Insides 2/6/04 9:38 am Page 108 Whittaker et al. 108 Bull. B.O.C. 2004 124(2) References: Brumfield, R. T., Swofford, D. L. & Braun M. J. 1997. Evolutionary relationships among the potoos (Nyctibiidae) based on isozymes. Pp. 129-145 in Remsen, J. V. (ed.) Studies in Neotropical ornithol- ogy honoring Ted Parker. Orn. Monogr. No. 48. Cleere, N. 1998. Nightjars. A guide to the nightjars and related nightbirds. Pica Press, Robertsbridge. Dickerman, R. W. & Phelps, W. H. 1982. An annotated list of the birds of Cerro Urutaní, on the border of Estado Bolívar, Venezuela and Território Roraima, Brazil. Amer. Mus. Novit. 273: 1–20. Hilty, S. L. & Brown W. L. 1986. A guide to the birds of Colombia. Princeton Univ. Press. del Hoyo, J., Elliott, A. & Sargatal, J. (eds.) 1999. Handbook of the birds of the world, vol. 5. Lynx Edicions, Barcelona. Olivares, A. 1964. Adiciónes a las aves de la Comisaría del Vaupés (Colombia), II. Caldasia 9: 379–393. Roca, R. L. 1994. Oilbirds of Venezuela: ecology and conservation. Publ. Nuttall Orn. Cl. 24. Cambridge, MA. Ridgely, R. S. & Greenfield, P. J. 2001. The birds of Ecuador. Cornell Univ. Press, Ithaca, NY. Sick, H. 1993. Birds in Brazil: a natural history. Princeton Univ. Press. Snow, D. W. 1962. Natural history of the Oilbird Steatornis caripensis, in Trinidad, W.I. Part II. Population, breeding, ecology and food. Zoologica 47: 199–221. Addresses: Andrew Whittaker, Conjunto Acariqara, Rua Samaumas 214, Manaus 69085-410, Amazonas, Brazil, e-mail: [email protected]. Axel H. Antoine-Feill S. & Robin Scheiele Z., Apartado Aéreo (POB) 94438, Bogotá D.C., Colombia. © British Ornithologists’ Club 2004 Rapid speciation by a Lesser Antillean endemic, Barbados Bullfinch Loxigilla barbadensis by P.A. Buckley & Francine G. Buckley Received 9 June 2003 The small endemic West Indian emberizine known as the Lesser Antillean Bullfinch Loxigilla noctis is widespread in the Leeward and Windward Lesser Antilles (Fig. 1). It has usually been regarded as highly polytypic and nine subspecies are currently recognised (Table 1). With one exception, all are strongly sexually dichro- matic: males are jet black with rufous throats, rufous or black undertail-coverts, and black bills; females are brownish-olive, paler ventrally, with horn-coloured bills. The exception is the population found only on the isolated and geologically discrete island of Barbados. Originally described by Cory (1886) as a separate species, Barbados Bullfinch Loxigilla barbadensis, nearly all subsequent workers, hewing to 20th-century taxonomic practice, have treated it as another subspecies of the Lesser Antillean Bullfinch, its scientific name then becoming Loxigilla noctis barbadensis. However, the bullfinches resident on Barbados differ in one striking way from the other eight named populations of the Lesser Antillean Bullfinch: they exhibit no sexual dichromatism. In the light of recent treatments of other allopatric West Indian bird populations, reconsideration of the taxonomic status of barbaden- sis is warranted. Insides 2/6/04 9:38 am Page 109 P. A. Buckley & Francine G. Buckley 109 Bull. B.O.C. 2004 124(2) Background Until the mid 1980s, essentially the only examinations of Lesser Antillean Bullfinch’s biology concerned its taxonomy (Hellmayr 1938, Bond 1956). Then, Bird (1983) compared the behaviour and ecology of barbadensis with that of several other Lesser Antillean Bullfinches, especially St Lucia’s sclateri and St Vincent’s crissalis, the two geographically closest to barbadensis. Regrettably, no portion of that thesis has ever been published and, despite intense efforts, we have been unable to contact its author. It nonetheless remains a seminal work bearing on the taxonomic status of barbadensis. Equally important information concerns the geological history and age of Barbados. Here, too, the picture has now been clarified, and Barbados’s striking geological history and youth, especially its relationship to islands in the main Lesser Antillean arc, are now well understood. The third piece of the puzzle finally fell into place with publication of a recent analysis of the molecular genetics of Barbados’s breeding landbirds, including barbadensis. Geology, vegetative cover and climate Barbados is unique among the Lesser Antilles in being both very young and lacking any history of volcanism. It is also 150 km east of the main Windward Island chain, well out in the trade winds. Owing to its geological origins, it is relatively low in relief, its highest point, Mt Hillaby, reaching only 335 m, with about two-thirds of the island ranging from sea level to c.100 m, and almost another third to c.200 m. Whereas basal rocks in north-eastern Barbados have been dated to the Upper Eocene/Tertiary (50–70 My BP), these are crustal