The provision of anthropogenic food undoubtedly influences urban bird fitness. However, the nature of the impact is unclear, with both benefits and costs of urban diets documented. Moreover, the influence of short-term fluctuations in food availability, linked to urban weekday/weekend cycles of human presence, is largely unknown. We explored whether breeding red-winged starlings Onychognathus morio in Cape Town, South Africa, altered foraging and provisioning behaviour between days with high human presence (HHP) and days with low human presence (LHP)—i.e. weekdays versus weekends and vacation days. We investigated the relationship between starling diet, adult body mass and nestling development. Breeding adults consumed and provisioned the same quantity of food, but a significantly greater proportion of anthropogenic food on HHP compared to LHP days. Adults apparently benefited from the anthropogenic diet, experiencing significantly greater mass gain on HHP days. However, nestlings experienced a cost, with the number of HHP days during the nestling period associated negatively with nestling size. Adults may, therefore, benefit from the high calorie content of anthropogenic food, while nestlings may be negatively affected by nutrient limitation. The quantity of food available in urban environments may, therefore, benefit adult survival, while its quality imposes a cost to nestling growth.

人为食物的提供无疑会影响城市鸟类的健康。然而，影响的性质尚不清楚，城市饮食的收益和成本都有记录。此外，与城市工作日/周末人类存在周期相关的粮食供应短期波动的影响在很大程度上是未知的。我们探讨了是否繁殖红翅椋鸟Onychognathus morio在南非开普敦，在人多的日子（HHP）和人少的日子（LHP）之间改变了觅食和供应行为——即工作日与周末和假期。我们调查了椋鸟饮食、成年体重和雏鸟发育之间的关系。与 LHP 天相比，在 HHP 上繁殖的成年人消耗和提供相同数量的食物，但人为食物的比例要大得多。成年人显然从人为饮食中受益，在 HHP 日的体重增加明显更大。然而，雏鸟经历了成本，雏鸟期间的 HHP 天数与雏鸟大小呈负相关。因此，成年人可能会受益于人为食物的高卡路里含量，而雏鸟可能会受到营养限制的负面影响。因此，城市环境中可用食物的数量可能有利于成年人的生存，而其质量却对雏鸟的生长造成了成本。