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

Abstract

SummaryHabitat suitability models can guide species conservation by identifying correlates of occurrence and predicting where species are likely to occur. We created habitat suitability models for the White-breasted Thrasher Ramphocinclus brachyurus, a narrowly distributed endangered songbird that occupies dry forest in Saint Lucia and Martinique. Eighty-five percent of the global population inhabits two ranges in Saint Lucia, both of which are largely unprotected and threatened by development. We developed three habitat suitability models using Maxent techniques and published occupancy datasets collected from the species’ two Saint Lucian ranges, and used abiotic, land cover, and predator distribution predictors. We built one model with occupancy data from both ranges, and two others with occupancy data specific to each range. The best full-range model included 11 predictors; high suitability was associated with close proximity to Saint Lucia fer-de-lance Bothrops caribbeaus range, moderately low precipitation, and areas near streams. Our assessment of suitable sites island-wide was more restricted than results from a recent model that considered older land cover data and omitted predator distributions. All sites identified in our full-range model as highly suitable were in or adjacent to the species’ current designated range. The model trained on southern range occurrences predicted zero suitable habitat in the northern range, where the population is much smaller. In contrast, the model trained on northern range occurrences identified areas of moderate suitability within the southern range and patches of moderately suitable habitat in the western part of the island, where no White-breasted Thrashers currently occur. We interpret these results as suggesting that White-breasted Thrashers currently occupy virtually all suitable habitat on the island, that birds in the northern range occupy marginal habitat, or that an important correlate of suitability is missing from the model. Our results suggest that habitat management should focus on currently occupied areas.

Small‐scale species distribution model identifies restricted breeding habitat for an endemic island bird

“…true absences are not needed). Maxent can also model continuous and categorical variables and is relatively insensitive to small sample sizes (Phillips et al, 2006;Sass et al, 2017;Syfert, Smith & Coomes, 2013). We used Maxent version 3.4.1 (Phillips, Dud ık & Schapire, 2019) with combined nest locations from 2017 and 2018 as presence data, with duplicate nest locations (within the same 10-m cell) removed.…”

“…Even based on very limited species occurrence data, these spatial models are able to predict a species' distribution by identifying areas of suitable habitat with matching environmental and ecological parameters (Franklin, 2013). Many studies using SDMs have been carried out on bird species (Kalle et al, 2017;Latif et al, 2015;Moradi et al, 2019;Pietersen et al, 2018;Tinoco et al, 2009), including on islands (Massaro et al, 2018;Sass, Mortensen & Reed, 2017). Maxent, a machine learning method based on the theory of maximum entropy, is one of the most commonly used algorithms in SDM (Phillips et al, 2006).…”

Phylogenomics clarifies biogeographic and evolutionary history, and conservation status of West Indian tremblers and thrashers (Aves: Mimidae)

“…The subspecies differ in plumage, ecology, and potentially calls (John 1995;Cody, 2005). The subspecies sanctaeluciae , which has been considered a separate species (Cory, 1887;Ridgway, 1907), has a larger population but has saturated available suitable habitat on the island (Sass et al, 2017). Elevating sanctaeluciae to species status would likely result in IUCN Red-list categories of endangered for sanctaeluciae and critically endangered for brachyurus in Martinique.…”

Current status of the Endangered White-breasted Thrasher (<em>Ramphocinclus brachyurus</em>), a dry forest songbird endemic to Saint Lucia and Martinique

“…The areas thrashers use also have relatively high invertebrate density and are more likely to contain the shrub Myrcia citrifolia-used by the species to nest in and as food (berries) for adults and chicks-than are areas not occupied by the birds. White et al (2012) and Sass et al (2017) used habitat suitability modeling to further understand environmental correlates of White-breasted Thrasher occurrence in Saint Lucia. Despite using different environmental data sets to build suitability models, both results support the species' strong positive association with coastal, riparian dry forest and negative association with areas near high human density.…”

“…This extremely small and increasingly fragmented range is the justification for the species' IUCN status of Endangered (BirdLife International 2017). The call for White-breasted Thrasher research and conservation has been answered in part by field studies of the species' geographic range (Temple 2005), habitat requirements (Temple 2005), demography (Temple 2005, Mortensen 2009, Mortensen and Reed 2016, behavior (Temple et al 2006, Mortensen 2009, Gros-Desormeaux et al 2015, and population size (Temple 2005, Young et al 2010; modeling of habitat suitability (White et al 2012, Sass et al 2017) and extinction risk (Mortensen and Reed 2016); and the completion of the first conservation plan for the Saint Lucia subspecies (Felix et al 2014). Here we review the existing body of work on the White-breasted Thrasher, and discuss anticipated environmental changes and conservation objectives with a particular focus on the Saint Lucia subspecies.…”