Finches in Drag

Green-headed tanager Tangara seledon, copyright Dario Sanches.

In many parts of tropical South America, it is common to see small flocks of brightly coloured small birds foraging among vegetation, plucking off berries or hunting for insects. In many cases, these flocks may contain individuals of multiple or even several species. These are the tanagers, one of the Neotropical region's most characteristic bird families.

Tanagers are members of the bird clade known as the nine-primaried songbirds (so-called because their wings have nine functional primary feathers rather than the ten of other songbirds) that also includes the finches, buntings and cardinals. The largest genus of tanagers, and indeed one of the larger genera of birds in general, is Tangara. This genus includes about fifty species found in various parts of the neotropics. In their overall structure, they are fairly uniform: small, sturdy birds with a stout, moderate-length bill and an average-length tail (Hilty 2011). In other words, they have a fairly unremarkable, finchy-type appearance. In colour and patterning, however, they are considerably more varied, to the extent that I am at a loss to know where to begin. There are species of a rich, deep blue and of a bright, emerald green. There are species with bold, contrasting patterns of blues, blacks, greens or golds; there are species of a solid, uniform brilliance. There are species with caps or chests of orange or black. There are even a few, such as the plain-coloured tanager Tangara inornata, that eschew the gaudy pigments of their congeners entirely in favour of more restrained patterns of greys and beiges. In many species, males and females show little or no difference in appearance; however, in the black-capped group (including species such as the black-capped tanager T. heinei), the males have contrasting patterns of black and blue or yellow whereas the females are largely green and grey.

Golden tanager Tangara arthus, copyright Alejandro Bayer Tamayo.

As noted above, tanagers feed on a mixed diet of fruit and insects. The fruit part is dominated by small berries that they can either swallow whole or mash with their bills before swallowing them piecemeal. Studies on the mixed-species flocks formed by Tangara species have found that while different species show very little variation in how they obtain the fruit component of their diet, they usually show very distinct specialisations in how they forage for insects. Some hunt for insects along branches, others prefer to look on leaves. Branch-hunting species may differ in the thickness and density of branches preferred, or in the mode of searching employed. For instance, the golden tanager T. arthus and flame-faced tanager T. parzudakii can both be found foraging on moss-covered branches, but the flame-faced tanager usually catches insects by probing directly into the moss whereas the golden tanager usually either focuses on the moss-free sections or catches insects sitting on the moss surface without probing. A few species catch insects aerially, making short sallies from a perch.

Blue-grey tanager Thraupis episcopus, indicated by phylogenetic analysis as a species of Tangara, copyright Mdf.

Somewhat unexpectedly for a genus of this size and diversity in a group as taxonomically challenging as the tanagers, molecular phylogenetic studies have largely corroborated Tangara's monophyly. They have also supported the monophyly of most of the species groups recognised within the genus of the basis of similarities in plumage patterns (Sedano & Burns 2010). The only exception has been the discovery that many of the species previously included in the genus Thraupis form a clade nested within Tangara, leading to the suggestion that these two genera should be synonymised (apart from in informal discussions online, I'm not aware of anyone suggesting the alternative that Tangara be split). The 'Thraupis' species are larger and plainer in coloration than most other Tangara species. A few taxonomists have also suggested that the colourful green tanagers of the genus Chlorochrysa should be included in Tangara, but this relationship has not been supported by molecular data. Chlorochrysa species are glossier than the often more matt-coloured Tangara, and they have an acrobatic mode of foraging involving postures such as regularly hanging upside-down that differ from any Tangara species.

REFERENCES

Hilty, S. L. 2011. Family Thraupidae (tanagers). In: del Hoyo, J., A. Elliott & D. Christie. Handbook of the Birds of the World vol. 16. Tanagers to New World Blackbirds pp. 46–329. Lynx Edicions: Barcelona.

