Salleh Hudin Noraine, De Neve Liesbeth, Strubbe Diederik, Fairhurst Graham D, Vangestel Carl, Peach Will J, Lens Luc
Terrestrial Ecology Unit Department of Biology Ghent University Ghent Belgium.
Department of Biological Sciences Faculty of Science & Mathematics Universiti Pendidikan Sultan Idris Tanjong Malim Perak Malaysia.
Ecol Evol. 2017 Jun 30;7(16):6163-6171. doi: 10.1002/ece3.3114. eCollection 2017 Aug.
Several studies on birds have proposed that a lack of invertebrate prey in urbanized areas could be the main cause for generally lower levels of breeding success compared to rural habitats. Previous work on house sparrows found that supplemental feeding in urbanized areas increased breeding success but did not contribute to population growth. Here, we hypothesize that supplementary feeding allows house sparrows to achieve higher breeding success but at the cost of lower nestling quality. As abundant food supplies may permit both high- and low-quality nestlings to survive, we also predict that within-brood variation in proxies of nestling quality would be larger for supplemental food broods than for unfed broods. As proxies of nestling quality, we considered feather corticosterone (CORT ), body condition (scaled mass index, SMI), and tarsus-based fluctuating asymmetry (FA). Our hypothesis was only partially supported as we did not find an overall effect of food supplementation on FA or SMI. Rather, food supplementation affected nestling phenotype only early in the breeding season in terms of elevated CORT levels and a tendency for more variable within-brood CORT and FA. Early food supplemented nests therefore seemed to include at least some nestlings that faced increased stressors during development, possibly due to harsher environmental (e.g., related to food and temperature) conditions early in the breeding season that would increase sibling competition, especially in larger broods. The fact that CORT was positively, rather than inversely, related to nestling SMI further suggests that factors influencing CORT and SMI are likely operating over different periods or, alternatively, that nestlings in good nutritional condition also invest in high-quality feathers.
几项针对鸟类的研究表明，与农村栖息地相比，城市化地区无脊椎动物猎物的缺乏可能是繁殖成功率普遍较低的主要原因。先前对家麻雀的研究发现，在城市化地区进行补充喂养可提高繁殖成功率，但对种群增长并无贡献。在此，我们假设补充喂养能使家麻雀获得更高的繁殖成功率，但代价是雏鸟质量降低。由于丰富的食物供应可能使高质量和低质量的雏鸟都能存活，我们还预测，与未喂食的窝相比，补充食物的窝中雏鸟质量指标的窝内变异会更大。作为雏鸟质量的指标，我们考虑了羽毛皮质酮（CORT）、身体状况（标度质量指数，SMI）和基于跗骨的波动不对称性（FA）。我们的假设仅得到部分支持，因为我们未发现食物补充对FA或SMI有总体影响。相反，食物补充仅在繁殖季节早期影响雏鸟表型，表现为CORT水平升高以及窝内CORT和FA的变异性更大。因此，早期接受食物补充的窝似乎至少包括一些在发育过程中面临更多压力源的雏鸟，这可能是由于繁殖季节早期更恶劣的环境（如与食物和温度相关）条件会增加同胞竞争，尤其是在较大的窝中。CORT与雏鸟SMI呈正相关而非负相关这一事实进一步表明，影响CORT和SMI的因素可能在不同时期起作用，或者说，营养状况良好的雏鸟也会在高质量羽毛上投入。
