Tetrapod Zoology

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ResearchBlogging.org

We didn’t just go to the New Forest on Sunday to look at crossbills, fantastic and charismatic as they are. The main reason for the trip was the visit to Blackwater Arboretum: a locally renowned roosting site for…. Hawfinch Coccothraustes coccothraustes. The site is so renowned that, at this time of year, a large number of people turn up in the later afternoon to watch the birds come in to roost. A wooden carving that appears to depict a hawfinch (confusingly, the accompanying plaque tells you that the carving is named ‘Fire crest’ [sic]) can be found at the site, as you see from the adjacent image.

The Hawfinch is a remarkable and unmistakeable finch. Robust, stocky and short-tailed, it sports bizarre curled tips to its inner primaries and a characteristically massive bill. This is used to crack open the kernels of plums, cherries, maples and other pits and stones and the bird is able to literally crack these rock-hard objects in half. Reaching 18 cm in total length and weighing c. 54 g, it is one of the largest finches of the European field guide region. Some books say that it is the region’s largest finch, but it is matched or exceeded by the White-winged grosbeak Mycerobas carnipes (known from Iran eastwards to China), Caucasian great rosefinch Carpodacus rubicilla (the most westerly subspecies of which inhabits the central and eastern parts of the Caucasus), and Pine grosbeak Pinicola enucleator (the nominate subspecies of which occurs in Scandinavia). All of these are pretty obscure and exotic finches, or they are if you live in Britain at least.

We saw our first hawfinch some time around 15:30, and I’m pleased to say that the very first individual that turned up was first spotted by a member of our natural history group. It sat right at the top of a bare conifer for some time over ten minutes, in an unusual display of lethargy uncharacteristic for a small passerine. Within an hour between five and ten birds had appeared and, after most people had left, those of us remaining were treated to a view of 16 birds in the same tree. Like most small birds, they don’t of course sit out in the open at night, but deliberately tuck themselves in among dense foliage. Several conifers in the arboretum seem to be favoured for this purpose.

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The Hawfinch is unique (or is it? Read on): it’s usually imagined to be closely related to grosbeaks but is the only member of its genus, Coccothraustes. Actually, this wasn’t the case for much of the twentieth century, as until fairly recently various Asian and North American grosbeaks now included in the genera Mycerobas and Hesperiphona were regarded as additional species of the hawfinch genus. There are also several hawfinch subspecies – most of which differ from the nominate Eurasian form in being paler, darker, or slightly smaller – and it’s always possible that (as is the case with so many ‘subspecies’ these days) at least some of these will be regarded by some workers as worthy of specific status. I’d speculate that this is most likely for C. c. buvryi of northern Africa, a hawfinch notable in having a more gracile bill than the other forms. There are also a few fossil hawfinch species, with C. balcanicus and C. simeonovi both named from the late Pliocene of Bulgaria (Boev 1998). So the hawfinch may not be so unique after all. I’ve actually spent some considerable time trying to find a tetrapod that is truly unique: without any close living or extinct relatives. So far no luck. Let me know if you think of one [adjacent hawfinch image from here].

As with the crossbills I discussed in the previous article, hawfinches are part of the finch clade Carduelinae, the group that also includes grosbeaks, bullfinches, rosefinches, goldfinches, redpolls and siskins. Phylogenetic studies support the view that the hawfinch is ‘unique’: Arnaiz-Villena et al. (2001) found it to represent an isolated lineage most closely related to bullfinches (Pyrrhula) and grosbeaks (Mycerobus). If this is correct then hawfinches are relatively basal within Carduelinae and have a ghost lineage going back to the late Miocene, but there are few phylogenetic studies of carduelines and further study is needed before we can be really confident about this.

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Given its massive bill and (assumed) impressive bite, there has been quite some discussion in the literature as to what these birds are capable of in biomechanical terms. The hawfinch skull is massive, deep-jawed, equipped with a particularly long and well-reinforced symphysis in the mandible, and with hypertrophied musculature. Both Sims (1955) and Bock (1966) discussed hawfinch bite strength, the former in a study of hawfinch cranial morphology and the latter in a paper on bill form and function. Van der Meij (2004) tabulated the amount of jaw musculature a hawfinch has (an incredible 1454 mg: most other carduelines have between 120 and 600 mg), and while she recorded bite forces for carduelines and other finches she didn’t manage to get this data for hawfinches.

