Reduced reflectance and altered color: The potential cost of external particulate matter accumulation on urban Rock Pigeon feathers, Denton, TX, Summer 2020

Feather quality in birds is considered an honest signal of individual health as feather appearance and function depend on an individual’s ability to maintain them. In addition to flight and insulation, feathers are essential for social interactions and sexual selection in the form of visual signals. Airborne particulate matter (PM) can accumulate on feather surfaces and alter feather appearance. We quantified PM accumulation on Rock Pigeon (Columba livia) feathers and analyzed the spectral properties of extracted particulates. Feathers were sampled from two pigeon populations, one rural and one urban, in the Dallas-Fort Worth area, with 47% and 93% developed land cover, respectively, within 2 km of the populations. We determined accumulated PM gravimetrically after rinsing feathers and then measured the visible-near-infrared diffuse reflectance and color properties of extracted particulates. The rate of PM accumulation on rural birds was higher than on urban birds. However, feather particulates collected from urban pigeons had significantly lower total reflectance, reflectance in the visible portion of the spectrum, lightness, and hue angle compared to those of rural pigeons. The hue angle of rural feather particulates displayed a negative relationship with PM accumulation while total reflectance, reflectance in the visible range, and lightness of urban feather particulates were negatively related to PM accumulation. Our findings suggest that wild birds could incur an urban pollution penalty as PM accumulation has the potential to alter feather properties. Further research is needed to better understand the influence of external PM accumulation on the physiological and behavioral health of birds.鸟类的羽毛质量被视为个体健康的诚实信号，因为羽毛的外观与功能取决于个体维持羽毛状态的能力。除承担飞行与隔热功能外，羽毛作为视觉信号还在社会互动与性选择中发挥关键作用。空气悬浮颗粒物（Airborne Particulate Matter, PM）可在羽毛表面沉积并改变其外观。我们对原鸽（Rock Pigeon, Columba livia）羽毛表面的PM沉积量进行了定量测定，并分析了提取颗粒物的光谱特性。研究样本采集自达拉斯-沃斯堡地区的两个鸽群：一处为乡村种群，另一处为城市种群，二者周边2公里范围内的开发土地覆盖率分别为47%与93%。我们先漂洗羽毛，再通过重量分析法定量测定了沉积的PM量，并测定了提取颗粒物的可见-近红外漫反射光谱与颜色特性。乡村鸽群的PM沉积速率高于城市鸽群。但与乡村鸽群的羽毛颗粒物相比，城市鸽群的羽毛颗粒物的总反射率、光谱可见光波段反射率、明度以及色相角均显著更低。乡村鸽群的羽毛颗粒物色相角与PM沉积量呈负相关关系；而城市鸽群的羽毛颗粒物总反射率、可见光波段反射率以及明度则与PM沉积量呈负相关关系。本研究结果表明，野生鸟类可能面临城市污染代价——PM沉积具备改变羽毛特性的潜在可能。未来仍需开展更多研究，以深入阐明外部PM沉积对鸟类生理与行为健康的影响。