Sedano, R. E., & K. J. Burns. 2010. Are the northern Andes a species pump for Neotropical birds? Phylogenetics and biogeography of a clade of Neotropical tanagers (Aves: Thraupini). Journal of Biogeography 37: 325–343.

The Hawaiian Honeycreepers: Diversity in Danger

'Apapane Himatione sanguinea, copyright Peter LaTourette.

In 1938, avian malaria was discovered to have affected pigeons in the city of Honolulu (Amadon 1950). This might have seemed like a minor detail—except among breeders, pigeons do not normally elicit much concern from the average person—but it was to prove a disaster. From the pigeons, the disease spread into native birdlife of the Hawaiian archipelago and wreaked havoc. Many species living at lower elevations were wiped out, unable to withstand the disease's effects. Others were forced into remnant populations above an elevation of 1500m, where the disease's mosquito vectors were unable to survive.

Among the malaria's victims were several species of the Hawaiian honeycreepers, a group of small birds unique to the archipelago. The honeycreepers have become recognised as one of the classic examples of an island adaptive radiation, like the Madagascan vangas or the Galapagos finches. From the original colonisation of the archipelago by what was probably a fairly generalised finch-like bird, perhaps some five or six million years ago (Lerner et al. 2011), the Drepanidini have diversified into a disparate array of seed-eaters, insectivores and nectar-feeders. Some have evolved massive reinforced bills to crush the seeds of local trees such as koa or naio. Other have long slender bills that they use to reach into the depths of flowers or prise insect larvae from holes in bark. Currently, about fifty species of honeycreeper are known to have been present in the Hawaiian archipelago prior to human settlement; new ones continue to be described from fossil or subfossil remains. Sadly, due to factors such as habitat loss, competition with and predation by introduced fauna, and diseases such as the aforementioned malaria, only about twenty species remain alive today and many of those are critically endangered.

Maui 'alauahio Paroreomyza montana, copyright Markus Lagerqvist.

Older references will refer to the Hawaiian honeycreepers as their own family, the Drepanididae, due as much to long-standing uncertainty about their relationships to other birds as to their own distinctiveness. Many authors, such as Amadon (1950), argued for a connection between the honeycreepers and the South American flowerpiercers of the tanager family, believing that the nectar-feeders among the Drepanididae were closer in appearance to the group's original ancestor. However, recent studies, both molecular and morphological, have been unified in supporting a connection between the honeycreepers and the finches of the Fringillidae, leading to the demotion of the 'family' Drepanididae to a 'tribe' Drepanidini of the fringillids. In his original studies on the honeycreepers, Perkins recognised two subgroups: the 'melanodrepanines' were mostly nectar-feeders and were largely black and/or red in coloration, whereas the 'chlorodrepanines' were mostly seed-eaters or insectivores and usually yellow or greenish. Recent studies have supported the 'melanodrepanines' as a clade but identified the 'chlorodrepanines' as paraphyletic.

Po'o-uli Melamprosops phaeosoma, copyright Paul Baker.

One unusual feature of many Drepanidini is that they carry a distinctive scent that has been referred to as the 'drepanidine odour' (this site describes it as a sweet, musty smell). Two primarily insectivorous genera, the po'o-uli Melamprosops phaeosoma and the ʻalauahios Paroreomyza, lack this 'drepanidine odour', and on the basis of this and a couple of other points it has been questioned whether they are properly assigned to the Drepanidini. However, the osteological analysis of Drepanidini by James (2004) confirmed their position as drepanidines, a result that has since been corroborated by molecular analyses. It seems likely that Melamprosops and Paroreomyza are basal drepanidines outside an 'odoriferous' clade (Pratt 2014). Together with the akikiki Oreomystis bairdi, these species form a basal grade of generalist feeders with fairly slender bills. It is possible that the akikiki and the Maui ʻalauahio Paroreomyza montana are the only members of this grade surviving.

Laysan finches Telespiza cantans, copyright S. Plentovich.

