Large ungulate populations around the world are declining, experience range loss or even go extinct. Ecological theory predicts that a species’ vulnerability is greater at the edges of its geographic range compared to its core. However, edge populations may still be successfully managed inside reserves when the drivers of declines are addressed with priority. Our aim was to evaluate the status of Caspian red deer in Iran and address the importance of law enforcement and landscape connectivity between reserves. Using systematic occurrence records and ranger-based censuses, we applied multiple methods to model the Caspian red deer’s distribution, quantify population trajectory metrics and predict landscape connectivity. Additionally, we ran generalized linear models in a Bayesian approach to assess the importance of ranger stations and connectivity on population abundance. We estimated the population at 747 (CI 95% 604–890) individuals being confined to 21 areas, reflecting a decline by 59% compared to an estimate in 1977 with declining trajectories in 98% of reserves. The number of ranger stations was the only factor correlating with its population abundance. Moreover, extirpation and range loss mostly occurred in the periphery of its Iranian distribution, and we detected five stepping stone areas in the center of the range. Our study suggests that under conditions of heavy poaching and competition with livestock, conservation urgently needs to focus on increased law enforcement and improvement of habitat quality to stop declines and prevent extinction of this large ungulate in Iran.
