September 3, 2011

Obscure, extravagant tropical crows

This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American

The word ‘crow’ typically conjures up an image of a reasonable large, typically black, typically unadorned passerine bird. Crows of this kind occur just about worldwide with the exception of South America and Antarctica – they’re very successful birds. But far less well known is that there is also a really interesting assortment of brightly coloured, often fairly extravagant, tropical corvids. Sure, everyone really interested in birds knows about the species concerned, but this article isn’t necessarily written for those people.

Here I want to focus very briefly on just three of the world’s obscure, extravagant tropical crows. All are American. Being mid-sized (for crows), crested, fairly long-tailed and with non-black plumage, they’re popularly known as jays. This is a vernacular term, not a taxonomic one.

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Plush-crested, Curl-crested and Tufted jays

We begin with the rather poorly known Plush-crested jay or Plush-capped jay Cyanocorax chrysops of south-eastern Brazil as well as north-eastern Argentina, Bolivia, Uruguay and Paraguay. It’s named for its dark, velvety head crest. Its violet-blue upperparts contrast with its creamy-white underparts. Like most forest-dwelling, tropical crows, its wings are very broad and its tail is long. The Plush-crested jay is best known for foraging in the canopies of rainforests, though it also descends to the ground, forages at intermediate levels in the forest, and can sometimes be found in forested islands on the pampas and in other wooded habitats. It moves around in small groups, sometimes associating with Purplish jays C. cyanomelas and Azure jays C. caeruleus (Madge & Burn 1999). It’s omnivorous, eating fruits, berries, bird’s eggs, arthropods and other items.

As is so often the case with bird species, some Plush-crested jay populations differ enough in appearance to perhaps warrant the naming of subspecies. C. c. tucumanus of north-eastern Argentina is apparently larger than the nominate C. c. chrysops while C. c. diesingii has a longer, more upright crest than C. c. chrysops and a somewhat different pattern of facial markings. A form named for a single specimen – C. c. interpositus – might be a hybrid between a Plush-crested jay and White-naped jay C. cyanopogon (Goodwin 1986).

Another South American jay with an unusual feathery crest is the highly distinctive (but also fairly poorly known) Curl-crested jay C. cristatellus. It inhabits the tablelands of central Brazil and adjacent north-east Paraguay and is often imagined to be limited to a kind of woodland called ‘cerrado’. Here, short, gnarled trees grow within a savannah-style grassland. However, there’s at least one observation of a Curl-crested jay in dense riparian forest (Hardy 1969). Again, it moves in flocks: it’s almost certainly a social breeder but nothing much is known of its social behaviour or breeding biology (Goodwin 1986). Its crest consists of long, erect, stiff, curved plumes that grow amid shorter bristles. It possesses a wholly black ‘hood’ and, elsewhere on its body, a combination of pure white and violet-blue plumage.

One of the most striking and charismatic of tropical crows is the Tufted jay or Painted jay C. dickeyi of the Sierra Madre Occidental in western Mexico [adjacent photo from BirdQuest]. An inhabitant of both deciduous and evergreen woodlands in mountainous regions, it’s absolutely unmistakeable, with a black, fan-shaped crest of stiff bristles, white nape and white terminal half of tail. Given its remarkable appearance, it’s surprising that it was only discovered in 1934 (and named the following year).

Like other Cyanocorax jays, the Tufted jay is a generalist, eating fruits, berries, acorns, arthropods and occasionally bird’s eggs and even nestlings. It reportedly tears open bromeliads, though whether this is because it’s searching for animal prey or for stored food caches isn’t entirely clear (Goodwin 1986). Flocks consists of between four and 16 birds, with only a single pair nesting at a time and the rest of the flock helping by collecting nesting material as well as food for the incubating female and her chicks. It has an extremely diverse vocabulary, indulges in a great deal of mimicry of other bird species and has been reported to make all kinds of chattering noises as well as metallic, clicking and hooting calls. Its restricted range and social breeding make it vulnerable to habitat destruction and it has sometimes been referred to as “distinctly uncommon” (Madge & Burn 1999). “Intensive collecting” has also led to its local extinction in some places (Goodwin 1986). I wonder whether this ‘collecting’ was for taxidermy specimens or live ones destined for captivity.

A tree for New World jays

All three species covered here are members of Cyanocorax, and the Plush-crested and Tufted jay at least may be very close relatives within this clade. All Cyanocorax jays have fairly prominent ‘frontal tufts’ of some sort, are generally heavily built, and are mostly lowland crows with a co-operative breeding habit. Exactly how these striking Neotropical corvids are related to other members of the crow family, however, is open to debate, and various different positions have been proposed.

The Cyanocorax species share blue feathering, frontal crests and various voice characteristics with Cyanocitta (the Blue jay and Steller’s jay), and they’ve typically been linked with the scrub jays (Aphelocoma), the Andean Cyanoluca jays, the Central American Brown jay Psilorhinus morio, and the magpie-jays Calocitta, many of which are also bluish and crested. Together, these six genera form an assemblage known as the New World jays; the distinctive Piñon jay Gymnorhinus cyanocephalus is likely also a member of the group, but it’s regarded by some authors as closer to such Old World corvids as nutcrackers. All New World jays share a distinctive and specialised lower jaw morphology where an extra convexity near the jaw joint, a knob on the quadrate bone and a ‘chisel-shaped’ mandible tip form a functional complex that apparently allows them to exert extra force when breaking into hard objects with the jaw tips. This set of features was termed the buttress complex by Zusi (1987) and it isn’t seen in other corvids.