The next clade of drepanidines to diverge in molecular phylogenies includes the Hawaiian finches, an assemblage of often seed- or fruit-eating species with thick, strong bills (Pratt 2014). James' (2004) osteological analysis did not resolve the finches as a single clade, instead intermingling them with the aforementioned grade. Again, the finches have been hard hit by extinction, with the only survivors being the palila Loxioides bailleui, the Laysan finch Telespiza cantans and the Nihoa finch T. ultima. Amadon (1950) noted that the Kona grosbeak Chloridops kona was extremely rare even when first discovered in the late 1800s, being restricted to an area of only 'a few square miles' in the Kona district of Hawai'i. The grosbeaks of the genus Chloridops and the koa finches of the genus Rhodacanthis had particularly strongly developed bills for cracking seeds, looking almost parrot-like in the case of Chloridops (James 2004). Of uncertain relationships to the finches are two unusual extinct species, the 'o'u Psittirostra psittacea and the Lanai hookbill Dysmorodrepanis munroi. The 'o'u was a fruit-eating, large-billed bird that was once widespread on the main islands of the Hawaiian archipelago (in contrast to most other honeycreeper species, which were mostly restricted to a single island). It was last definitely recorded in 1989 and continued survival is considered unlikely. The Lanai hookbill was a particularly bizarre species in which the mandible and maxilla were curved toward each other, so that the base of the bill gaped open even when the beak was closed. The single known specimen is unusual enough that Amadon (1950) did not accept that it represented an actual species, expressing the opinion that it was probably a deformed 'o'u specimen; current authors accept it as a good species.

Crested honeycreeper Palmeria dolei, from the US Geological Survey.

As noted above, the nectar-feeding 'melanodrepanines' form a well-supported clade including three surviving species: the 'i'iwi Drepanis coccinea, the crested honeycreeper or akohekohe Palmeria dolei and the 'apapane Himatione sanguinea, the last of which is one of the more abundant living honeycreepers. The melanodrepanines have slender bills, which in the species of Drepanis (the 'i'iwi and two extinct species of mamo) are long and downcurved. Also probably belonging to the melanodrepanines is the extinct ʻula-ʻai-hawane Ciridops anna, which shared their black and red plumage despite being a fruit- rather than a nectar-feeder.

Kaua'i 'akialoa Akialoa procerus (front) and Kaua'i nukupuu Hemignathus hanapepe (rear), from Keulemans (1890).

The final group of drepanidines to be considered here is also the largest, and contains the most surviving species: the 'amakihis of the genus Chlorodrepanis, the 'akepas Loxops, and related taxa. These are slender-billed insectivorous forms with the more generalist species being similar in appearance to the basal genera Paroreomyza and Oreomystis. Indeed, the classification of drepanidines by Amadon (1950), which was decidedly more lumpy than the current norm, subsumed the latter two genera in an expanded Loxops. Possibly related to this group are the extinct 'akialoas of the genus (wait for it...) Akialoa, which had an extremely long down-curved bill. Two other genera of this group, Hemignathus (including the ʻakiapolaʻau Hemignathus wilsoni) and the Maui parrotbill Pseudonestor xanthophrys, are unique among passerines in having a maxilla that significantly overhangs the much shorter mandible. The Maui parrotbill, despite being primarily an insectivore, has a heavier bill somewhat reminiscent of the finch group, and James' (2004) morphological analysis (which was primarily based on skull features) associated it with Psittirostra and Dysmorodrepanis rather than with Hemignathus; the latter association, however, is supported by molecular analyses, indicating a single origin for the unequal bills.

The loss of this remarkable radiation can be regarded as nothing short of a tragedy. Only two species of Hawaiian honeycreeper are currently regarded as not threatened (as given in the IUCN listings at Wikipedia), the 'apapane and the common 'amakihi Chlorodrepanis virens. Even these species could become endangered as a warming climate allows malaria-carrying mosquitoes to encroach further on their highland refuges. And something truly wonderful could be lost from the world.

