Habitats are changing rapidly around the globe and urbanization is one of the primary drivers. Urbanization changes food availability, environmental stressors, and the prevalence of disease for many species. These changes can lead to divergence in phenotypic traits, including behavioral, physiological, and morphological features between urban and rural populations. Recent research highlights that urbanization is also changing the gut microbial communities found in a diverse group of host species. These changes have not been uniform, leaving uncertainty as to how urban habitats are shaping gut microbial communities. To better understand these effects, we investigated the gut bacterial communities of White-Crowned Sparrow (Zonotrichia leucophrys) populations along an urbanization gradient in the San Francisco Bay area. We examined how gut bacterial communities vary with the local environment and host morphological characteristics. We found direct effects of environmental factors, including urban noise levels and territory land cover, as well as indirect effects through body size and condition, on alpha and beta diversity of gut microbial communities. We also found that urban and rural birds’ microbiomes differed in which variables predicted their diversity, with urban communities driven by host morphology, and rural communities driven by environmental factors. Elucidating these effects provides a better understanding of how urbanization affects wild avian physiology.

人居环境在全球范围内变化迅速，城市化是主要动力之一。城市化改变了粮食供应，环境压力以及许多物种的疾病流行率。这些变化可能导致表型性状的差异，包括城乡人口之间的行为，生理和形态特征。最近的研究表明，城市化也正在改变在多种寄主物种中发现的肠道微生物群落。这些变化还不是统一的，因此对于城市栖息地如何塑造肠道微生物群落尚无定论。为了更好地了解这些影响，我们调查了白冠麻雀（Zonotrichia leucophrys）的肠道细菌群落）沿旧金山湾地区城市化梯度发展的人口。我们检查了肠道细菌群落如何随当地环境和宿主形态特征而变化。我们发现环境因素对肠道微生物群落的α和β多样性具有直接影响，包括城市噪声水平和领土覆盖范围，以及通过体型和状况造成的间接影响。我们还发现，城市和乡村鸟类的微生物群落各不相同，其中变量预测了它们的多样性，城市社区由宿主形态驱动，而农村社区则由环境因素驱动。阐明这些影响可以更好地理解城市化如何影响野生鸟类生理。