Roads’ danger to other wildlife, such as bear and deer, have been studied extensively, partly because direct highway mortality is easily tracked by reported incidents on highways all over the US and Canada. As well, large mammal’s movement patterns have been tracked and their avoidance of roads and roaded areas have been documented. However, nobody reports bird strikes to any wildlife authority, so roadside casualties of birds are largely unknown. However, roadside strikes of owls (especially Barn Owls) and birds of prey that were attracted to road kill have been documented and are known to be extensive at some times of the year and in some parts of the country. The Yellowstone to Yukon Conservation Initiative commissioned a report on how paved roads may affect wild birds. The report aimed to compile and distill previous research to date.
Aside from the direct effect of casualties of birds due to collisions with cars, there are many indirect effects that play a role. Studies have shown that birds avoid high-traffic areas on paved roads, which can reduce their use of roadway habitat by 30-100%. The ‘zone of disturbance’ extends up to 1km from the high-traffic area, depending on the volume of traffic on the road! One group of ornithologists found that the density of birds wasn’t different close to roads, but the males were less successful in courting a mate as their territories were nearer the highway, possibly because their songs could not be heard as well because of traffic noise. What’s more, males that were unsuccessful in previous years moved further from the road in subsequent years, but were replaced by naïve males who were then less successful in attracting a mate. This effect could potentially be worse for birds than total avoidance, because it reduces the productivity of the population as a whole. Not all birds are repelled from roadways. Shrub and scrub loving birds are drawn to roadways because of the habitat that is created due to frequent mowing and clearing of trees that happens on road shoulders. However, these birds are subject to danger from passing traffic, they may have less ability to attract mates, and their nests are at risk from mowing and brush clearing that takes place in the summer months.
Highway lighting may be an obstacle for migrating birds. It has long been observed that birds will circle around bright lights at sea for hours on cloudy nights. The same effect could be happening on roadways around the world, but has yet been unstudied. Regardless, a Dutch team found that installing green lights on rigs at sea greatly reduced the number of birds that were attracted. Road salt was long considered an attractant for resident birds, contributing to the amount of vehicle collisions with them. However, there is now some evidence that birds may die from ingesting excessive amounts of this salt as well. Considering how much area paved roads take out of habitat across the country, these effects could have a big impact on wild birds. Some measures that could be taken involve reducing or changing the lighting along highways, introducing seasonal speed limits in high-collision areas, and replacing berry-producing shrubs along roadways with plants that are less attractive to birds.
by: Your Bird Oasis