Archived 2010-2011 topics: Bahama Oriole (Icterus northropi): newly-split and Critically Endangered or Endangered?

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).

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3 Responses to Archived 2010-2011 topics: Bahama Oriole (Icterus northropi): newly-split and Critically Endangered or Endangered?

  1. I’d like to offer a few comments.

    1. Two more papers should be cited for the data used to split the species: Garrido et al. 2005 (The genus Icterus in the West Indies. Ornitologia Neotropical 16:449-470) and Sturge et al. 2009 (Colonization of South America from Caribbean islands confirmed by molecular phylogeny with increased taxon sampling. Condor 111:575-579).

    2. Melissa Price’s manuscript detailing the population size and nesting habitat should be submitted to a journal any week now. The summary by Andy Symes portrays her findings accurately. Melissa also has a molecular data set she is currently working on to assess genetic variation and structure among the three major cays. The birds are very difficult to capture, so she does not have a large data set, but it should be informative. She may be able to reach conclusions within a few months. She was told of an oriole pair at a resort on the western coast of North Andros, well removed from the bulk of the population along the eastern side of the island. The three major cays are separated by relatively small stretches of water, so the birds very likely move freely between adjacent cays. I personally suspect that all three cays support a single subpopulation as defined by IUCN.

    3. The birds prefer to nest in the tallest palm trees available, and those furthest removed from other vegetation, which explains their preference for introduced species like the Coconut Palm. The native palms are more tolerant of lethal yellowing than most introduced species, so the orioles may be able to switch again to native palms, though this could influence their fitness (boas thrive on Andros, though numbers are reduced in populated areas because people readily kill them).

    4. Coppice habitat appears to be important for the orioles year-round, and this habitat continues to decline. A major road, for example, is currently being constructed on South Andros that is destroying a large swath of this sensitive habitat and will lead to more loss with the planned farming and development that the road is intended to serve. Continuing loss of this habitat should be considered among the “additional potential threats.”

    5. The pine forest is very extensive and harbors some orioles in scattered patches of coppice and/or palm understory. All evidence suggests that the birds, however, are very scarce in the pine habitat during the breeding season, and frequent anthropogenic fires are detrimental to the native palms. Palm patches scattered among the extensive mangrove flats might also support orioles. More surveys would be helpful.

    6. The Shiny Cowbirds, fortunately, are not especially common, and do not appear to be substantially increasing. However, Melissa has confirmed prior observations by Michael Baltz that the cowbirds regularly parasitize oriole nests.

    7. Unfortunately, we do not know how population trends have changed over time on Andros.

  2. Will Mackin says:

    It sounds as if this species meets the endangered criterion but is trending towards the critically endangered level. The fact that the Abaco population want extinct recently and that Andros has similar but later developing conservation issues is a cause for alarm. Regardless of which criterion it fits, I hope the listing will call attention to the time-sensitive needs of this species.

  3. I would like to bring to the attention of those individuals studying the Bahama Oriole, that while working at the US Navy AUTEC site in central Andros over the past week I have observed birds regularly. I have been visiting the site since 2006 and can report that birds are present at the site and have been showing clear nesting behaviour. Please forgive me if this site is already known to you, I hope you find the information useful. If I can be of any further help, or if more details or photos are required please do not hesitate to contact me.
    Kind regards
    Leigh

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