Background The Cantabrian brown bear is a population of Eurasian brown bears (Ursus arctos arctos) living in the Cantabrian Mountains in northern Spain. Once found throughout most of the Iberian Peninsula, brown bear populations were increasingly restricted and reduced because of habitat degradation and fragmentation, poaching and poisoning, low social acceptance and low genetic variability. A Conservation Action Plan for the Eurasian brown bear was approved by the European Commission in 2000, and most of the bear distribution areas are now part of the Natura 2000 network. The demographic trend has been positive in the last decade, partly due to various conservation and dissemination projects and actions. Nevertheless, the viability of the Cantabrian brown bear population is still precarious. It is listed as critically endangered in the IUCN European Mammal Assessment and is catalogued as in danger of extinction in the Spanish Red List. Bear numbers in Spain were recently estimated at about 105-130 individuals, distributed in just two main sites. Furthermore, the distribution range of the largest sub-population is steadily narrowing, especially in the crucial reproduction area of ‘Leitariegos Corridor’. Interconnectivity of the two Spanish sub-populations is particularly important from a genetic perspective. They are connected by a 50km-wide ‘inter-population corridor’, which is in an acceptable conservation state. However, the corridor is only sporadically used by the bears because their ability to cross it is hindered by obstacles such as roads, railways and a ski resort. Objectives The corredores oso project aimed to contribute to the present and future recovery of the brown bear in the Cantabrian Mountains by improving habitats in areas considered ecological corridors for bears. The project targeted two particular bear corridors: 1. The ‘Leitariegos’ corridor - used as a breeding ground for the western population 2. The inter-population corridor – used for movement between the two sub-populations To deliver improved conditions, the project planned to focus on inter-related activities: Specific habitat enhancement and management actions Reducing threats, such as illegal snares and poisoning Improving the social climate for bears, particularly by supporting local councils and the public living in the ‘inter-population corridor’ area to undertake bear conservation and habitat management/enhancement measures. A major specific objective was to improve connectivity of the two population areas, serving both to reduce the fragmentation risks for the western population of brown bear and increase the genetic diversity of inter-connected sub-populations. Results The 'Corredores oso' project has successfully improved the social and environmental conditions for the recovery of brown bear populations in the Cantabrian Mountains of northern Spain. It has also contributed to the conservation and management of eight Natura 2000 sites. The project importantly promoted the compatibility of bear conservation with economic activities. The project was able to create a positive social and political atmosphere by reaching out directly to local stakeholders. It conducted interviews, information meetings and educational activities with local groups, including schools. It furthermore developed specific collaboration agreements with local authorities and co-operative actions with hunting societies, farmers and beekeepers. This co-operation showed improved understanding that bear conservation can be compatible with human activities. The project improved environmental conditions for the bears through the purchase of nearly 90 ha of estates and woodlands in the Leitariegos corridor and habitat enhancement through plantation of more than 15 000 cherry and chestnut trees to increase food availability. This provided new areas of suitable habitat next to the existing bear territories. It successfully applied principles of ecological connectivity to reduce risks of fragmentation within and between the two populations. Important outcomes of these activities included reductions in illegal traps and poaching, which remain the main threat to the conservation of bears. A field patrol formed of two local inhabitants was also created, which provided improved bear-presence data. Although it is not possible to see major changes in the bear populations during the lifetime of the project, sighting data did find evidence of bears using the inter-population corridor at least for feeding and resting. The identification of 21 females with cubs was also particularly encouraging. The project has hopefully paved the way for sustainable land management in co-operation with key local stakeholders that should help bear populations in the long-term. It has set solid ground for the integration of bear conservation principles into the policy making of local councils in the inter-population corridor. A management plan was also produced, which can act as a "pilot plan" for the management of rural mountainous areas in Spain. A Handbook of Good Practice in corridor management can additionally support similar efforts for large mammals elsewhere. Further information on the project can be found in the project's layman report and After-LIFE Conservation Plan (see "Read more" section).