Free-roaming livestock distribution, densities and population estimates on St. Eustatius: a 2020 update
Free-roaming livestock constitute a major threat to the terrestrial and marine ecosystems of St. Eustatius. In anticipation of a government-led culling program, we repeated population surveys of feral livestock from November 2019 to February 2020. Our goal was to compare current population estimates with those presented from 2013 by Debrot et al. (2015). Population densities of goats, sheep and chickens were estimated along 33.5 km of permanent roads and trails, representing six different habitats. Each of the 13 transects was surveyed twice. The results show that densities of goats and sheep have increased significantly compared with 2013, and chickens have increased slightly. The island population estimate (± SE) based on habitat-specific detection curves for goats is 7,602 ± 1,555; for chickens the island population estimate is 2,668 ± 417. Detections of cows were too low to be included in the analysis, however these were present in town, lower Quill and grasslands. Given that sheep were primarily restricted to grasslands, the island population estimate is less exact at 4,316 ± 2,140. Nevertheless, the densities of freeroaming goats and sheep rose significantly between 2013 and 2020, and are now at levels considered extremely unsustainable considering the island’s size. Our estimates for goat densities per hectare and combined population size in the terrestrial protected areas are D = 5.93 ± 1.35 and N = 5,171 ± 1,182, compared with D = 1.09 ± 0.27 and N = 1,323 ± 329 in 2013. This suggests that the numbers of goats have increased fourfold in the parks over the past seven years, especially the northern hills. Such excessive densities of feral goats increase soil erosion and degradation, reduce organic matter, and reduce water retention in vulnerable landscapes. Feral chickens were present in all habitats but especially prevalent in urban areas. In addition to being aggressive omnivores, chickens can transmit diseases and therefore constitute a public health risk. Our results suggest that there is an urgent need to drastically reduce numbers and implement effective management of free-roaming livestock on St. Eustatius.