Red deer in the northeast of Portugal: monitoring trends in a transboundary population

Abstract

Monitoring animal population trends is essential to develop appropriate wildlife management strategies. In Portugal, red deer populations have been increasing in size and distribution over the last three decades. One of the largest free-ranging populations is located near the Portuguese-Spanish border, in the Northeast of the country. Red deer reappearance in that region dates from early 1980s, when several animals dispersed naturally from Sierra de la Culebra Regional Hunting Reserve (Zamora, Spain) into the Portuguese territory. This recolonization process has led to an increasing concern in relation to conservation, management and game exploitation of this species. An evaluation of the real population status is a key aspect for correct management planning and decision-making. By using two direct count methods, line transects and vantage points, we estimated red deer densities and other population indices (i.e. sex-ratio and recruitment rates) in the northern unit of Lombada National Hunting Area (Bragança, Portugal). Indirect methods were used to update information about distribution area. Our results showed a slow increase in the population density and a considerable geographic expansion in relation to the last two decades. Using distance sampling in line transects we estimated an average population density of 3.26 ind/100 ha (95%CI = 2.27-4.70). Furthermore, we calculated a mean population sex-ratio of 0.81 (95%CI = 0.71 – 0.92), which is close to an 1:1 proportion, and the annual variation in the number of calves per female indicated a low productive population. When comparing our results with those of Sierra de la Culebra technical plans, we found similar population indices, reinforcing the transboundary character of red deer population. We highlight the importance of regular and long-term monitoring programms and we recommend a cooperation between Portugal and Spain in red deer management. Managing transboundary populations is an interesting new challenge in wildlife management.