Archived 2015 topics: White-breasted Thrasher (Ramphocinclus brachyurus): uplist to Critically Endangered?

This discussion was first published as part of the 2013 Red List update, but remains open for comment to enable reassessment in 2015.

BirdLife species factsheet for White-breasted Thrasher

White-breasted Thrasher Ramphocinclus brachyurus occurs as two subspecies: the nominate race is restricted to the Caravelle Peninsula on Martinique (to France) (Bulens et al. 1994, Temple 2005, P. Feldman and P. Villard in litt. 1998, H. J. Temple in litt. 2003), and race sanctaeluciae occurs on the north-east coast of St Lucia between the Marquis River Valley and Frigate Island Refuge (Keith 1997, J. D. Gilardi in litt. 1999). The southern subpopulation on St Lucia is believed to comprise 90% of the population on this island and 80% of the global population. It is currently listed as Endangered under criterion B1ab(i,ii,iii,v) because it has an extremely small range and is continuing to decline, thought to be due to the clearance of coastal dry woodland to make way for agriculture, housing and tourism developments.

Surveys in 2003 and 2004 indicated a global population of 1,300-2,600 breeding adults, 1,100-2,400 on St Lucia and c.200 on Martinique (Temple 2005). In 2006 and 2007, the St Lucia population still numbered about 1,200 individuals (Young et al. 2010). However, recent information suggests that the largest subpopulation of this species (on St Lucia) may be undergoing an even more rapid decline than previously thought. Analysing six years of monitoring data showed that the southern subpopulation on St Lucia had declined by 56% over this period, from 1,766 individuals in 2006 to 760 in 2011 (Morton 2012). The population on St Lucia is now estimated to be <900 birds, with <800 in the southern subpopulation and approximately 100 in the northern subpopulation (M. Morton in litt. 2012). Linear regression predicts a very severe loss (>89%) of this species during the 10 year period from 2006-2015, predicting a population size of <200 birds by 2015. These reductions are not fully understood; it is likely that they are due to factors other than just habitat loss (Morton, M. in litt 2012). By 2008, 84 ha (12% of the range of St Lucia’s southern sub-population) had been cleared for golf course/hotel construction (M. Morton in litt. 2012). The decline at the development site was shown to be less than outside this area, suggesting that invasive species could be exerting more pressure than habitat loss, or that habitat loss is having a delayed effect (M. Morton in litt. 2012). Construction was halted but if continued, a projected 248 ha (35% of the southern range) would be lost (M. Morton in litt. 2012).

If there is sufficient information to suggest that the global population of this species is projected to decline by ≥80% in three generations (15 years), this species would warrant uplisting to Critically Endangered under criterion A4b of the IUCN Red List.

Information is requested on the global population trends, size and distribution of this species. Any further comments on the proposed uplisting are also welcome.

References:

Bulens, P. J., Le Dru, A., Tayalay, G., Bonet, J., Tanasi, M., Barré, N. and Feldman, P. (1994) Premiers resultats sur un suivi de l’avifaune de la Presqu’île de la Caravelle.

Keith, A. R. (1997) The birds of St Lucia, West Indies: an annotated check-list. British Ornithologists Union: Tring, UK.

Morton, M. N. 2012. Population trends in the white-breasted thrasher on Saint Lucia, 2006-2011. Unpubl. report to Saint Lucia Forestry Department and Durrell Wildlife Conservation Trust. DRAFT for internal circulation.

Temple, H.J. (2005) Ecology, cooperative breeding and conservation of the White-breasted Thrasher Ramphocinclus brachyurus. Thesis. Ph.D., University of Cambridge.

Young, R. P., Baptiste, T. J. N., Dornelly, A., Temple, H., Whitehead, H., Young, H. G. and Morton, M. N. (2010) Potential impacts of tourist developments in St Lucia on the Endangered White-breasted Thrasher Ramphocinclus brachyurus. Bird Conservation International 20(4): 354-364.

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5 Responses to Archived 2015 topics: White-breasted Thrasher (Ramphocinclus brachyurus): uplist to Critically Endangered?

  1. Joe Taylor says:

    The following comments were received from Jennifer Mortensen on 12 September 2013:

    … we’re currently studying the White-breasted Thrasher on St. Lucia. One goal of our ongoing work is to understand the impact of Le Paradis resort on WBTH persistence by studying the breeding success, social organization, and survival of WBTH families. We’re doing this, in part, by comparing our data collected 5-7 years after habitat loss to those collected by Temple in 2002-04 before habitat loss and to data collected in 2006-08 immediately after habitat loss. Our focus is on the Mandelé range, and particularly the remaining forest on the Le Paradis development site. Additionally, we’re using these data to construct a population viability analysis, which we expect to submit for publication within the next few months. Briefly, the PVA is showing high population persistence under most scenarios, even with further habitat loss. However, persistence is very sensitive to changes in adult survival rates and we don’t yet have a good estimate of survival post-habitat loss.

    WBTH survival and encounter rates immediately after habitat loss suggested that birds were emigrating from Le Paradis. From before to immediately after habitat loss, adult survival estimates decreased and juvenile estimates increased, though the very high errors after habitat loss prohibit comparison of survival rates between the two periods. However, encounter rates for both age classes were lower post-disturbance, remarkably so for the juveniles, suggestive of a local thrasher efflux. This pattern was also suggested by Matt Morton and colleagues’ census data (Young et al. 2010). This makes us wonder whether the potential decline Matt is currently modeling is driven by a decrease in reproduction, an increase in adult mortality, or because birds are moving out of the currently delimited (and thus surveyed) range. As for reproduction, the rates we’re measuring have remained relatively constant since before habitat loss. Hopefully we can address the survival question shortly. We’ve been re-sighting banded thrashers over the past three breeding seasons and should have robust adult and juvenile survival estimates, including the 2006-08 data, completed this year.

  2. Andy Symes says:

    Preliminary proposals

    Based on available information, our preliminary proposal for the 2014 Red List is to pend the decision on White-breasted Thrasher Ramphocinclus brachyurus and keep this discussion open until early 2015, while leaving the current Red List category unchanged in the 2014 update.

    There is now a period for further comments until the final deadline of 31 March, after which recommended categorisations will be put forward to IUCN.

    The final Red List categories will be published on the BirdLife and IUCN websites in mid-2014, following further checking of information relevant to the assessments by both BirdLife and IUCN.

  3. Andy Symes says:

    Recommended categorisation to be put forward to IUCN

    Following further review, there has been no change to our preliminary proposal for the 2014 Red List status of this species.

    This discussion will remain open for further comments and information until early 2015, and the current Red List category will remain unchanged in 2014.

  4. Andy Symes (BirdLife) says:

    Preliminary proposals

    Based on available information, our preliminary proposal for the 2015 Red List would be to continue to treat:

    White-breasted Thrasher as Endangered under criterion B1ab(i,ii,iii,v).

    There is now a period for further comments until the final deadline of 31 August, after which the recommended categorisation will be put forward to IUCN.

    The final Red List categories will be published on the BirdLife website in late October and on the IUCN website in November, following further checking of information relevant to the assessments by both BirdLife and IUCN.

  5. Andy Symes (BirdLife) says:

    Recommended categorisation to be put forward to IUCN

    Following further review, there have been no changes to our preliminary proposal for the 2015 Red List status of this species.

    The final categorisation will be published on the BirdLife website in late October and on the IUCN website in November, following further checking of information relevant to the assessment by BirdLife and IUCN.

Comments are closed.