Uncapped tubular poles along high-speed railway lines act as pitfall traps for cavity nesting birds
Man-made ecosystems, such as those associated with transport infrastructure, are common worldwide, offering both opportunities and risks to wildlife. Thus, it is essential to ensure the appropriate design and monitoring of such structures to facilitate their integration into the environment. Here, we investigated the impact of uncapped tubular poles supporting the overhead wires (termed catenary) along a 19.1-km stretch of the Madrid-Levante high-speed railway line in central Spain on birds in the surrounding environment. A total of 162 bird carcasses were found in the 96 poles three and a half years after construction of the railway, showing that these poles inadvertently function as pitfall traps for birds. Repeat monitoring of a subsample of 61 poles 88 and 105 weeks later revealed a further 38 carcasses. Mortality was significantly higher at certain poles; however, no temporal or spatial pattern at the landscape scale was detected. Eight out of 10 species found dead were cavity nesters, with the Spotless Starling Sturnus unicolor being the most affected species. Two species, the Lesser Kestrel Falco naumanni and the Little Owl Athene noctua, are regionally, nationally and internationally protected, with several open-country species with declining trends also being detected. Given the extent of this type of infrastructure in Spain, we estimate that several thousand birds die as a result of uncapped tubular poles annually. This problem could be easily averted by the compulsory use of capped poles, which would prevent birds from falling inside, along railway lines and other similar infrastructure erected in natural environments that may have a similar impact.