Orioles: The Genuine Article

Eurasian golden oriole Oriolus oriolus, copyright Crusier.

It is widely appreciated that the British during the age of exploration were probably not the most imaginative of baptisers. Thanks to their tendency to label the fauna of foreign lands with the names of familiar animals back home, we are regularly confronted with warblers that aren't warblers, cod that aren't cod, monkeys that aren't monkeys. And for years, many an American has laboured under the mistaken impression that they know what an oriole is. This post is about the real orioles.

The Oriolidae are a family of birds found mostly in the tropics of the Old World, from Africa to Australia. Only a few species in the family are known from temperate climes. One of these is the original oriole, the European Oriolus oriolus, which migrates between sub-Saharan Africa and its breeding range in Europe and central Asia. The name 'oriole' is derived from the Latin word for 'golden', and there is no question of this being an appropriate name for the European bird. The male's plumage is almost entirely golden yellow, with the wings being black. As is commonly the way with birds, the females are less dramatic, being predominantly green. Despite the males' bright coloration, though, orioles are by all accounts fairly retiring birds, usually remaining secluded in the tree canopy, where they seek out fruit and small insects.

Black-and-crimson oriole Oriolus cruentus malayanus, copyright Christopher Hill.

The majority of the about thirty remaining species of Oriolus are also some combination of gold, green and/or black, but there are notable exceptions. A clade of Australo-Papuan and Moluccan species, identified by Jønsson et al. (2010) as the sister group to the other Oriolus species, contains relatively dull brown or greenish species. The Moluccan species in this clade bear a strong resemblance to friarbirds, a group of honeyeaters found in the same region, to the extent that the black-eared oriole Oriolus bouroensis was first described as a friarbird. It has been suggested that this represents a case of mimicry with the retiring orioles gaining a degree of protection from their resemblance to the aggressive friarbirds (Dickinson 2004). Another Asian clade identified by Jønsson et al. (2010) includes mostly red and black species. It also includes the silver oriole Oriolus mellianus in which the red coloration has been mostly lost, so that it is mostly silver-white with a black head and wings.

Male and female Australasian figbirds Sphecotheres vieilloti, copyright Jim Bendon.

Also included in the Oriolidae are the three species of figbird in the genus Sphecotheres, found in the Australo-Papuan region. The figbirds, as their name suggests, have a higher proportion of fruit in their diet than orioles. They are also more sociable, living in small flocks. Figbirds are distinguished from orioles by the presence of patches of bright red bare skin around their eyes; they are otherwise a dull greenish colour. Recent studies have also indicated oriolid affinities for Pitohui, a genus of two red and black birds, the hooded pitohui P. dichrous and variable pitohui P. kirhocephalus, found in New Guinea. Previous authors have included six species in Pitohui, but phylogenetic studies have revealed that the genus in the broad sense is widely polyphyletic, with the remaining species belonging to different bird families. The red and black markings of the 'pitohuis' are a case of aposematic coloration, advertising that its bearer is toxic. The pitohuis contain batrachotoxins in their skin and feathers, a similar substance to that found in the poison-arrow frogs of South America. Contrary to what you may read elsewhere, the pitohuis were not the first known case of toxicity in birds, though it was one of the most definite ones. It has been known since ancient times that migratory quail Coturnix coturnix are toxic at certain points on their migratory route: the biblical book of Numbers describes a case of mass poisoning suffered by the Israelites during the exodus. Other examples of birds that are at least seasonally toxic include the spur-winged goose Plectropterus gambensis and the bronzewing pigeons of the genus Phaps (a brief review of bird toxicity is provided by Bartram & Boland, 2001). As far as is known, all cases of toxicity in birds result from feeding on something containing the relevant toxic substance (probably beetles, in the case of pitohuis) which is then sequestered by the bird.

Mounted North Island piopio Turnagra tanagra, copyright Te Papa.

The Australo-Papuan distribution of these two genera, together with the basal position of the Australo-Papuan species in the genus Oriolus, suggests that the family originated in this area before crossing the Wallace Line to diversify in Eurasia and Africa (Jønsson et al. 2010). An Australo-Papuan origin for the orioles also correlates with the presence of a fossil oriolid, Longmornis robustirostrata, in the early Miocene Riversleigh deposit of Australia (Boles 1999). It also correlates with the recent identification as oriolids of the now extinct New Zealand piopios of the genus Turnagra (Zuccon & Ericson 2012). The piopios were two species (the South Island piopio Turnagra capensis and the North Island T. tanagra) of mostly brown songbirds, also commonly known as the New Zealand thrushes. Their song was described as being amongst the most beautiful of any New Zealand bird, both complex and with a propensity towards mimicking other birds. Though seemingly common at the time of European settlement, they declined rapidly and probably became extinct around the start of the 20th Century. The affinities of the piopios were long contentious, with leading suggestions including a relationship with the whistlers of the Pachycephalidae, or with the bowerbirds of the Ptilonorhynchidae. Zuccon & Ericson (2012) marshalled an array of molecular, morphological and behavioural evidence in favour of a relationship with the orioles, though this stands in contrast with an earlier molecular study that supported the bowerbird hypothesis (Zuccon & Ericson noted that the cytochrome b sequence reported in the earlier study did not correspond with the one they found themselves, and suggested that it may have been the result of contamination). The dull coloration of the piopios compared to other orioles was explained by Zuccon & Ericson as a loss of sexual dimorphism, but this may have been unnecessary: they seem to have overlooked the similarly dull coloration of a number of other basal oriolids. The fact that the piopios were described as more terrestrial than the other oriolids is also not unusual in the New Zealand context. After all, the New Zealand bird fauna is famed for its tendency towards terrestrialisation (it even included a terrestrial owlet-nightjar!) In an environment where the main threat came from above in the form of birds of prey, the ground must have seemed like a welcoming place to be.

REFERENCES

Bartram, S., & W. Boland. 2001. Chemistry and ecology of toxic birds. ChemBioChem 2: 809–811.

Boles, W. E. 1999. A new songbird (Aves: Passeriformes: Oriolidae) from the Miocene of Riversleigh, northwestern Queensland, Australia. Alcheringa 23: 51-56.

Dickinson, E. C. 2004. Systematic notes on Asian birds. 42. A preliminary review of the Oriolidae. Zool. Verh. Leiden 350: 47-63.

Jønsson, K. A., R. C. K. Bowie, R. G. Moyle, M. Irestedt, L. Christidis, J. A. Norman & J. Fjeldsa. 2010. Phylogeny and biogeography of Oriolidae (Aves: Passeriformes). Ecography 33: 232–241.

Zuccon, D., & P. G. P. Ericson. 2012. Molecular and morphological evidences place the extinct New Zealand endemic Turnagra capensis in the Oriolidae. Molecular Phylogenetics and Evolution 62: 414–426.