Data from: Commonness and ecology, but not bigger brains, predict urban living in birds

Background: Several life history and ecological variables have been reported to affect the likelihood of species becoming urbanized. Recently, studies have also focused on the role of brain size in explaining ability to adapt to urban environments. In contrast, however, little is known about the effect of colonization pressure from surrounding areas, which may confound conclusions about what makes a species urban. We recorded presence/absence data for birds in 93 urban sites in Oslo (Norway) and compared these with species lists generated from 137 forest and 51 farmland sites surrounding Oslo which may represent source populations for colonization. Results: We found that the frequency (proportion of sites where present) of a species within the city was strongly and positively associated with its frequency in sites surrounding the city, as were both species breeding habitat and nest site location. In contrast, there were generally no significant effects of relative brain mass or migration on urban occupancy. Furthermore, analyses of previously published data showed that urban density of birds in six other European cities was also positively and significantly associated with density in areas outside cities, whereas relative brain mass showed no such relationship. Conclusions: These results suggest that urban bird communities are primarily determined by how frequently species occurred in the surrounding landscapes and by features of ecology (i.e. breeding habitat and nest site location), whereas species’ relative brain mass had no significant effects.

研究背景：已有多项研究表明，生活史与生态变量会影响物种实现城市化的概率。近期，学界亦聚焦于脑容量在解释物种适应城市环境能力方面的作用。然而与此形成鲜明对比的是，学界对周边区域殖民压力的影响却知之甚少——这类压力可能会干扰我们对“何种物种更易成为城市化物种”这一问题的结论推导。本研究在挪威奥斯陆的93个城市样地中记录了鸟类的存在/缺失数据，并将其与奥斯陆周边137个森林样地、51个农田样地的物种名录进行对比，这些周边样地可作为潜在的殖民源种群。

研究结果：我们发现，某一物种在城市中的出现频率（即该物种被检测到的样地占比）与其在城市周边样地中的出现频率呈显著正相关；物种的繁殖栖息地与巢址位置同样呈现这一关联。与之相反，相对脑质量与迁徙模式通常对物种的城市栖息占比无显著影响。此外，针对已发表数据集的分析表明，欧洲其他六座城市的鸟类城市种群密度，同样与城市外围区域的种群密度呈显著正相关，而相对脑质量则未表现出此类关联。

研究结论：上述结果表明，城市鸟类群落主要由物种在周边景观中的出现频率，以及其生态特征（即繁殖栖息地与巢址位置）所决定，而物种的相对脑质量并未产生显著影响。