Biomass burning in the Neotropics is exposing migrating birds to elevated fine particulate matter concentrations

Aim: A unique risk faced by nocturnally migrating birds is the disorienting influence of artificial light at night (ALAN). ALAN originates from anthropogenic activities that can generate other forms of environmental pollution, including the emission of fine particulate matter (PM2.5). PM2.5 concentrations can display strong seasonal variation originating from natural and anthropogenic processes. How these processes affect seasonal associations with ALAN and PM2.5 for nocturnally migrating birds has not been documented.

Location: Western Hemisphere

Time period: 2021

Major taxa studied: Nocturnally migrating passerine (NMP) bird species

Methods: We combined monthly estimates of PM2.5 and ALAN with weekly estimates of relative abundance for 164 NMP species within the Western Hemisphere derived using bird observations from eBird. We identify groups of species with shared associations with PM2.5.

Results: PM2.5 was lowest in North America, especially at higher latitudes during the boreal winter. PM2.5 was highest in the Amazon Basin, especially during the dry season (August-October). ALAN was highest within eastern North America, especially during the boreal winter. For the NMP species, PM2.5 associations reached their lowest levels during the breeding season (<10 μg/m3) and highest levels during the non-breeding season, especially for species that winter in Central and South America (~20 μg/m3). Species that migrate through Central America in the spring encountered similarly high PM2.5 concentrations. ALAN associations reached their highest levels for species that migrate (~12 nW/cm2/sr) or spend the nonbreeding season (~15 nW/cm2/sr) in eastern North America.

Main conclusions: We did not find evidence that the disorienting influence of ALAN enhances PM2.5 exposure during a stopover in the spring and autumn for NMP species. Rather, our findings suggest biomass burning in the Neotropics is exposing NMP species to consistently elevated PM2.5 concentrations for an extended period of their annual life cycles.

研究目的：夜间迁徙鸟类面临的一项独特风险，源自夜间人工光（Artificial Light at Night, ALAN）带来的导航干扰效应。夜间人工光源自人类活动，而这类活动还会产生其他形式的环境污染，其中就包括细颗粒物（Fine Particulate Matter, PM2.5）的排放。细颗粒物浓度会因自然与人为过程呈现显著的季节波动，但目前尚无研究阐明这些过程如何影响夜间迁徙鸟类与夜间人工光、细颗粒物之间的季节关联模式。
研究区域：西半球
研究时段：2021年
研究类群：夜间迁徙雀形目（Nocturnally Migrating Passerine, NMP）鸟类
研究方法：我们将西半球范围内164种夜间迁徙雀形目鸟类的月均细颗粒物与夜间人工光浓度数据，与基于eBird鸟类观测数据得到的该类群周相对丰度估算值进行整合，并筛选出与细颗粒物存在相似关联模式的鸟类类群。
研究结果：北美地区的细颗粒物浓度最低，高纬度区域在北方冬季时浓度尤甚；亚马孙盆地的细颗粒物浓度最高，尤以旱季（8—10月）为甚。北美东部地区的夜间人工光强度最高，同样在北方冬季时达到峰值。对于夜间迁徙雀形目鸟类而言，其与细颗粒物的关联强度在繁殖季达到最低（<10 μg/m³），在非繁殖季达到最高；其中在中美洲与南美洲越冬的类群，该浓度约为20 μg/m³。春季途经中美洲的迁徙鸟类也会遭遇相近浓度的细颗粒物污染。在北美东部迁徙或越冬的类群，其与夜间人工光的关联强度达到最高（迁徙期约为12 nW/cm²·sr，越冬期约为15 nW/cm²·sr）。
主要结论：本研究未发现证据表明，夜间人工光的导航干扰效应会加剧夜间迁徙雀形目鸟类在春秋迁徙停歇期的细颗粒物暴露风险。相反，研究结果显示，新热带区的生物质燃烧使得该类鸟类在年度生命周期的较长时段内，持续处于高浓度细颗粒物的暴露环境中。