Monitoring of nest boxes installed as part of the LIFE PowerLines4Birds project

As part of the LIFE PowerLines4Birds project, among other initiatives, actions were planned to increase the range and breeding success of the European roller (Coracias garrulus), specifically through the installation of nest boxes on power line towers equipped with anti-electrocution devices. The installation of the 50 nest boxes was completed by the beginning of June 2025. During May and June 2026, the 50 nest boxes were monitored. This initiative took place in the Special Protection Areas (SPAs) of Castro Verde, Vale do Guadiana, Cuba, Évora, Campo Maior, and Vila Fernando—areas that are particularly important for the conservation of this species. 

Of the 50 nest boxes installed, 45 were monitored. The remaining 5 could not be assessed due to operational constraints. Each box was visited twice, two weeks apart. These visits made it possible to confirm the occupancy of the boxes, monitor the development of the nests, and estimate the age of the chicks, essential information for understanding the species’ behavior and nesting season and for planning the most appropriate time to band the birds.

Monitoring revealed that more than half of the nest boxes were occupied. Of the 45 boxes monitored, 26 were occupied and 19 were unoccupied, corresponding to an occupancy rate of 57.8%. Among the unoccupied boxes, two showed signs of bird mortality, both involving species that could not be identified. Of the 26 occupied boxes, four were being used by roller birds, all located in the Castro Verde Special Protection Area (SPA). Although this number is lower than expected, the result is positive, as it confirms that the species uses these structures and underscores the importance of installing nest boxes to support the conservation of the european roller, especially in areas where the availability of natural cavities may be limited. 

The remaining boxes were occupied by other species, namely the black starling (Sturnus unicolor; n = 9), the Lesser Kestrel (Falco naumanni; n = 7), the Little Owl (Athene noctua; n = 2), the Galician shrew (Eliomys quercinus; n = 1), and unidentified species (n = 3).

After monitoring the nest boxes and estimating the age of the chicks, they were banded with the assistance of biologist Nuno Fialho. This practice will make it possible to identify the juveniles individually, record any cases of mortality, contribute to the study of their migratory routes, and assess how these individuals might use the region’s nest boxes next year. 

Monitoring provided essential information on the effectiveness of this conservation measure, particularly regarding nest box occupancy, their use by other species, the condition of the structures, and future maintenance needs. This data will be crucial for adjusting the management of the nest boxes and contributing to the success of future breeding seasons for the European roller, one of the most endangered birds in Portugal. 

LIFE PowerLines4Birds project is co-financed by the European Union’s LIFE Program and aims to reduce the impact of power lines—through electrocution and collisions—on the Iberian Peninsula for seven priority bird species that are highly vulnerable to these threats. The partners in this project are the League for the Protection of Nature (LPN), the Portuguese Society for the Study of Birds (SPEA), QUERCUS—National Association for Nature Conservation, the Spanish Ornithological Society (SEO/Birdlife), and E-REDES.