Talk Large and nonspecific bird mortality in a highspeed railway traversing a Spanish agrarian landscape

Human activities alter ecosystems where they are built and they frequently shape in the mid- or long-term their structure and function. Thus, it is essential to know how new infrastructures and technologies impact species in order to properly evaluate their foreseeable effects if they become widespread. In this context, it is urgent to estimate the magnitude and characteristics of bird mortality by high-speed railways (HSR) since (i) they remain almost unknown, (ii) HSR extension is planned or under works in several countries to compete with aircraft transport, and (iii) due to circulation speeds over 250 km/hour it might be expected that almost no bird can avoid being overrun by an approaching train. A seasonal monitoring of bird mortality was conducted in two sections of HSR adjacent to a Natura 2000 site totaling 10.6 km within Toledo Province (Central Spain), and it was complemented with experiments on carcass detectability and scavenging to correct sampling biases. In parallel birds in the surroundings were sampled seasonally (24 transects 500m length) and frequency of bird crossing the infrastructure was estimated from fixed observation stations (574 stations 10’ each). Avian community showed a year round average abundance of 280.1 birds/km2, being dominated by common species from open agrarian landscapes. However, species of conservation concern like Otis tarda and Falco naumanni were also frequent. The average frequency of birds crossing the HSR was estimated to be 276.3 individuals/km hour, 55.2% of them flying within the collision risk area under the catenary. Mortality data corrected for sampling biases allowed the estimation of total bird kill to amount 91.3 death birds by HSR km and year. Both the frequency of infrastructure crossing and bird mortality correlated significantly across species with their abundance in the area (r=0.77, p<0.001 and r=0.26, p<0.05). Thus, bird kill by the high speed train is a little selective process even though some species (e.g. Alectoris rufa, Pica pica, Columba livia) suffer a disproportionate loss due to their behavior regarding the infrastructure. Moreover, not only passerines but large and very large species like Otis tarda, Bubo bubo and Buteo buteo were also killed, denoting both an environmental and safety threat. We therefore conclude that avian mortality in high-speed railways is an issue of concern due to the actual features stated in the study. Thus, it is necessary (i) to pay attention to the problem along the planning of the infrastructure as well as (ii) develop the appropriate corrective measures to minimize avian mortality with a special focus on site of special ornithological interest.

bird-strike, collision, environmental impact assessment, high-speed train, mitigation, Natura 2000