Department of Life Sciences, Texas A&M University-San Antonio, San Antonio, Texas, USA.
Migratory Bird Center, Smithsonian's National Zoo and Conservation Biology Institute, Washington, DC, USA.
Glob Chang Biol. 2023 Dec;29(23):6635-6646. doi: 10.1111/gcb.16935. Epub 2023 Sep 20.
Urbanization now exposes large portions of the earth to sources of anthropogenic disturbance, driving rapid environmental change and producing novel environments. Changes in selective pressures as a result of urbanization are often associated with phenotypic divergence; however, the generality of phenotypic change remains unclear. In this study, we examined whether morphological phenotypes in two residential species (Carolina Wren [Thryothorus ludovicianus] and Northern Cardinal [Cardinalis cardinalis]) and two migratory species (Painted Bunting [Passerina ciris], and White-eyed Vireo [Vireo griseus]), differed between urban core and edge habitats in San Antonio, Texas, USA. More specifically, we examined whether urbanization, associated sensory pollution (light and noise) and brightness (open, bright areas cause by anthropogenic land use) influenced measures of avian body (mass and frame size) and lateral eye size. We found no differences in body size between urban core and edge habitats for all species except the Painted Bunting, in which core-urban individuals were smaller. Rather than a direct effect of urbanization, this was due to differences in age structure between habitats, with urban-core areas consisting of higher proportions of younger buntings which are, on average, smaller than older birds. Residential birds inhabiting urban-core areas had smaller eyes compared to their urban-edge counterparts, resulting from a negative association between eye size and light pollution and brightness across study sites; notably, we found no such association in the two migratory species. Our findings demonstrate how urbanization may indirectly influence phenotypes by altering population demographics and highlight the importance of accounting for age when assessing factors driving phenotypic change. We also provide some of the first evidence that birds may adapt to urban environments through changes in their eye morphology, demonstrating the need for future research into relationships among eye size, ambient light microenvironment use, and disassembly of avian communities as a result of urbanization.
城市化使地球的很大一部分地区面临人为干扰源，推动了快速的环境变化，并产生了新的环境。城市化导致的选择压力的变化通常与表型分化有关；然而，表型变化的普遍性尚不清楚。在这项研究中，我们研究了在美国德克萨斯州圣安东尼奥市的城市核心区和边缘区的两个住宅物种（卡罗莱纳鹪鹩[Thryothorus ludovicianus]和北方红衣主教[Cardinalis cardinalis]）和两个迁徙物种（彩绘雀[Passerina ciris]和白眼维罗鸟[Vireo griseus]）的形态表型是否存在差异。更具体地说，我们研究了城市化、与城市化相关的感官污染（光和噪音）和亮度（人为土地利用造成的开阔明亮区域）是否影响鸟类身体（质量和框架大小）和侧眼大小的测量。除了彩绘雀之外，我们没有发现所有物种的核心城市和边缘栖息地之间的体型差异，而在彩绘雀中，核心城市个体较小。这不是城市化的直接影响，而是由于栖息地之间的年龄结构差异所致，城市核心区的鸟类以年轻的雀类为主，平均体型较小。与它们的城市边缘对应物相比，居住在城市核心区的鸟类的眼睛较小，这是由于研究地点的眼睛大小与光污染和亮度之间存在负相关；值得注意的是，我们在两个迁徙物种中没有发现这种关联。我们的研究结果表明，城市化如何通过改变人口结构间接影响表型，并强调在评估驱动表型变化的因素时，考虑年龄的重要性。我们还提供了一些鸟类可能通过改变眼睛形态适应城市环境的初步证据，这表明需要进一步研究眼睛大小、周围光微环境利用以及城市化导致的鸟类群落解体之间的关系。
