Rapidly increasing urbanisation requires mitigation against associated losses of biodiversity and species abundance. In urban-breeding birds, altered food availability for nestlings is thought to reduce reproductive success compared to forest populations. To compensate for shortages of preferred foods, urban parents could increase their search effort for optimal diets or provision other foods. Here, we used telemetry and faecal metabarcoding on blue tits from one urban and one forest populations to compare parental effort and comprehensively describe nestling diet. Urban parents travelled on average 30% further than those in the forest, likely to offset limited availability of high-quality nestling food (i.e. caterpillars) in cities. Metabarcoding, based on a mean number of 30 identified taxa per faeces, revealed that the diets of urban chicks were nonetheless substantially shifted to include alternative foods. While in the forest caterpillars comprised 82 ± 11% of taxa provisioned to nestlings, in the city they constituted just 44 ± 10%. Pre-fledging chick mass as well as offspring numbers were lower in urban than in forest-reared broods. Thus, at least in our comparison of two sites, the hard labour of urban parents did not fully pay off, suggesting that improved habitat management is required to support urban-breeding birds.

迅速发展的城市化要求减轻生物多样性和物种丰富度的相关损失。在城市饲养的鸟类中，与森林种群相比，改变雏鸟的食物供应量被认为会降低繁殖成功率。为了弥补首选食品的短缺，城市父母可以加大寻找最佳饮食或提供其他食品的努力。在这里，我们使用遥测技术和粪便条形码对来自一个城市和一个森林种群的蓝雀进行比较，以比较父母的努力并全面描述雏鸟的饮食。城市父母比森林父母平均旅行了30％，这可能抵消了城市中优质雏鸟食物（即毛毛虫）有限的供应。根据每个粪便中识别出的30个分类单元的平均数量进行元条形码编码，研究表明，城市雏鸡的饮食已发生了很大变化，以包括其他食物。在森林中，毛毛虫占提供给雏鸟的分类单元的82±11％，而在城市中，它们仅占44±10％。城市中雏鸡的雏鸡数量和后代数量都比森林饲养的雏鸡要低。因此，至少在我们对两个地点的比较中，城市父母的辛劳并未完全得到回报，这表明需要改善栖息地管理来支持城市繁殖鸟类。