Population responses of the Endangered White-breasted ThrasherRamphocinclus brachyurusto a tourist development in Saint Lucia – conservation implications from a spatial modelling approach

Abstract

SummaryTourism development is one of the main contemporary drivers of habitat loss and fragmentation within the Caribbean Islands biodiversity hotspot. In Saint Lucia, construction of a hotel and golf course within coastal dry forest is directly threatening the largest known subpopulation of the Endangered White-breasted Thrasher Ramphocinclus brachyurus. Understanding how the species is responding to ongoing landscape change and identifying priority sites for conservation are imperative for planning its long-term conservation. In this study, a four year White-breasted Thrasher monitoring dataset (2006)(2007)(2008)(2009) and landscape-scale environmental variables were used to: a) identify, characterise and map spatio-temporal patterns of White-breasted Thrasher encounter rate (an abundance proxy) within and outside the tourist development site; b) determine landscape-scale environmental variables that influence such patterns, and c) produce an island-wide predictive map of potentially suitable habitat. Observed patterns in encounter rates within and outside the development site were consistent with thrashers being displaced from cleared areas of forest and crowding into intact forest patches to the north and west of the golf course. A year after the period of the most extensive habitat clearance, White-breasted Thrasher numbers declined markedly leading to a 55% reduction in encounter rate within the development site over the four years of the study. The habitat suitability model predicted that a range of sites outside of the known geographic range of the thrasher are potentially suitable, some of which merit further surveys for potentially undetected populations. Given these findings, it is vital that patches of suitable dry forest adjacent to the tourist development are protected and contiguous natural habitat inside the tourist development is preserved.

Breeding Density and Habitat Selection of the Grey-Headed Fish-Eagle in Noakhali District, Bangladesh

“…Due to the presence of tall trees in the study area, visibility was poor (Reuleaux et al 2013, Buckland et al 2016) beyond 480 m. We used three models in the ''Distance'' package of R software: (1) half normal with cosine adjustments, (2) uniform with cosine adjustments and (3) hazard-rate with simple polynomial adjustments (Buckland et al 2001, Thomas et al 2010, Reuleaux et al 2013). We used Akaike information criterion (AIC) and visual evaluation of quantil-quantil plots to select the model that best fit our data as these are widely used and simple approaches to determine the most suitable model (Buckland et al 2001, 2016, Thomas et al 2010, White et al 2012. We used linear regression to quantify the relationship between the number of nests recorded on a transect and the number and area of waterbodies.…”

Habitat suitability models indicate the White-breasted ThrasherRamphocinclus brachyurusoccupies all suitable habitat in Saint Lucia

“…We used published Saint Lucia White-breasted Thrasher presence data in our habitat suitability models. We combined data that had been collected across several studies: data from the Iyanola range were collected in 2003 (Temple 2005) and 2006 (Young et al 2010) ( n = 45 presence points total), and data from the Mandelé range were collected in 2006–2009 (White et al 2012; n = 67 presence points). We counted a sighting in any year as a presence point.…”

“…We chose environmental predictor variables expected to influence White-breasted Thrasher distribution (Temple 2005, White et al 2012) and that also could be acquired for all of Saint Lucia. The predictors we used included temperature and precipitation metrics, measures of topography, human density as an estimate of development extent, and land cover data (see Table 1 for data sources).…”

“…Guisan et al 2006). White et al (2012) built the first habitat suitability model for the Saint Lucia White-breasted Thrasher with these goals in mind. They found that habitat suitability was associated with river presence, distance to coast, distance to main roads, building density, mean annual temperature, temperature seasonality, and total annual precipitation, though the direction of the relationships was not specified.…”

“…Their habitat suitability map predicted high suitability in only one of the species’ two Saint Lucian ranges (Mandelé, the species’ current stronghold). Furthermore, their model identified several other regions of Saint Lucia as highly suitable, including large areas on the west and south-east coasts of the island, outside the species’ current range (White et al 2012). However, the authors acknowledge that some of these predictions, particularly the identification of large tracts of potentially suitable land on the west coast, should be treated with caution due to problems with data extrapolation and older data coverage for some environmental variables used to build the model.…”