REFERENCES

Amadon, D. 1950. The Hawaiian honeycreepers (Aves, Drepaniidae). Bulletin of the American Museum of Natural History 92 (4): 151–262.

James, H. F. 2004. The osteology and phylogeny of the Hawaiian finch radiation (Fringillidae: Drepanidini), including extinct taxa. Zoological Journal of the Linnean Society 141: 207–255.

Lerner, H. R. L., M. Meyer, H. F. James, M. Hofreiter & R. C. Fleischer. 2011. Multilocus resolution of phylogeny and timescale in the extant adaptive radiation of Hawaiian honeycreepers. Current Biology 21: 1838–1844.

Pratt, H. D. 2014. A consensus taxonomy for the Hawaiian honeycreepers. Occasional Papers of the Museum of Natural Science, Louisiana State University 85: 1–20.

The Parulidae: Not-warblers, Not-ovenbirds and Not-redstarts

Black-crested warbler Myiothlypis nigrocristata, photographed by Mikko Pyhälä.

There is no denying the current status of English as the de facto lingua franca of the world*. And yet, I feel that a complaint must be laid at the feet of the Brits: they're a bit unimaginative when it comes to animal names. Many a British explorer, upon being presented with some hitherto unfamiliar product of the natural world, proceeded to label it with the name of whatever inhabitant of his native Europe he felt bore some vague resemblance. And hence, even today, there are significant groups of animals such as the Parulidae that are almost without a vernacular name to genuinely call their own.

*The potential irony of this sentence is not lost on me.

The Parulidae are a family of birds found throughout the Americas, though in the northern United States and Canada they are represented by migratory species that retreat further south in the cold months. Many of the migratory species have males with brightly coloured breeding plumage and are consequently idolised by North American bird watchers; non-migratory species, on the other hand, tend to have similarly subdued males and females (Update: see comments below). Members of the Parulidae are generally referred to as 'warblers' or 'wood warblers', despite not being at all closely related to the European warblers. Instead, parulids are members of the 'nine-primaried oscines', the passerine clade that also includes such birds as finches, buntings, sparrows, cardinals and tanagers. Within the nine-primaried oscines, parulids are closely related to the Icteridae, another American clade containing its fair share of representatives doomed to masquerade under stolen names (Barker et al. 2013).

Ovenbird Seiurus aurocapilla on its nest, photographed by M. C. Donald.

Though the nine-primaried oscines as a whole are fairly stable in their membership, recent years have seen a fair bit of shuffling back and forth between the clade's constituent families. As a result of this shuffling, the name 'Parulidae' has come to be associated with a core clade that excludes a number of more uncertainly placed taxa previously included in the family, such as the Central American wrenthrush Zeledonia coronata. A recent comprehensive study of the molecular phylogeny of the core parulids by Lovette et al. (2010) also resulted in a proposed shifting of many generic boundaries within the clade. According to Lovette et al., the basalmost member of the Parulidae is the ovenbird Seiurus aurocapilla, a migratory but monomorphic, relatively large parulid of North and Central America. Just to confuse matters, the name 'ovenbird' has also been used for an unrelated group of South American birds of the genus Furnarius. To be charitable, this is not a case of inappropriate name-saking, but refers to the construction by both groups of domed nests resembling an old earthernware oven. The next member of the parulids to split off was the worm-eating warbler Helmitheros vermivorus, a relatively long-billed species that migrates between the eastern United States and Central America.

Swainson's warbler Limnothlypis swainsonii, photographed by Greg Lavaty.

Next comes a clade of eight species classified in the genera Parkesia, Vermivora, Mniotilta, Limnothlypis and Protonotaria. The black-and-white warbler Mniotilta varia is noted for its distinctive feeding behaviour: it crawls along branches like a nuthatch or creeper, gleaning insects from the bark. The prothonotary warbler Protonotaria citrea is a bright yellow species that Kurt Vonnegut devoted some time to in Jailbird: "The song of a prothonotary warbler is notoriously monotonous, as I am the first to admit...Still—they are capable of expressing heartbreak—within strict limits, of course" (I personally feel the same about skylarks). The waterthrushes of the genus Parkesia are larger, terrestrially-feeding species.

