Can Human Structures Help Birds?
According to the Central Intelligence Agency’s World Factbook, the total distance of roads and railways around the world is 64,285,009 kilometers. As this number continues to grow, it’s important to study how an increase in the volume of human-made transportation could impact wild animal populations, such as birds. While the negative effects of transportation infrastructure on birds have been well-reported in the field of urban ecology, positive effects have received less attention. This study reports the potential positive effects of roads and railways on bird populations.
The concentration of studies demonstrating the negative effects of transportation on birds is not entirely without cause: the documented negative effects of roads on animals is five times larger than the reported positive effects. The greatest threats of transportation infrastructure to birds can be divided into the following categories:
- Habitat loss and fragmentation from roadways.
- Environmental disturbance in the form of chemical, light, and noise pollution.
- Traffic mortality from collisions.
- Barriers to movement across roads, which may lead to fragmentation and isolation in some species.
However, certain positive effects of transportation infrastructure may mitigate some of the threats listed above. To identify these effects, researchers examined 92 peer-reviewed reports published between 1978 and 2014 on the positive impacts of roadways on birds. As long as collisions are avoided, they concluded that roads may have no effect on some species; in many cases, the effects may even be positive.
These positive impacts depend on infrastructure design and traffic congestion. Low-traffic roads or railways with roadside vegetation provide habitat for nesting and foraging. Artificial lighting increases food availability and prolongs activity during winter. For raptors, roadkill is a valuable food source. For other types of birds, roads may inhibit the movement of predators, thereby reducing predation. Moreover, structures usually found near roads, such as billboards, fences, and pylons, offer safe places for birds to perch, sing, and nest. Finally, the warmth of roads can help birds conserve metabolic energy. Overall, the types of birds that will benefit most from roads have high reproductive rates and small territories.
The study authors point out, however, that these positive impacts may be costly for predatory species who depend on some birds as a food source. Furthermore, transportation infrastructure may benefit some birds more than others, promoting homogeneity as opposed to diversity in urban bird species. Nevertheless, a better understanding of the positive effects of urbanization on wildlife (even if they are outweighed by the negative effects) may help urban planners design infrastructure that causes the least amount of damage possible.