provide much insulation. Do they have some kind of sensory function?

  2. #2 Jerzy
    October 15, 2008

    I always wondered if down of chicks and ducklings is homologous with insulation of non-avian theropods. Ontogeny recapitulates phylogeny etc.

    I seen Redshank chicks, feeding for themselves with parents loosely hanging by, and they looked like tiny dinosaurs.

  3. #3 El PaleoFreak
    October 15, 2008

    Very interesting. Googling for “trichoptyle” I found this one:

    Independent origin of the trichoptile and neoptile in bird plumage

  4. #4 Adam Yates
    October 15, 2008

    How interesting. I just had my first good look at the local coucal species (Centropus burchelli) just yesterday morning, once again out my back window in the very same bush that the weaver featured on my blog was infront of. They are common in Johannesburg but very shy and difficult to get a good look at.

  5. #5 Hai~Ren
    October 15, 2008

    Coucals are neat birds; I see them quite rarely, but they are quite unmistakable.

    If I’m not wrong, the greater coucal (Centropus sinensis) is also known as the crow pheasant.

  6. #6 Moro
    October 15, 2008

    Maybe the trichoptiles make the baby coucals distasteful to predators. I mean, would you want to put that in your mouth?

  7. #7 Quietman
    October 15, 2008

    Why do trichoptiles need a function? The mutation of a harmless trait can either go away or continue development. It’s just how evolution works. This species simply retained an ancient trait.

  8. #8 John Scanlon FCD
    October 15, 2008

    I usually see Pheasant coucals only as a heap of gorgeously patterned feathers at the side of the road; they are not very good at dodging cars. But the other day as I was on my way out of work there was one in the carpark, scuttling along the base of the wall between shrubs – if it hadn’t moved, I almost certainly wouldn’t have spotted it crouched with wings and tail spread. It’s impossible to see one alive and not think of Archaeopteryx, but the most ‘dinosaurian’ bird we get around here is the Apostle bird Struthidea cinerea; not the morphology so much as the behaviour of a mob of them, swaggering around on the ground (more Velociraptor than Procompsognathus), fighting over food and making very Jurassic-Parkish noises.

  9. #9 Dartian
    October 16, 2008

    Maybe the trichoptiles make the baby coucals distasteful to predators. I mean, would you want to put that in your mouth?

    But surely this bird must be edible; why else would someone have named it grillii?
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    Just kidding, of course. Unless I’m mistaken, this species is named after the Swedish naturalist Adolf Grill (1752-1797).

  10. #10 Darren Naish
    October 16, 2008

    Actually, I think that Centropus grillii (which was named by Gustav Hartlaub in 1861) was named in honour of Johan Wilhelm Grill (1815-1864). Hartlaub published the first description of the species in Journal für Ornithologie, a journal that he himself had started (with Jean Cabanis) in 1851.

  11. #11 Dartian
    October 16, 2008

    Darren Naish:

    Actually, I think that Centropus grillii (which was named by Gustav Hartlaub in 1861) was named in honour of Johan Wilhelm Grill (1815-1864).

    Really? Didn’t know that. I stand corrected.

  12. #12 Jerzy
    October 16, 2008

    Actually, coucals are indeed very similar in proportion to Archeopteryx. Among others, they fly poorly and for short distances, and are tireless walkers but not fast runners. Which blows some of stranger restorations of A. lithographica – e.g. as a good flyer or waterbird.

    I imagine that in semi-desert islands which made Jurassic European environment, some small coucal-like thingy stalked lizards creeping between the bushes. These things dispersed between islands, and some were swept by sea.

    It would be interesting study to study joints of skeleton of Hoatzin chick and see if range of movements is similar to dromaeosaurids and which dromaeosaurids. It would give invaluable insight on how these things moved and climbed.

  13. #13 Darren Naish
    October 16, 2008

    Jerzy says…

    Actually, coucals are indeed very similar in proportion to Archeopteryx.

    Well, no… they are only very superficially similar. What reconstructions of Archaeopteryx are you looking at? And do you have the papers on the 10th (= Thermopolis) specimen? Note that most classic restorations of Archaeopteryx make it look far too much like a modern bird. Even the photos in Feduccia’s book (which show a coucal skeleton arranged to match the death posture of the Berlin Archaeopteryx: p. 107 in his 1996 The Origin and Evolution of Birds) reveal major differences in all proportions: the coucal has a much shorter back, shorter legs, fully anisodactyl feet [WHOOPS – see below] with an enlarged hallux and very long hallux claw, very differently proportioned arms, much shorter hands, a far more rounded wing, and a tail that consists of parallel elongate rectrices.

  14. #14 Tengu
    October 16, 2008

    You`re right, very different.

    Do you think the feathers are concealment (not camoflage as such; just making the chick look very funny and not at all edible) it would fool a visual predator if the chick kept still

    On a completley unrelated note, there is an albino sparrow living in the vicinity of Dads…hes going to try to photo it

  15. #15 Brian
    October 16, 2008

    Darren,

    I take it the ‘fully anisodactyl feet’ on a coucal is a slip of the keyboard? At least, I was pretty sure all cuculiforms are zygodactylous.(That is unless you want to include the hoatzin, of course)

    By the way, on a obsolete linnean note: would you consider coucals centropodines or centropodids?

  16. #16 Darren Naish
    October 16, 2008

    Whoops, what a dumbass I am, thanks Brian. I had the fully reversed hallux in mind and forgot about the rest of the foot. Of course, all cuckoos are zygodactyl.

    As for classification, I know that some people are advocating a Centropodidae for coucals, but I don’t much see the point. Sibley & Ahlquist recommended that ‘Cuculidae’ of tradition be split up into Cuculidae s.s., Centropodidae, Coccyzidae, Crotophagidae and Neomorphidae (and they included Opisthocomidae within their Cuculiformes as well), but this hasn’t caught on: look at Robert Payne’s recent OUP book on cuckoos, for example. Therein, all of the groups listed above (except hoatzins, and with the addition of couines) are ‘subfamilies’ within ‘family’ Cuculidae.

  17. #17 Jerzy
    October 17, 2008

    Darren,

    So which living bird is closer in body proportions to Archaeopteryx? Without caring about claws, I guess A. compensated with wing claws for short foot claws.

  18. #18 Sven DiMilo
    October 17, 2008

    Perhaps the weirdest chicks of all

    Clearly, you don’t know my ex-wife.

    ba-dump chshhhh

  19. #19 Ed Pardo
    October 22, 2008

    Epidexipteryx would seem to have some type or form of trichoptiles as a tail.

  20. #20 sara
    November 11, 2008

    Here is a Roadrunner chick sporting trichoptiles and zygodactyly. Do you know if trichoptiles are restricted to Cuculiformes? In the paper by Ilyashenko, he reported trichoptiles in Rails and Falcons as well as Cuckoos, but I did not really understand his criteria. And do you know the term for natal plumage of Ostriches? I am not up to date on all of the -ptiles yet.

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