Chestnut-sided warbler Setophaga pensylvanica, photographed by Cephas.
Other North American species are placed by Lovette et al. in the larger genera Geothlypis, Oreothlypis and Setophaga. The last genus contains the species previously included in Dendroica, but the recognition that the American redstart Setophaga ruticilla (again, no relation to the European redstart) is nested within Dendroica leads to the use of the older name. These genera include some of the most colorful parulids. The remaining genera Myiothlypis, Basileuterus, Cardellina and Myioborus form a mostly Neotropical clade. Myioborus species are also known as redstarts, presumably by comparison with the European birds as not one of them actually possesses a red tail. The name 'whitestart' has supposedly been proposed instead, but the only time that name appears to see use is when it is referred to by someone explaining why they are not using it...

REFERENCES

Barker, K. F., K. J. Burns, J. Klicka, S. M. Lanyon & I. J. Lovette. 2013. Going to extremes: contrasting rates of diversification in a recent radiation of New World passerine birds. Systematic Biology 62 (2): 298-320.

Lovette, I. J., J. L. Pérez-Emán, J. P. Sullivan, R. C. Banks, I. Fiorentino, S. Córdoba-Córdoba, M. Echeverry-Galvis, F. K. Barker, K. J. Burns, J. Klicka, S. M. Lanyon & E. Bermingham. 2010. A comprehensive multilocus phylogeny for the wood-warblers and a revised classification of the Parulidae (Aves). Molecular Phylogenetics and Evolution 57: 753-770.

Birds of the Sun

Handsome sunbird Aethopyga bella, photographed by Tonee Despojo. This species was only recently separated at species level from the lovely sunbird Aethopyga shelleyi; one of the distinguishing features of the two is the purple ear-patch in A. bella.

The sunbirds are definitely forerunners in the tally of the world's most brilliantly coloured birds. This family of long-billed nectar-feeders, found in tropical regions of the Old World, is often compared to the New World hummingbirds. Like hummingbirds, the males of most sunbirds shimmer with brilliant iridescent colours (the exceptions are the spiderhunters of the genus Arachnothera); the females are much more restrained, generally shades of olive-green or brown. However, though hummingbirds are committed aerialists (as befits their relationship with the swifts and nightjars), sunbirds are, as Passeriformes, more likely to feed while perched on a stem alongside their chosen flower. Also, while sunbirds are primarily nectar feeders, they also feed to a fair extent on small insects (this is also true of hummingbirds).

Male (above) and female (below) of fork-tailed sunbird Aethopyga christinae. Male photographed by Frankie Chu, female by Neil Fifer.

Sunbirds are also a rather less diverse group than hummingbirds, both in number of species and in external appearance. Because of their structural similarity, authors have differed in the number of genera recognised in the family, but one group that has generally been differentiated is the Aethopyga sunbirds of southern Asia. Aethopyga species tend to be smaller than other sunbirds, with relatively short but strongly downcurved bills. The male has the central tail-feathers elongate (Ali & Ripley 1999). Aethopyga species are also distinguished from other sunbirds by the structure of the tongue. As with other sunbirds, the tongue is elongate, with the sides curved inwards to form a double tube. Differing from others, the end of the tongue is divided into two inwardly open tubes but with a basal bifurcated plate connecting the tubes:

Tongues of sunbirds of different genera showing differences in morphology, from Cheke & Mann (2001).