Cracking open a cherry stone apparently requires a force of 27-57 kg: Witmer & Rose (1991) stated that this was about equivalent to 470-700 N while van der Meij & Bout (2004) discussed the force produced by the hawfinch bill as being 310 N. Both Sims and Bock go into a bit of detail as to what this actually means for how the finch’s bill is loaded during biting, and where the compression and so on occurs. I’m rubbish on biomechanics so won’t attempt to discuss it, but I’m sure the data is very impressive if you can understand it properly [adjacent hawfinch pic from here].

Anyway, I’d never seen a single hawfinch before, so to be suddenly saturated with a mass sighting of 16 birds at once, at quite close range, was a great experience. They looked fantastic. They weren’t the only finches there: we also watched siskins and bramblings too, and there were also goldcrests and firecrests in the area. Later that day Phil Budd and I went off to look for a Black-throated diver presently haunting the New Forest, but I’d better stop there otherwise I’ll end up writing yet more about birds.

So in a deliberate effort to avoid birds, I’ll be getting back soon to vampire bats. Will (aged 5) encouraged me to do some internet research on Godzilla recently, so you can look forward to the soon-to-appear ‘The science of Godzilla’ post (really). There is also some stuff close to completion on Piltdown, at last.

Refs – -

Arnaiz-Villena A, Guillén J, Ruiz-del-Valle V, Lowy E, Zamora J, Varela P, Stefani D, & Allende LM (2001). Phylogeography of crossbills, bullfinches, grosbeaks, and rosefinches. Cellular and molecular life sciences : CMLS, 58 (8), 1159-66 PMID: 11529508

Bock, W. J. 1966. An approach to the functional analysis of bill shape. The Auk 83, 10-51.

Boev, Z. 1998. Late Pliocene hawfinches (Coccothraustes Brisson, 1760) (Aves: Fringillidae) from Bulgaria. Historia naturalis bulgarica 9, 87-99.

Sims, R. W. 1955. The morphology of the head of the Hawfinch (Coccothraustes coccothraustes). Bulletin of the British Museum (Natural History) 2, 369-393.

van der Meij, M. A. 2004. A tough nut to crack: adaptations to seed cracking in finches. Unpublished thesis, Leiden University.

- . & Bout, R. G. 2004. Scaling of jaw muscle size and maximal bite force in finches. The Journal of Experimental Biology 207, 2745-2753.

Witmer, L. M. & Rose, K. D. 1991. Biomechanics of the jaw apparatus of the gigantic Eocene bird Diatryma: implications for diet and mode of life. Paleobiology 17, 95-120.

Comments

  1. #1 Procyon
    February 5, 2007

    Truly unique tetrapods..
    How about the Tuatara? Or perhaps Solenodon?

  2. #2 Christopher Taylor
    February 6, 2007

    I assume you mean without any known close relatives, not pleading special creation :-P. How about Leptosomus? Aptornis is probably about the oddest bird I’m aware of. Among mammals, Dromiciops is a bit of a phylogenetic oddball. I can’t think of many others – Ascaphus among frogs? If you wanted to broaden your field to very small clades, there’s certainly a few candidates among birds. Phaethon? Mesitornithidae? Leiopelma among frogs? Mystacinidae among mammals?

  3. #3 Poseidon
    February 6, 2007

    I’ve always wanted to go bird-watching. As usual, a splendid article with some great moments of discovery, and some thought-provoking comments on convergent evolution.

    There’s just one problem…

    These are not vampire bats.

  4. #4 Tommy Tyrberg
    February 6, 2007

    The Hawfinch is unusual in another sense. It is almost the only bird for which there is some evidence that it may have changed its ecology since the last glaciation. In faunas from the last glaciation it often occurs together with boreal taiga birds, not at all what you would expect today. However things may be a-changing again. In 1950 the Hawfinch was considered a rarity north of Scania, the southernmost province in Sweden. Now the northernmost breeding population is near Boden, less than 100 km south of the Arctic Circle!

