Elevational Range Changes of Tropical Forest Birds on the Small Caribbean Island of Montserrat

Aim: Globally, species are changing their ranges poleward and uphill due to climate warming. This poses a particular risk to biodiversity endemic to islands, where dispersal limitations may hinder latitudinal movement across the sea and elevational range changes can result in a smaller area of potentially suitable habitat. Few studies have examined whether bird species on small tropical islands exhibit changes in elevational ranges. Here we study elevational range changes in a forest bird community that hosts two globally threatened species, of which one is endemic to the small Caribbean Island of Montserrat.

Location: Montserrat, Lesser Antilles, West Indies.

Taxon: Forest birds.

Methods: We analysed point-count data collected between 2011 and 2024 with dynamic occupancy models which explain changes in occupancy over time by colonisation and extinction while accounting for imperfect detection. We assessed the influence of elevation on both colonisation and extinction to gather robust evidence of potential elevational range changes.
Results: We found evidence for range changes in five out of 12 species, with four species changing uphill, including the endemic Montserrat Oriole (Icterus oberi), and one species showing a range contraction towards lower elevations. However, model selection uncertainty limited our ability to infer the influence of elevation on occupancy dynamics in five species. We caution that the time span of our study may not have been long enough to detect range changes in all species.

Main Conclusions: Uphill range changes observed in this study may result from synergistic interactions of anthropogenic forest degradation at lower elevations, increasing temperatures due to global warming in the Caribbean, and other consequences of global change such as the impact of hurricanes on high elevation forest structure. Our study suggests that uphill range shifts may reduce the available habitat of a globally threatened bird species endemic to a small tropical island in the Caribbean.