rocks pushed up as a tectonic mound along the Barbados Ridge. This feature originated (and is still rising) as the South American Plate slid west-northwestward under the Caribbean Plate, in the process heating crust that emerged as lava from volcanoes on the Lesser Antillean Ridge from Grenada to Saba, along the main Lesser Antillean arc. These present- day islands first appeared in the Miocene, 15–30 My BP, and are still rising (Speed 1988, Perfit & Williams 1989, Speed & Keller 1993). Their volcanic soils were doubtless vegetated quickly, so they would have had a long history of avian coloni- sation and evolution. ‘Proto-Barbados’ on the other hand only emerged in fits and starts at the end of the Pleistocene, c.700,000–1 My BP, and for much of its early history was a combination of coral reefs and low-lying small islands, periodically eroded, submerged and rebuilt in response to sea-level changes, oceanic and rainwater erosion, and sedimentation. On average, it has been rising c.0.3 m per 1,000 years. The best evidence (Mesolella 1967) suggests that the core of present-day Barbados emerged 600–700,000 y BP. Originally a circular dome (the centre of the uplift), perhaps two-thirds of this original island subsequently eroded away; then c.300,000 y BP, a new island arose to its south-west (near present-day Bridgetown), eventually fusing via crustal uplift with the now much smaller main island. Insides 2/6/04 9:38 am Page 110 P. A. Buckley & Francine G. Buckley 110 Bull. B.O.C. 2004 124(2) Forest vegetation was probably slow to accumulate in such a low-relief, dynamic environment, and though there are as yet no known dates for establishment, forests most probably followed on the merging of Proto-Barbados and Christ Church islands, i.e. up to 300,000 y BP. Limestone soil generated by erosion (and, eventu- ally, plant growth) was augmented by episodic infusions of volcanic ash from neighbouring St Lucia and St Vincent (e.g. an estimated 3.25 million tonnes [76 tonnes/ha] fell on Barbados following the irruption of St Vincent’s Soufrière Volcano in 1901: Gooding 1974). Many plants probably colonised Barbados from the south (but not the north or west) via ocean currents such as the Antilles Current, fed by waters draining the Amazon and Orinoco Rivers and even western Africa. Winds doubtless also brought plant propagules from South America (Urania moths still regularly arrive on Barbados with southerly winds, as do vagrant and colonis- ing birds), from West Africa, the source of airborne sediments as well as Desert Locusts Schistocerca gregaria (Prospero 1968, Rainey 1989, Savoie et al. 1989), and also from the Lesser Antilles north of Barbados. Birds might still be contribut- ing plant material and seeds from North America, the West Indies and South America in soil on their feet and in their excreta. One analysis (Gooding 1974) estimated that of 478 extant, non-introduced, higher plant species on Barbados, 12% came from the north, 19% came from northern South America, 43% occurred throughout the Caribbean/tropical continental America, and 26% were pantropical; only five (1%) were Barbados endemics. By the time of European colonisation in the early 1600s, Barbados was covered in forest, but unlike the volcanic Antillean-arc forests, it was not tropical rain forest, nor was it widespread. The high centre of the island, with good soil and 2,030 mm per year of rainfall, did support a rich mesic tropical hardwood woodland, whilst lower and drier elevations averaging 1,520 mm per year and sea coasts with only 1,015 mm per year grew only poorer hardwood and dry scrub forests, respectively. Especially on the windward side of Barbados, woody vegetation was conspicuously stunted and wind-shaped by salt spray. Although persistent east–north-easterly trade winds blow at 15–30 kph most of the year, Barbados’s low relief has eliminated most orographic precipitation, so the island is relatively dry: its mean annual rainfall of 520 mm is only about half that of St Lucia, whose tall mountains (nine in excess of 610 m, the highest 950 m) and strikingly vertical, montane topography (10% of St Lucia lies above 365 m) extract much more moisture from trade winds. Accordingly, St Lucia’s tall, lush, and highly diverse tropical rain forests and elfin woodlands are wholly lacking on Barbados. This is reflected in endemic avian species: Barbados currently has but one (a few others were probably extirpated shortly after European colonisation: Hutt et al. in press), whilst St Lucia has three (perhaps four), including two endemic genera (Keith 1997). Geographic variation within Lesser Antillean Bullfinches Nine subspecies of Loxigilla noctis have been described (Table 1), many on only minor differences in colour, patterning or (not shown)