5 Aug 2010

Bahama Oriole on the edge

By David Wege
The splitting of the Greater Antillean Oriole Icterus dominicensis into four separate species – as detailed in a recent paper by Melissa Price and Bill Hayes - has formally been accepted by the American Ornithologists' Union. This taxonomic revision results in the “creation” of four new island endemics – the Bahama (I. northropi), Cuban (I. melanopsis), Hispaniolan (I. dominicensis) and Puerto Rican (I. portoricensis) orioles. New species are always a source of excitement, but in this case the intrigue is overshadowed by a sense of alarm and urgency. The Bahama Oriole has entered the role call of species as one of the rarest birds in the Caribbean. It used to be found on the Bahamian islands of Abaco and Andros. However, the Abaco population was extirpated during the early 1990s (for reasons unknown) and there is strong evidence that the Andros population is in decline. Recent survey work on North Andros, Mangrove Cay and South Andros suggests a population that could be as low as 127 - 254 individuals. During a 1997 survey only one individual in juvenile plumage was seen, indicating a dramatically low reproductive output (although more juveniles have been found during more recent work). The orioles live in mature coppice woodland, and nest in endemic thatch palm and non-native coconut palms. Lethal yellowing disease of the coconut palm has wiped out this nesting tree is parts of North Andros, such as at Staniard Creek where the oriole was previously common but is now absent. Lethal yellowing appears not to have reached South Andros or Mangrove Cay, and in 2009 both had very healthy palm populations, and higher densities of orioles than North Andros. However, apart from losing nesting habitat, the oriole is also threatened by the recent arrival of the Shiny Cowbird Molothrus bonariensis – a brood parasite that targets Icterus species. So, with a declining population that could be less than 250 individuals, the Bahama Oriole would qualify as Critically Endangered on the IUCN Red List. The formal Red List categorisation of the species is currently being worked on by BirdLife, but if it is indeed Critically Endangered it would join a list of 14 other Caribbean bird species that are perilously close to extinction and in urgent need of conservation action. Photo: Bahama Oriole (Melissa Price) Footnote: It was suggested that the Bahama Oriole was a separate species by Garrido, O. H., Wiley, J. W. and Kirkconnell, A. (2005) The genus Icterus in the West Indies. Orn. Neotrop. 16: 449-470. (as detailed in a previous news story here). Further conclusive evidence was presented in the paper by Price, M. R. and Hayes, W. K. (2009) Conservation taxonomy of the Greater Antillean Oriole (Icterus dominicensis): diagnosable plumage variation among allopatric populations supports species status. J. Carib. Orn. 22:19-25. The molecular argument was also given in Sturge, R. J., Jacobsen, F., Rosensteel, B. B., Neale, R. J and Omland, K. E. (2009) Colonization of South America from Caribbean islands confirmed by molecular phylogeny with increased taxon sampling. Condor 111: 575-579. The elevation of four species from the Greater Antillean Oriole as described by Price and Hayes has just been accepted by the AOU checklist committee with the results published in: Chesser, T. R. et al. (2010) Fifty-First Supplement to the American Ornithologists' Union Check-List of North American Birds. Auk 127(3):726-744.