Megafires and thick smoke portend big problems for migratory birds

Assessing the combined threats of artificial light at night and air pollution for the world’s nocturnally migrating birds

“…However, the occurrence of wildfires in the Northern Hemisphere during the summer (Westerling et al., 2006), a major source of PM 2.5 (McClure & Jaffe, 2018; Urbanski et al., 2008), could increase PM 2.5 concentrations during the breeding season. In addition, wildfires in western North America during the autumn (Goss et al., 2020; Weber & Yadav, 2020) could increase exposure during autumn migration (Overton et al., 2021). Unlike the breeding and non‐breeding seasons, our estimates within regions of passage contain additional complexities related to variation in the vertical distribution of air quality.…”

“…The poorest air quality during migration is likely to be encountered during stopover at ground level, especially for individuals that occur in urban areas. However, wildfires have the potential to decrease air quality substantially during migration (Ahmadov et al., 2017), forcing birds to alter migration direction/altitude, stop migrating or conduct stopovers in non‐traditional habitats (Overton et al., 2021).…”

“…These refinements enhance the toxicity of air pollution when birds undertake energetically demanding activities, such as migratory flight (Brown et al., 1997). Evidence that some species stop migrating, alter migration direction/altitude (Overton et al., 2021) or fly faster (Li et al., 2016) when encountering highly polluted air suggests that the balance these species have achieved between time, energy and risk could be disrupted (Alerstam & Linderström, 1990). The increased energy expenditure required to fly faster or higher could drain energy reserves, and refuelling in suboptimal habitats could reduce overall efficiency.…”

“…Based on evidence that ALAN attracts nocturnal migrants into dense urban areas (e.g., Van Doren et al., 2017), it is unlikely that poor air quality counteracts the attractive influence of ALAN. However, evidence that nocturnally migrating geese ( Anser albifrons elgasi ) stop migrating or alter migration direction/altitude when they encounter high PM 2.5 concentrations (>161 µg/m 3 ) suggests that extreme conditions can deter migration in some situations (Overton et al., 2021). Additional work is needed to determine how migratory birds respond when exposed to different levels, forms and sources of PM 2.5 (exposure–response relationships) and how these relationships change when ALAN is present or absent.…”

Fall bird migration in western North America during a period of heightened wildfire activity

“…The second most severe wildfire season on record for the western United States happened to be 2020, with over 58,950 wildfires burning over 10.1 million acres (CRS 2021). With the height of the fire season occurring during fall bird migration, it is possible that migratory birds were indirectly affected by wildfires across the West (Overton et al 2021). Intense wildfires have been known to instigate early or evasive migration and affect other dynamics of songbird movement (Berthold 1996, Frost 2018, Johnson 2020.…”