NIGHT SKY AND DARK ENVIRONMENTS: BEST MANAGEMENT PRACTICES FOR ARTIFICIAL LIGHT AT NIGHT ON BLM-MANAGED LANDS TECHNICAL NOTE 457 30 3.5.1.3 Effects on Birds Laboratory and field studies show that many bird species are subject to a wide range of effects from exposure to artificial light at night, including effects on reproduction and mating behavior, predator-prey relationships, and especially migration and orientation, which has been extensively studied. It has been long known that exposure to artificial light at night can increase egg laying in chickens and delay egg laying in songbirds (Kempenaers et al. 2010). An early experiment with juncos shows that brief exposure to artificially lit environments can alter their reproductive condition (Rowan 1925). Field studies show that artificial light at night can affect territorial singing in mockingbirds (Derrickson 1988) and the timing of dawn chorus in other songbirds (Kempenaers et al. 2010). The migratory behavior of many species of birds, especially neotropical migrants, is affected by artificial light (Gehring et al. 2009), which may attract and disorient the birds. Birds that migrate during the night are especially affected, and the effect is greatest on overcast or foggy nights or when there is precipitation associated with weather fronts. The disoriented birds may be “captured” by the light and unable to see stars or other navigation cues that they would normally use. Unable or unwilling to fly away from the light, birds can die or become injured by colliding with structures or die from exhaustion after circling the light source for hours (Larkin 2000). In a severe incident, thousands of birds may be killed in one night (Gauthreaux and Belser 2006). These types of incidents occur frequently at communication towers (Gehring et al. 2009) and have occurred at oil well drilling rig sites (Ramirez et al. 2014) and at sites with gas flares (Gauthreaux and Belser 2006). Disorientation is shown to occur among migratory birds in artificially illuminated areas that are overcast and foggy as well as by bright light sources in clear conditions. Van Doren et al. (2017) studied the attraction of migratory birds to an annual tribute that involves the illumination of New York City from dawn to dusk on September 11. Under clear conditions, they documented an increase from 500 birds within 0.5 km of the light sources before they were turned on to 15,700 birds circling within 0.5 km of the vertical high-intensity light beams shortly after illumination. Research by La Sorte et al. (2017) shows that many species of migrating birds were preferentially attracted to urban environments. This was at least in part because of the relatively high levels of nighttime lighting, especially in autumn. McLaren et al. (2018) found that autumnal migrant stopover density of birds increased in proximity to the most brightly illuminated areas. Birds killed by collision with a lighted structure at night. Steady-burning red lights on communication towers are attractive to some birds.
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