The Greater Antillean Oriole Icterus dominicensis has recently been been split into four species (Price & Hayes, 2009; Chesser et al. 2010): Bahama Oriole I. northropi (Andros and formerly Abaco), Cuban Oriole I. melanopsis (Cuba, Isla de Pinos), Hispaniolan Oriole I. dominicensis (Hispaniola) and Puerto Rican Oriole I. portoricensis (Puerto Rico). Of these, the Bahama Oriole is of particular concern owing to its extremely small estimated population.
Recent surveys of the eastern site of Andros recorded a total of 81 orioles on North Andros, 22 on Mangrove Cay, and 24 on South Andros. Given 50 – 100% detectability, this would put total numbers at 127 – 254 (M. Price in litt. 2010). Surveys did not extend to the interior (pine forest) and western side (mangrove), however the orioles are thought to be rare or absent from these habitats. (M. Price in litt. 2010; Currie et al. 2005). Habitat on Wood Cay may be suitable, but other cays within and around Andros are thought likely to be too small to support an oriole population. It formerly also occurred on Abaco, but disappeared for unknown reasons in the early 1990s.
Perhaps the two most significant threats are brood parasitism by Shiny Cowbird Molothrus bonariensis, which arrived in the 1990s, and lethal yellowing, which has destroyed entire communities of coconut palm within the last five years, such as that of Staniard Creek (97% mortality, M. Price in litt. 2010). In 2009 orioles were completely absent from this settlement, where they were formerly common. Lethal yellowing appears to not have reached South Andros or Mangrove Cay, as they had very healthy palm populations in 2009, and there appears to be a much higher density of orioles on South Andros and Mangrove Cay than on North Andros (M. Price in litt. 2010). Additional potential threats include forest fires, logging and invasive species (in particular rats and feral cats).
On the basis of this information it seems reasonable to assume a declining population numbering fewer than 250 mature individuals. The species would then qualify as Critically Endangered if either (i) no subpopulation numbers more than 50 mature individuals, or (ii) if at least 90% of individuals are in one subpopulation. Subpopulations are defined as geographically or otherwise distinct groups in the population between which there is little demographic or genetic exchange (typically one successful migrant individual or gamete per year or less). (IUCN 2001). If the Bahama Orioles on North Andros, Mangrove Cay and South Andros can be considered to belong to a single subpopulation following the above definition it would seem appropriate to classify the species as Critically Endangered under criterion C2a(ii). If however there are two or more subpopulations, it would be Critically Endangered under C2a(i) if no subpopulation numbers more than 50 mature individuals, or Endangered under at least criteria C2a(i) and D if at least one of the subpopulations contains over 50 mature individuals.
Comments on the subpopulation structure of this newly-recognised species (as well as any other relevant information on distribution, population trends and threats) are therefore particularly welcomed.
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. Ornithol. 22:19-25, 2009
Chesser et al. (2010) Fifty-First Supplement to the American Ornithologists’ Union Check-List of North American Birds. The Auk 127: 726-744.
Currie, D. et al. (2005) Habitat Distribution of Birds Wintering in Central Andros, The Bahamas: Implications for Management. Caribbean Journal of Science, Vol. 41 (75-87).
No related posts.