Because the majority of corvid lineages are Old World denizens, it has generally been thought that New World jays descend from a jay-like corvid that invaded the Americas via Beringia. The Perisoreus, which are ancestrally Eurasian but with one American species [the Siberian jay P. infaustus is illustrated below] , have been argued by some authors to be the most likely near-ancestors for New World jays, and indeed Espinosa de los Monteros & Cracraft (1997) recovered Perisoreus as the sister-taxon to the New World jay clade.

If this phylogenetic hypothesis is correct, a Perisoreus-like jay presumably arrived in North America during the Early Miocene or so, its descendants spreading south and radiating in South American after the formation of the Panamanian isthmus. The idea of a Miocene invasion in part comes from Brodkorb’s (1972) description of the Late Miocene jay Miocitta galbreathi from Colorado. It shares various similarities with extant New World jays.

In an effort to resolve affinities within the New World jay clade, Espinosa de los Monteros & Cracraft (1997) examined cytochrome b and morphological data. They found Cyanocorax to form a clade with the magpie-jays. The Cyanoluca jays formed the sister-group to all other New World jays. Cibois & Pasquet (1999) analysed mtDNA from a diversity of crows and found Cyanocorax to group together with Cyanocitta (the Blue jay and Steller’s jay). However, this Cyanocorax + Cyanocitta clade was the sister-group to the rest of Corvidae with the exception of choughs (they occupied an even more distant position relative to the remainder of Corvidae), and it had no close affinity with Perisoreus or indeed any other jay-like corvids. This is a peculiar result as it means that New World jays diverged comparatively early on in corvid evolution; it also means that they have no close affinity with any of the Old World jays. You might like to wonder what the New World jay ancestor looked like in this scenario: they’re surrounded by choughs on the one hand, and the large clade that contains nutcrackers and true crows, and magpies and Old World jays, on the other.

Saunders & Edwards (2000) found Cyanocorax to form a clade with the Brown jay and the magpie-jays [Brown jay in adjacent photo; image from BIRDseeN]. In this study, Cyanocitta formed a clade with the scrub jays. The idea that the Brown jay might be close to Cyanocorax isn’t as peculiar as it might seem – despite its brownish plumage it has sometimes even been classified as a species of Cyanocorax and at other times said to be especially close to Cyanocitta. In fact, there’s even an alleged Cyanocitta x Psilorhinus hybrid on record (Pitelka et al. 1956). An interesting peculiarity of the Brown jay is the bare, inflatable patch on its chest, purported to aid in temperature control. Incidentally, the phylogeny recovered by Saunders & Edwards (2000) suggests that co-operative breeding was likely primitive for the whole of the New World jay clade, but that it has been lost by Cyanocitta and in some taxa within Aphelocoma. As goes the origins of the New World jay clade, Saunders & Edwards (2000) again found Perisoreus to be the sister-group to the whole clade, and their results thus support the idea of a single invasion across Beringia.

Ericson et al. (2005) compiled phylogenies using data from several different genes. They mostly found Cyanocorax to group together with the magpie-jays – sometimes with the Brown jay as closer to the magpie-jays than to Cyanocorax. But, like Cibois & Pasquet (1999), they didn’t find Perisoreus to be at all close to the New World jays. Rather, they tended to recover a polytomy where New World jays, true crows and nutcrackers and Garrulus jays, magpies, and Perisoreus jays all diverged rapidly from an Old World ancestor. In many of these clades, the most basal positions are occupied by south-east Asian taxa. It seems that, while many of the crow groups radiated extensively in Eurasia from this south-east Asian area of origin, several moved to the Americas, with the New World jay clade apparently doing this earliest and most successfully.

I’ll definitely be coming back to corvid diversity, phylogeny and history some time. So much for a brief article on just those three species.

For previous Tet Zoo articles on crows and other ‘core corvoids’, please see...

And for more on passerines of all kinds, check out...

Refs - -

Brodkorb, P. 1972. Neogene fossil jays from the Great Plains. The Condor 74, 347-349.

Cibois, A., & Pasquet, E. (2008). Molecular analysis off the phylogeny off 11 genera off the Corvidae Ibis, 141 (2), 297-306 DOI: 10.1111/j.1474-919X.1999.tb07552.x

Ericson, P. G. P., Jansén, A.-L., Johansson, U. S. & Ekman, J. 2005. Inter-generic relationships of the crows, jays, magpies and allied groups (Aves: Corvidae) based on nucleotide sequence data. Journal of Avian Biology 36, 222-234.

Goodwin, D. 1986. Crows of the World. Trustees of the British Museum (Natural History), London.

Hardy, J. W. 1969. A taxonomic revision of the New World jays. Condor 71, 360-375.

Madge, S. & Burn, H. 1999. Crows & Jays. Christopher Helm, London.

Pitelka, F. A., Selander, R. K. & Del Torro, M. A. 1956. A hybrid jay from Chiapas, Mexico. Condor 58, 98-106.

Saunders, M. A. & Edwards, S. V. 2000. Dynamics and phylogenetic implications of mtDNA control region sequences in New World jays (Aves: Corvidae). Journal of Molecular Evolution 51, 97-109.

Zusi, R. L. 1987. A feeding adaptation of the jaw articulation in New World jays (Corvidae). The Auk 104, 665-680.