Global Ecology and Conservation (Nov 2023)
Non-systematic surveys reveal increases in areas occupied by endangered and data-deficient Nubian bustard
Abstract
A large proportion of endangered species lack good-quality data for assessing population trends. Obtaining these data is especially challenging in remote arid ecosystems, in part because these desert environments have historically attracted less scientific attention and funding than more mesic areas. The Sahara-Sahel biome in northern Africa is home to over 1000 species of terrestrial vertebrates, of which 79 have been classified as threatened or near-threatened by the IUCN Red List. This includes the Nubian bustard (Neotis nuba), a species with deficient ecological information and unknown population trends. In this study we used non-systematic data collected over a 10-year period (2008–2017) across the Termit and Tin-Toumma National Nature Reserve in Niger to i) study the temporal trend in the proportion of areas occupied, ii) map occurrence, and iii) assess how vegetation productivity, elevation, and surface roughness affect species occupancy. We implemented a single-species, multi-year site-occupancy model with an intrinsic conditional autoregressive structure to account for detection probability and the spatial autocorrelation nature of the non-systematic patrolling dataset. Our results showed that birds were imperfectly detected, and detection probability increased for longer transects. Occupancy probability was higher in higher elevated areas and in smoother terrain. Contrary to expected, occupancy probability decreased with increasing vegetation productivity. However, all parameters presented high uncertainty. We found a small positive trend in the proportion of areas occupied by Nubian bustards across the study area and mapped the spatial distribution after accounting for the spatial autocorrelation. Our study provides a better understanding of the population status of Nubian bustards across the ecosystem and will serve as a guide to target and improve surveys for future conservation efforts. Systematic data collection is always advisable for monitoring biodiversity. However, our analysis demonstrates that combining advanced modeling with observations from non-systematic patrolling activities in protected areas can be used for assessing population trends of other endangered and data-deficient species across remote areas.
