The Madagascan cuckoo-roller or Courol* Leptosomus discolor is a distinctive, large-headed, short-legged predatory bird that inhabits the forests of Madagascar and the Comores [adjacent photo of male Courol taken at Vakona in Madagascar; image courtesy of Mary Blanchard]. It’s superficially similar to true rollers (Coraciidae) and ground-rollers (Brachypteraciidae) but, unlike them, has semi-zygodactyl feet (though it has frequently very depicted inaccurately by artists who, in the absence of better information, have assumed that it’s anisodactyl, like true rollers). It’s often placed in its own ‘family’, properly termed Leptosomidae but often (incorrectly) referred to as Leptosomatidae (incidentally, there’s a nematode ‘family’ with this latter name).
* I’ve also seen it spelt Gourol.
The Courol also differs from true rollers and ground-rollers in that it hunts prey high in the forest canopy. It eats insects – including locusts, caterpillars and stick insects – but is particularly well known for preying on chameleons, of which there are an awful lot in Madagascar. It must sometimes eat a lot of caterpillars, as the stomach is often lined with caterpillar hairs (Burton 1984). It has powerful jaws (the temporal fossae are large, housing large jaw muscles, the jugals are stout, and the lacrimals form vertical braces against the jugals) and an extensively ossified palate (Cracraft 1971) [skull diagrams below from Cracraft (1971)]. As is the case in some other birds with extensively ossified palates (like hornbills), prey are grasped firmly between the jaws and beaten against a perch until subdued (Burton 1984). Leptosomus is also unusual in possessing slit-like nostrils that are located further toward the bill’s tip than is typical.
Male Courols have an iridescent green back, grey head and whitish underparts while females are mostly brown, with barred head plumage and spotted underparts. This sexual dimorphism is, again, very different from what’s seen in true rollers and ground-rollers: like most other birds conventionally grouped in ‘Coraciiformes’, true rollers and ground-rollers don’t exhibit obvious sexual dimorphism [image below of female or juvenile Courol by Frank Wouters, from wikipedia].
It’s usually thought that there’s just one species of Leptosomus, but three subspecies have been named: L. d. discolor of Madagascar and Mayotte Island, L. d. intermedius of Anjouan, and L. d. gracilis of Grand Comoro. L. d. gracilis is much smaller than the nominate form, has a faster and higher pitched call, and has a distinctly differentiated blue-grey throat and upper breast and pure white belly (in the other forms, the two colours merge into each other). As a result of these differences, some authors (e.g., Sinclair & Langrand 1998) consider the Grand Comoro population to represent a separate species: the Comoro cuckoo-roller L. gracilis.
As should be obvious by now, the Courol has often been considered close to ground-rollers and true rollers and classified with them in the ‘coraciiform’ group Coracii. However, when first described in 1783, Leptosomus was thought to be a cuckoo: it was originally named Cuculus discolor Herman, 1783 and it didn’t get its own genus name until Louis Jean Pierre Vieillot erected Leptosomus in 1816. Indeed, it does resemble a cuckoo, superficially at least. By 1865, Philip Sclater had argued that it wasn’t especially similar to cuckoos, and he suggested that it more resembled rollers and ground-rollers. Dissenting opinions were expressed by others (in 1872, Carl Sundevall regarded it as close to toucans, jacamars and honeyguides), but Sclater’s idea of roller affinities caught on and became widely regarded as correct.
Cracraft (1971) proposed that Leptosomus represented an early stage in roller evolution that pre-dated the evolution of sexual monomorphism (though he did express some doubt about the Courol’s precise affinities). He suggested that it evolved semi-zygodactyl feet from an anisodactyl ancestral roller because its large size and specialisation for arboreal life required improved perching abilities.
However, molecular and morphological evidence have shown pretty convincingly that the Courol’s affinities lie elsewhere, and that it isn’t a roller at all. Herremanns & Louette (1992) suggested a position close to cuckoos. Given the strong sexual dimorphism and barred, brown female plumage of the Courol, its semi-zygodactyl feet, strong, reinforced jaws, and habit of eating caterpillars, this proposed link – which, ironically, puts the Coural back where it started in 1783 – is intriguing (cuckoos have really interesting jaws, as do the possibly related turacos and hoatzins) [sexual dimorphism in the cuckoo Cuculus canorus shown here, pic from wikipedia]. Mayr (1998) included Leptosomus in a phylogenetic analysis with other ‘coraciiforms’, and found it to be outside of a clade that included all other putative members of this group. Furthermore, he suggested that it might group together with podargids (frogmouths), which seems odd but is at least consistent with some characters that are shared by the two (such as two powder down patches on the back). More recently, Mayr et al. (2003) found Leptosomus to group with frogmouths in the ‘nightbird’ + apodiform clade, Ericson et al. (2006) found Leptosomus to be outside of a land bird clade that includes owls, mousebirds, ‘core coraciiforms’, trogons and piciforms (woodpeckers and kin), and Hackett et al. (2008) found Leptosomus to be close to (but outside of) a clade that includes trogons, piciforms and ‘core coraciiforms’. Livezey & Zusi (2007) did find the Courol to be a roller, and to be the sister-taxon to ground-rollers. However, Mayr (2008a) argued that this was the result of incorrect character scoring whereby the Courol had wrongly been given the same characters states as ground-rollers [some possible positions for Leptosomus - depicted on a sort of very rough 'consensus' cladogram - are shown below].
