Birds crossing over roads: species, flight heights and infrastructure use

How high do birds fly above roads, and how do they use the road infrastructure (bridges, lampposts etc.)? These questions are rarely explored in ecological studies but were addressed by us during research in 2016–2018 in southern Poland. In total, 1665 individual birds belonging to 24 species were recorded. Species differed significantly in the height at which they crossed over roads, but about 30% of all crossings were at heights below 12 m, hence at potential collision heights. The proportion of birds perching on lampposts in the central reservation between carriageways also differed significantly between species. The surrounding landscape and road infrastructure, especially lampposts, modified the species composition associated with roads. This knowledge has practical importance, not only in regard to collisions, but also to much less studied aspects such as plant seed dispersal and/or corrosion of the infrastructure. Lampposts, as a taller component of the infrastructure, may not directly affect vehicle-bird collisions, but a flight to them may be a risky business, and we recommended higher lampposts to discourage low-level flights. This information may need to be incorporated into future studies on road ecology, as well as in mitigation programs.