User:EliteSpoon/Bird migration perils

Navigation disrupted by light pollution[edit]
Night skies are obscured by artificial lights in many cities around the world. These lights are illuminated from buildings, roads and other human structures. When flying across the city, migratory birds could become attracted to artificial lights in the sky. These birds tend to follow light beams and fly continuously in circles, dying from exhaustion or predators as the result. Increased illumination due to artificial lighting could also disrupt foraging behavior of diurnal birds, making these species forage at night, instead of the day. The negative effects from artificial lights are particularly evident in bad weather and when stars are covered by clouds, because birds that migrate at night use light beams for navigation.

Collisions with buildings[edit]
Artificial light sources can attract millions of birds to lighthouses, broadcast towers and other buildings, resulting in direct mortality of birds at night. There are less artificial lights during the day, but millions of birds still die due to direct collisions with various human made structures. Birds often fatally strike the glass because they cannot differentiate between real sky and reflection of a sky in a window. Any object that increases bird density near windows can potentially lead to higher death rates. Reflective windows are particularly dangerous as birds are often attracted to them. Placing bird attractants such as bird houses, water and nutritious vegetation near windows also increases the number of birds killed. Birds may also be impacted by bright lights at nights as they have extra-retinal photoreceptors that are disoriented by the reflection of light from these buildings. Mitigating the amount of light emitted from glass surfaces at night, such as windows, can reduce the amount of fatal bird collisions with buildings and structures. To decrease the impact of artificial lighting, many cities had implemented lights out program, in which people turn off or dim the lights in tall buildings during migration season.

Lights on tall structures can disorient migrating birds leading to fatalities. An estimated 365-988 million fatal bird collisions with buildings occur annually in North America, making human-made structures a large contributor to the decline in bird species. To reduce bird strikes, it is suggested to remove all bird attractants near the windows or to partially cover the windows. For new buildings, scientists have recommended installing windows in a way that panes reflect the ground instead of the sky.