Integrating GPS Telemetry and NDVI Using the Relative Route Utilization Index for the Ural Saiga Population

Quantifying spatial use by migratory ungulates requires movement and environmental data at comparable spatial and temporal scales. We developed the Relative Route Utilization Index (RRUI) to aggregate annual route geometries when original time-stamped GPS fixes are unavailable. The study covered five districts of the West Kazakhstan Region used by the Ural saiga population (Saiga tatarica) during 2012-2024. We consolidated 184 telemetry records into 113 animal-year routes and combined district-year RRUI values with growing-season MODIS NDVI, climate variables, and livestock numbers in a balanced panel of 65 district-year observations. RRUI averaged 0.200 (SD = 0.187; range = 0.000–0.626), indicating substantial variation in the relative distribution of tracked routes among districts and years. Two-way fixed-effects models produced consistently negative RRUI coefficients across three specifications (−0.0184, -0.0163, and −0.0172). However, the RRUI–NDVI association was not statistically robust under CR2 and wild cluster bootstrap inference, which accounted for only five spatial clusters. The results therefore do not establish a robust or causal effect of saiga space use on vegetation condition. RRUI is a transparent aggregation measure for aligning annual routes with management-scale environmental data. It does not replace established movement models and should not be interpreted as a measure of population abundance, residence time, grazing damage, or movement intensity. The analysis code and computational workflow are available in an open repository.