Artificial light at night confounds broad‐scale habitat use by migrating birds

Abstract

With many of the world's migratory bird populations in alarming decline, broad-scale assessments of responses to migratory hazards may prove crucial to successful conservation efforts. Most birds migrate at night through increasingly light-polluted skies. Bright light sources can attract airborne migrants and lead to collisions with structures, but might also influence selection of migratory stopover habitat and thereby acquisition of food resources. We demonstrate, using multi-year weather radar measurements of nocturnal migrants across the northeastern U.S., that autumnal migrant stopover density increased at regional scales with proximity to the brightest areas, but decreased within a few kilometers of brightly-lit sources. This finding implies broad-scale attraction to artificial light while airborne, impeding selection for extensive forest habitat. Given that high-quality stopover habitat is critical to successful migration, and hindrances during migration can decrease fitness, artificial lights present a potentially heightened conservation concern for migratory bird populations.

Environmental effects on flying migrants revealed by radar

“…Wad Madani in Sudan, p. 275 in Drake and Reynolds 2012). Similarly, birds stop over at a disproportionately high rate in large city parks (Buler and Dawson 2014) and nearby highly light-polluted areas (Van Doren et al 2017, McLaren et al 2018).…”

Holding steady: Little change in intensity or timing of bird migration over the Gulf of Mexico

“…The importance of estimating the passage of migrants cannot be overemphasized, with a large body of literature highlighting recent declines in migratory bird populations (Askins, Lynch, & Greenberg, ; Both et al, ; Gauthreaux, ; Møller, Rubolini, & Lehikoinen, ; Nebel, Mills, McCracken, & Taylor, ; Robbins, Sauer, Greenberg, & Droege, ). Natural and anthropogenic obstacles abound for migrating birds, including predation (Cimprich & Moore, ; Loss, Will, & Marra, ), habitat degradation and destruction (Norris & Marra, ; Norris, Marra, Kyser, Sherry, & Ratcliffe, ), collisions with structures (e.g., buildings, communication towers, wind turbines) (Loss, Will, Loss, & Marra, ; Loss, Will, & Marra, ), and attraction to artificial light at night (Cabrera‐Cruz, Smolinsky, & Buler, ; Van Doren et al, ; McLaren et al, ; La Sorte, Fink, Buler, Farnsworth, & Cabrera‐Cruz, ). In addition to these factors, another fundamental challenge for migratory birds is shifts in resource availability induced by global climate change (IPCC, ), which has the potential to affect all aspects of their annual life cycle, including migration (Møller, Fiedler, & Berthold, ).…”

How to disarm an evolutionary trap

“…Second, the introduction of exotic species is a leading cause of evolutionary traps (Robertson et al, ) and are often caused by, and observable through, failure to avoid novel predators, pathogens or disease vectors (Brown & Rohani, ; Carthey & Blumstein, ; Dixson, Munday, & Jones, ). Third, “navigational traps” will be visible through atypical movement patterns between habitats and portions of the range, typically through abnormally strong avoidance or attraction to human‐altered habitats (e.g., Keefer, Peery, & High, ; McLaren et al, ), structures (e.g., Malik et al, , Szaz et al Száz et al, ), or sources of activity (e.g., Tuxbury & Salmon, ), possibly even via failure to detect dangerous man‐made objects (e.g., Grief et al Greif, Zsebők, Schmieder, & Siemers, , Figure ). Environmental change may also trigger organisms to pursue maladaptive developmental pathways (Van Dyck, Bonte, Puls, Gotthard, & Maes, ).…”

“…Migratory songbirds are attracted to heavily lighted urban areas where they are more likely to be killed by collisions with buildings (McLaren et al, 2018).…”