High-speed railway infrastructure leads to species-specific changes and biotic homogenisation in surrounding bird community

Urban areas are increasingly expanding and linear infrastructure networks, including railways, are undergoing rapid development to connect these distant areas. However, this development of linear infrastructures is known to affect the surrounding faunal communities due to changes in the landscape and operation of linear infrastructures. Both positive and negative effects of linear infrastructures on adjacent faunal communities have been reported. In this study, the authors determined the influence of High-Speed Railway (HSR) infrastructure on the bird community that surrounds it. Birds were surveyed by using both linear transect and direct counting methods, both in the area directly adjacent to the railway infrastructure and 500m away from it in a period of two years of surveys. A total of 16114 individuals belonging to 71 species were recorded. The presence of the HSR caused species-specific changes in the bird communities that surround it, causing the attraction of some species and the rejection of others. Furthermore, the authors show that the presence of the infrastructure altered the natural species turnover as the landscape changes by attracting the same bird species regardless of changes in the landscape, and filtering out others. The authors propose that further work in mitigation and development plans should focus on species-specific measures to assess the risk bird communities are exposed to.

Introduction Human activities are widely known to affect the environment surrounding them, which leads to extensive research being done and targeted policies being put in place in order to assess, prevent and mitigate these effects on the environment 1,2,3. Humans increasingly tend to concentrate in small but growing urban areas separated by extensive land masses. In order to connect these urban centers, linear infrastructure networks in general, and railway lines in particular have suffered rapid development in the last decades, and are expected to keep doing so in the future 4,5,6. Specifically, high-speed railways (HSRs) are fast becoming a viable alternative to domestic flights in many countries, reducing the environmental impact of travel 8.

The development of linear infrastructures, like HSRs, has become one of the main causes of landscape change 9,10. Structures associated with linear infrastructures are among the most notable elements of the anthropogenic landscape 10,11,12, and they extend for thousands of kilometres connecting urban centers. The construction and operation of linear infrastructures produces several impacts in the ecosystems near the infrastructure 13,14. In the case of railways, very little is known about the effects they cause 13,14. Most knowledge in this regard has been extrapolated from the much better known field of road ecology, or included as a secondary part of these studies (e.g. 10,15,16,17, see 14). However, there are key differences between railways and roads that highlight the importance of the independent research of the impacts caused by railways 18. These differences are found both in the infrastructure itself (presence of catenary and other accessory structures in railways) and in the nature of the traffic (intermittent in railways, and much higher speed in HSRs) 10,18. The evidence currently available for railways shows that the ecological effects of railways on surrounding wildlife communities are generally negative 18,19,20. Negative effects of railways include habitat clearing to make way for the infrastructure, and degradation of the remaining surrounding habitat during operation 18,20. This transformation of the habitat, and the presence and operation of railways poses an important threat to biodiversity

1. Railway lines, just like roads, contribute towards habitat fragmentation, as the linear infrastructure divides the remaining available habitat into smaller patches 10,14,26,27. This affects the distribution of fauna, by conditioning its movement patterns 27,28. Furthermore, the railway infrastructure represents a barrier, which undermines connectivity among the patches of land that the rail divides
2. Although railways may represent a larger physical barrier for non-flying animals 27, they may also represent a behavioural barrier for some flying species too
3. In the case of bird communities, direct mortality due to collisions with trains is of particular concern. For gregarious species, the risk of collision is larger, as they tend to move in big flocks, making them vulnerable to collisions with linear infrastructure elements
4. Disturbances like noise, lights and vibrations caused by passing trains also cause impacts to animals in the adjacent areas 14,20,31, which may preclude the presence of certain species, and has been found to inhibit the reproduction of certain species of birds 10,32,33.

However, positive effects of linear infrastructures, including railways, have been reported 10. Linear infrastructures can increase biodiversity through edge effects as they run along different habitats 34. The infrastructure associated with transport corridors creates new niches by providing new sources of food (small mammals, insects, grains…etc.) and perching and nesting places 10,21,35,36. Thus, birds of prey have been found to hunt in the areas close to the transport lines 35, and other birds have been found to nest on the verges of the transport lines, and even on the infrastructure associated with it 10,37,38,39. However, these attraction effects that railways may have on birds may be a double-edged sword. Even if biodiversity or number of observed individuals is increased by the presence of transport infrastructure, the species that are attracted to the infrastructure may be more prone to collisions with trains or the electrical infrastructure, in the case of railways 38,39. In the case of nesting behaviour, edge effects caused by the transport lines may increase the presence of predators, reducing the nestling survival rate and thus reproductive success 40