ABSTRACT: The availability of anthropogenic food subsidies has promoted an increase in generalist opportunistic gull species, which currently breed and forage on predictable anthropogenic resources (e.g. landfills). Here we investigated whether marine resources are still important to urban-dwelling gulls. We studied 4 natural and 2 urban yellow-legged gull Larus michahellis colonies and compared (1) diet composition (through pellet analysis) and (2) isotopic niches of adults and chicks, (3) diet delivered to chicks of different ages, and (4) fatty acid (FA) composition of fledglings, in order to assess diet composition, diversity and quality, and the relevance of marine prey for natural and urban gull populations. Adult urban gulls consumed considerably lower proportions of marine prey when compared to gulls from natural colonies; however, they fed their younger chicks (<20 d old) mostly with fish, representing 61-80% of their chick food deliveries. Refuse items were mostly delivered to chicks older than 20 d. Overall, urban isotopic niches were not completely distinct from those of natural colonies, in some cases sharing ca. 50% of their niche space. Fledglings from the most urbanized colony presented overall higher FA concentrations and diversity, but they were lacking some omega-3 FAs relevant to their physiology. Our results highlight the importance of marine resources in the diet of urban gulls, particularly during early chick rearing, the relevance of food sources in the area around the breeding colonies and the fact that urban gulls benefit from year-round reliable anthropogenic food resources.

中文翻译：

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海洋资源在城市海鸥饮食中的重要性

摘要：人为食物补贴的可获得性促进了多用途机会鸥物种的增加，这些物种目前在可预测的人为资源（例如垃圾填埋场）上繁殖和觅食。在这里，我们调查了海洋资源是否仍然对城市海鸥重要。我们研究了4只自然鸥和2只城市黄腿鸥Larus michahellis并比较（1）饮食组成（通过沉淀分析）和（2）成年和雏鸡的同位素3，（3）交付给不同年龄雏鸡的饮食以及（4）雏鸟的脂肪酸（FA）组成评估饮食组成，多样性和质量，以及海洋猎物与自然和城市海鸥种群的相关性。与自然殖民地的海鸥相比，成年的城市海鸥所消耗的海洋猎物比例要低得多。然而，他们以幼鱼（<20天大）为食，大部分以鱼为食，占其雏鸡食物交付量的61-80％。垃圾物品大多交付给20天以上的雏鸡。总体而言，城市同位素生态位与自然殖民地的生态位并不完全不同，在某些情况下约有共同点。他们的利基空间的50％。来自城市化程度最高的殖民地的雏鸟总体上具有较高的FA浓度和多样性，但缺乏与它们的生理相关的omega-3 FA。我们的结果强调了海洋资源在城市海鸥饮食中的重要性，特别是在早期雏鸡饲养期间，繁殖群体周围地区食物来源的相关性以及城市海鸥受益于全年可靠的人为食物资源这一事实。