    I think I will have a shot at the “unique tetrapod” challenge. I submit that the following tetrapods are unique morphologically and/or ecologically:

    The Kagu
    The Osprey
    The Hoatzin
    The Oilbird
    The Platypus
    The Polar Bear
    Humans

  5. #5 David Marjanovi?
    February 6, 2007

    I’ve actually spent some considerable time trying to find a tetrapod that is truly unique: without any close living or extinct relatives.

    How close is close for you?

    so you can look forward to the soon-to-appear ‘The science of Godzilla’ post (really).

    And then Giant Monster Gamera! Please! I only know it from its entry at http://www.stomptokyo.com, but that’s impressive enough. Excerpts:

    “The story of Giant Monster Gamera is that Gamera is a giant monster.”

    “Being a giant monster, Gamera is instinctively drawn to Tokyo.”

    Well, yeah, OK, if you want to treat the temnospondyls first… ;-)

  6. #6 Darren Naish
    February 6, 2007

    Thanks to all for comments and, it’s true, these aren’t vampire bats. Thanks for the info on changing ecology Tommy, I didn’t know that. Have you published on this subject?

    My point on ‘uniqueness’ is that I am hard pressed to think of a species that represents an isolated lineage, lacking closely related species.

    Tuataras fail: possibly two extant species [though this has recently been contested] and many, many fossil relatives, some of which are very similar to extant Sphenodon.

    Solenodons fail: there are several species, two of which are extant. Dromiciops fails as it has a host of close relatives from the Miocene; Ascaphus consists of three species and is not a singleton; Leptosomus is indeed a good ‘stand alone’, but it still has close Eocene relatives in the Plesiocathartes species; Phaethon consists of more than one species. The platypus fails, as there are several fossil species. There are also two fossil hoatzins. The Polar bear has of course some very very close relatives (and in fact polar bears can be argued to be a specialised population of Ursus arctos). Ospreys also fail as there are an additional two fossil species, plus a few others that appear to be distinct but remain unnamed. Mesites, leiopelmatids, mystacinids and humans are all groups consisting of some or lots of species.

    Both Aptornis and the kagu are good ones, but again neither is a single species on its own (as there are supposed to be two adzebills, and there is the extinct kagu Rhynochetus orarius). Finally, Tommy suggested the oilbird. This might fit the bill, though there are some fossil forms that may or may not be close relatives.

    Of course, this whole concept is entirely relative given that every taxon – no matter how phylogenetically remote – always has some other taxon that can be considered its closest relative. But the fact remains that it is very difficult to think of a single species that really is (i) monotypic, (ii) phylogenetically isolated, and (iii) without closely related living or fossil taxa. Moloch might fit the criteria, but there are suggestions that it is a species complex and not a single species.

  7. #7 Raymond
    February 7, 2007

    For shame! Everyone forgets the recently extinct bibymalagasy!

    http://en.wikipedia.org/wiki/Plesiorycteropus

    A singleton, no other fossil or living relatives known within its own clade, Bibymalagasia (MacPhee,1994).

  8. #8 Tommy Tyrberg
    February 7, 2007

    Formulated in those terms the uniqueness requirement is practically a self-defeating proposition. For a taxon to be truly unique and phylogenetically isolated means that it has to be an old lineage. An old lineage means that there is bound to be several chronospecies’ worth of change along the lineage even if there never was any branching. I can’t offhand think of any fossil tetrapod species with a known temporal range of more than about 15 million years. So what your conditions mean is essentially that the lineage also must not have any fossil record.

    Now that is a hard one. Most of the possible cases have already been mentioned. The bibymalagasy is of course a good one since Madagascar has essentially no tertiary fossil record. Among birds the cuckoo-roller (Leptosomus) and the oilbird probably come closest. Picathartes would be perfect if only there weren’t two species. The Hammerkop might fit, but i think there is one fossil species there. What else? Within Aves Sylviornis, Pedionomus, Dromas or Hypocolius might qualify.