The implication from these results is that Leptosomus is definitely not a ‘core coraciiform’ (and definitely not a roller) and that, while its precise affinities remain rather unclear, it represents some sort of ancient lineage that might lie within the region of the tree that includes ‘nightbirds’ and swifts, or piciforms and/or ‘core coraciiforms’. The problem with this statement is that some of these affinities are sometimes mutually incompatible: Hackett et al. (2008), for example, found frogmouths to be about as far removed as possible from piciforms and ‘core coraciiforms’*. On the other hand, if frogmouths, trogons, piciforms, ‘core coraciiforms’ and so on are all in the same region of the neoavian tree, then the results of the above-mentioned studies could all be more or less compatible. Do fossils provide any perspective on this subject?
* Hackett et al. (2008) recovered a neoavian clade that included flamingos and grebes (mirandornithines, if you like), tropicbirds, sandgrouse, mesites, pigeons, swifts and hummingbirds, and nightjars, frogmouths and so on. This clade formed the sister-group to all other neoavians in their analysis. This clade is extremely similar in content and position to the clade that Fain & Houde (2004) and Ericson et al. (2006) had earlier termed Metaves. Whether Metaves is real or not has become a really interesting question (Morgan-Richards et al. 2008)
Plesiocathartes from the Eocene and Oligocene of Europe and Eocene of North America – originally described as a New World vulture – seems to be a stem-leptosomid [P. kelleri Mayr, 2002 from Messel shown here; image from here]. In fact, it’s so similar overall to Leptosomus that Mayr (2008b) regarded the latter as a possible ‘living fossil’ (though Plesiocathartes does differ from Leptosomus in being anisodactyl).
The modern restriction of leptosomids to Madagascar may, therefore, be relictual following their extinction elsewhere, as the fossils show that these birds were once widespread across the Northern Hemisphere. If this is correct, why have leptosomids become so restricted? Were they out-competed by other roller-like birds? Were they unable to cope with the climatic changes of the Neogene? Once more, a poorly known and understudied bird is clearly deserving of a lot more attention.
For previous Tet Zoo articles on assorted land birds from this region of the cladogram (perhaps!) see…
- Sibley and Ahlquist’s ‘Tapestry’
- Ground hornbills: savannah-dwelling, avian pseudo-hominids
- The other ground hornbill
- A case of dead kingfishers
- Perhaps the weirdest chicks of all
Refs – -
Burton, P. J. K. 1984. Anatomy and evolution of the feeding apparatus in the avian orders Coraciiformes and Piciformes. Bulletin of the British Museum of Natural History (Zoology) 47, 331-443.
Cracraft, J. 1971. The relationships and evolution of the rollers: families Coraciidae, Brachypteraciidae, and Leptosomatidae. The Auk 88, 723-752.
Ericson, P. G. P., Anderson, C. L., Britton, T., Elzanowski, A., Johansson, U. S., Källersjö, M., Ohlson, J. I., Parsons, T. J., Zuccon, D., and Mayr, G. 2006. Diversification of Neoaves: integration of molecular sequence data and fossils. Biology Letters 22, 543-547.
Hackett, S. J., Kimball, R. T., Reddy, S., Bowie, R. C. K., Braun, E. L., Braun, M. J., Cjojnowski, J. L., Cox, W. A., Han, K.-L., Harshman, J., Huddleston, C. J., Marks, B., Miglia, K. J., Moore, W. S., Sheldon, F. H., Steadman, D. W., Witt, C. C. & Yuri, T. 2008. A phylogenomic study of birds reveals their evolutionary history. Science 320, 1763-1768.
Herremanns, M. & Louette, M. 1992. Sexual dimorphism in the juvenile plumage of the Coural Leptosomus discolor and considerations on its affinities. Bulletin of the British Ornithologists’ Club 112, 182-185.
Livezey, B. C. & Zusi, R. L. 2007. Higher-order phylogeny of modern birds (Theropoda, Aves: Neornithes) based on comparative anatomy. II. Analysis and discussion. Zoological Journal of the Linnean Society 149, 1-95.
Mayr, G. 1998. “Coraciiforme” und “piciforme” Kleinvögel aus dem Mittel-Eozän der Grube Messel (Hessen, Deutsch-land). Courier Forschungsinstitut Senckenberg 205, 1-101.
- . 2008a. Avian higher- level phylogeny: well-supported clades and what we can learn from a phylogenetic analysis of 2954 morphological characters. Journal of Zoological Systematics and Evolutionary Research 46, 63-72.
- . 2008b. The Madagascan “Cuckoo-roller” (Aves: Leptosomidae) is not a roller — notes on the phylogenetic affinities and evolutionary history of a “living fossil”. Acta Ornithologica 43, 226-230.
- ., Manegold, A. & Johansson, U. S. 2003. Monophyletic groups within ‘higher land birds’ – comparison of morphological and molecular data. Journal of Zoological and Systematic Evolutionary Research 41, 233-248.
Morgan-Richards, M., Trewick, S. A., Bartosch-Härlid, A., Kardailsky, O., Phillips, M. J., McLenachan, P. A. & Penny, D. 2008. Bird evolution: testing the Metaves clade with six new mitochondrial genomes. BMC Evolutionary Biology 2008, 8:20 doi:10.1186/1471-2148-8-20
Sinclair, I. & Langrand, O. 1998. Birds of the Indian Ocean Islands: Madagascar, Mauritius, Réunion, Rodrigues, Seychelles and the Comoros. Struik, Cape Town.