Cheke & Mann (2001) listed seventeen species of Aethopyga, with an eighteenth species being added by Mann (2002). Several of these species are also currently recognised as polytypic, with multiple subspecies. Though Mann's (2002) 'new' species was simply derived from the elevation of previously-recognised subspecies, one entirely new species of Aethopyga, A. linaraborae from Mindanao in the Phillippines, was only described as recently as 1997. No large scale analysis of the interrelationships between Aethopyga species appears to have been published as yet, but centres of diversity are the Philippines and the Himalayas.

Elegant sunbird Aethopyga duyvenbodei, photographed by Marc Thibault. Having been informed by their vernacular names that Aethopyga sunbirds are, in turn, handsome, lovely and elegant, it is all the sadder to say that this last species from Sangihe, near Sulawesi, is regarded as endangered.

REFERENCES

Ali, S., & S. D. Ripley. 1999. Handbook of the Birds of India and Pakistan, together with those of Bangladesh, Nepal, Sikkim, Bhutan and Sri Lanka, 2nd ed., vol. 10. Flowerpeckers to Buntings. Oxford University Press.

Cheke, R. A., & C. F. Mann. 2001. Sunbirds: A Guide to the Sunbirds, Flowerpeckers, Spiderhunters and Sugarbirds of the World. A & C Black Publishers.

Mann, C. F. 2002. Systematic notes on Asian birds. 28. Taxonomic comments on some south and south-east Asian members of the family Nectariniidae. Zool. Verh. Leiden 340: 179-189.

Products of Kinky Inter-species Sex

Um, maybe I don't want to know what sort of Google search will hit that post title, or who's doing the searching. I can assure you, the following post is both PG and work-safe.

I came across this post today on identifying a hybrid passerine bird. The bird in question is an entirely different individual from the one discussed here, which was also revealed not too long ago. (Offhand, the site linked to via the latter, Don Roberson's Creagrus, is well worth a look for anybody interested in birds.)

Both of these birds belong to the family Parulidae, the so-called American 'warblers' - an entirely distinct and unrelated family from the various 'warblers' of the Old World (previously Sylviidae, but see here - Don Roberson again - for a good summary of the collapse of that family) and from the Australasian 'warblers' of the family Acanthizidae. Interestingly, Parulidae seems to have produced a large number of recorded hybrids over the years (enough that many have been awarded their own common names), and attention has been drawn to the fact that a greater number of recorded hybrids have been between members of different genera than members of the same genus (those that are members of the same genus have invariably been very closely-related species). The same pattern has been recorded in South American manakins (Pipridae) (Stotz, 1993). Even if we admit the point that a 'genus' is simply a grouping defined by the author and has no objective reality, it still remains arguable that hybrids are always between very closely or distantly related species, never between fairly closely related species.*

*My apologies for the revoltingly turgid sentence.

Parkes (1978) commented on this phenomenon, and suggested that barriers to hybridisation may be more heavily selected for between closely-related and sympatric species for which hybridisation may be more of a risk. This theory has also been supported by work on courtship songs in insects where sympatric species of lacewing have very different songs, while different species from Asia and North America have very similar songs, and members of one species will actually respond if they hear songs from the other 'wrong' species (Henry et al., 1999).

Perhaps the best comment on all this, though, comes from my partner - when I told him that I was posting on an interspecific hybrid, he seemed rather incredulous that a bird had mated with a member of a different species, and when considering why commented, "that must be one ugly bird".

REFERENCES

Henry, C. S., M. L. Martínez Wells & C. M. Simon. 1999. Convergent evolution of courtship songs among cryptic species of the carnea group of green lacewings (Neuroptera: Chrysopidae: Chrysoperla). Evolution 53 (4): 1165-1179.

Parkes, K. C. 1978. Still another parulid intergeneric hybrid (Mniotilta × Dendroica) and its taxonomic and evolutionary implications. The Auk 95: 682-690. Pdf here.

Stotz, D. F. 1993. A hybrid manakin (Pipra) from Roraima, Brazil, and a phylogenetic perspective on hybridization in the Pipridae. Wilson Bulletin 105 (2): 348-351. Pdf here.