  9. #9 Darren Naish
    February 7, 2007

    Raymond: I, for one, didn’t forget about Plesiorycteropus: it’s not a singleton, as there are two species. Incidentally, not everyone is sure that bibymalagasians represent a unique lineage. Szalay & Schrenk (1998) stated that “the possibility that it is a highly modified tubulidentate still lingers”.

    Tommy: you are totally right, my terms are “practically a self-defeating proposition”. My point is that just about everything has relatives of some sort – not that anyone (outside of creationism) ever doubted this, but an interesting point nonetheless. Some of the birds you cite are, however, further examples (Dromas, Hypocolius etc).

  10. #10 David Marjanovi?
    February 7, 2007

    Ascaphus consists of three species

    I thought two (A. truei, A. montanus)? When was the third discovered?

  11. #11 Christopher Taylor
    February 7, 2007

    Aptornis defossor is one of those “on again, off again” species – some authors accept it, others don’t. I believe there’s similar doubts about Sphenodon guntheri, but I don’t know if anything has appeared in print recently.
    A few other possibilities occurred to me – Lipotes might be one. It’s not closely related to the other river dolphins, and while a fossil lipotid has been named, the grounds for assigning it to Lipotidae are shaky IIRC. I had thought of Cladornis and Necrolestes earlier, but I didn’t mention them in my previous comment because I don’t know if they’re well enough known to really rule out the possiblity that they could turn out to be more ordinary once further evidence is discovered.

  12. #12 Nick Pharris
    February 11, 2007

    Great post as usual!
    I was just wondering, what’s your ref. for the re-splitting of Coccothraustes and Hesperiphona? All the field guides and on-line sites I’ve looked at still have C. vespertinus for the Evening Grosbeak.
    Also, the citation for the Arnaiz-Villena et al. 2001 paper should be Cellular and Molecular Life Sciences 58, 1159-1166.

  13. #13 Darren Naish
    February 11, 2007

    Thanks for the correction Nick. It’s true that a lot of texts still have the Evening grosbeak (and other species) as within Coccothraustes, but an equal number of authoritative sources have Coccothraustes as containing only C. coccothraustes (e.g., Clement et al‘s 1999 Finches & Sparrows). So far as I can tell from the literature, this latter point of view is the most widely accepted, but that doesn’t mean it’s universally accepted. Futhermore, some phylogenetic studies (e.g., Arnaiz-Villena et al. 2001) regard Coccothraustes and Hesperiphona as close relatives, in which case you might argue that the latter should be sunk into synonymy (again).

  14. #14 Brian
    August 23, 2008

    Eventhough I am awfully late in replying to this post, I can think of a few avian species that might be ‘unique’ in terms of there only being one known species and no known fossil ones.

    - sunbittern (Eurypyga)
    - rail-babbler (Eupetes)
    - Magellanic plover (Pluvianellus)
    - plains wanderer (Pedionomus)
    - ibisbill (Ibidorhynchus)
    - bearded reedling (Panurus)
    - palmchat (Dulus)
    - pink-tailed ‘bunting’(Urocynchramus)

    Would these fit the definition?

  15. #15 Graham King
    October 9, 2009

    Hawfinch: another bird I’ve never heard of (till Tet Zoo)!

    Re splitting of fruit pits (an impressive feat): is force, or pressure, really the key?

    A very narrow bill edge would magnify the pressure obtained for any given bill-closing force. There may be a critical narrowness which significantly aids splitting of the pit, by crack generation and propagation. We need some good data on fruit-pit materials science and likewise for birds’ bills (including rigidity/deformability, since I assume there must be some distortion under load). And how is the bill edge kept sharp for such use? What are the maximum pressures and forces that biological materials and tissues can withstand? Compression, tension, shear..
    Loads ( :-D ) of questions spring to mind..

    There is also the question of sudden shock/release of pressure, felt in skull/jaw- and neck-muscles/bill, as the pit (presumably) fails suddenly..
    And how does the bird manage to hold onto, or recapture, the disjected pieces? (I find flying debris to be a problem when using nutcrackers).

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