Abundance and density estimates of landbirds on Grenada

Throughout the Caribbean, resident landbirds have been subject to proportionately limited research compared to migrant species. In Grenada in particular, there is uncertainty about the status of several regional endemics, including the Grenada Flycatcher (Myiarchus nugator) and the Lesser Antillean Tanager (Stilpnia cucullata). We conducted distance sampling point counts (n = 199) in forested and agricultural habitats across Grenada in 2018 and 2019 to estimate the distribution and relative abundance of resident bird species (n = 1,235 detections). For species with more than 30 observations, we estimated species density using hierarchical distance models, including site-specific habitat covariates of land cover and elevation. We detected over 90% (n = 32) of the previously recorded landbird species during our surveys. Species turnover was low compared to a similar survey conducted in the 1980s, with a difference of four species between the two studies. These differences could be attributed to recent introductions, seasonality, sampling intensity, or other methodological differences between these studies. We had sufficient observations to estimate density for nine resident species, including the endemic Antillean Crested Hummingbird (Orthorhyncus cristatus; 1.68 ind./ha), Lesser Antillean Tanager (1.02 ind./ha), Lesser Antillean Bullfinch (Loxigilla noctis; 0.73 ind./ha), and Grenada Flycatcher (0.59 ind./ha). Our results provide an important baseline for future monitoring and conservation work, including monitoring the impacts of climate change, provision of ecosystem services, or land use change.