Assessing the impact of transport infrastructure construction on breeding birds: A long term before-during-after experiment on female bustards

Artificialization has significantly increased in the past century, posing one of the greatest threats to the viability of animal populations. Since 1980, it has been the second-highest cause of decline in farmland bird populations in Western Europe, after agricultural intensification. Impacts occur through direct destruction of natural and semi-natural habitats or their fragmentation, and also indirectly through the alteration of abiotic and biotic conditions in surrounding habitats, a phenomenon known as the zone effect. Most studies on the effect of artificialization on birds focus on existing structures without considering pre-construction conditions, which limits the ability to accurately assess and quantify their impacts and their zone effect. These studies also often only focus on singing male birds, which are easier to monitor, although females tend to make a greater contribution to population dynamics and may behave differently than males. Taking a different approach, this study estimated the impact of linear transport infrastructure before, during and after its construction on female birds in a breeding population. The case study was the Nîmes–Montpellier high-speed railway (HSR), which crosses the Costières Nîmoises Special Protection Area, home to one of the largest populations in France of little bustards ( Tetrax tetrax ), a highly endangered farmland bird species. Over a 10-year period, female little bustards were monitored before, during and after construction of the HSR within suitable breeding habitat at stratified distances from the railway. The results revealed a significant decline in female density, with a strong avoidance of areas near the HSR, extending up to 775 m after the trains began operating. While there were no major changes in breeding habitat availability in the area, female breeding capacity dropped by 57.8 % in the zone effect area, representing 26 % of the protected area. These findings highlight the need for thorough assessments of the indirect impacts of infrastructure using robust before-during-after-distance-control-impact methods. They also show the importance of considering zone effects in environmental impact assessments and conservation planning to ensure effective protection of threatened species. • The zone effect of the high-speed railway on female little bustards is up to 775 m. • The extent and intensity of the zone effect increased with train traffic. • Female abundance fell by 57.8 % in the zone effect in less than ten years. • Despite small changes in breeding habitat availability, carrying capacity declined. • The BDACI method is essential for a robust quantification of the effects infrastructure.