Human activities benefit a range of animal species, the resulting presence of which in cities can have negative societal consequences. One example are food subsidies, which buffer natural variation in food availability and allow these species to maintain larger populations. These buffers will likely gain importance under future environmental change whereby natural food sources become decreasingly available. To inform on the current importance of different habitats for a bird reliant on human-made food subsidies (Lesser Black-backed Gull Larus fuscus), and its possible population response toward changes in climate and the availability of these subsidies, we characterized population-level short-term responses to variation in drivers of local food availability, both natural (weather related) and anthropogenic (fisheries activity). We expected foraging effort to vary in relation to local wind speed and soil moisture, as well as to the alternation of fisheries activity between weekdays and weekends. Individuals were predicted to adjust their foraging habitat use in response to these environmentally driven variations in effort. To this end, we analyzed GPS tracking data of 45 breeding individuals, between 2013 and 2018, nesting in the Port of Zeebrugge, Belgium. Effort was approximated as the energy expenditure rate per trip, the daily time spent away from the colony and the trip frequency, which were analyzed by means of linear mixed effects models. Habitat use per trip was compared between marine, agricultural fields and built-up areas (cities, industry and cattle farms), in a multinomial logistic model. Marine areas and agricultural fields were most frequently exploited, but all considered stressors (wind, dry conditions and inactivity of fisheries) resulted in a higher use of built-up areas. Stronger winds increased the energetic cost of foraging at sea, and thus diminished the use of marine areas, as also did the inactivity of fisheries in weekends. Dry conditions diminished the use of fields and decreased trip frequency. Built-up areas thus constitute a buffer for the variation in food availability at sea and in agricultural fields. The expected increase in frequency and severity of extreme weather events (storms and drought) under global change, combined with the disappearance of discards, may therefore result in a long-term increase in the use of urban habitats by opportunistic large Gull species.

人类活动使一系列动物物种受益，由此产生的城市中的动物物种可能会产生负面的社会后果。一个例子是食品补贴，它缓冲了食品供应的自然变化，并使这些物种能够维持更大的种群。在未来的环境变化中，由于天然食物来源越来越少，这些缓冲区可能会变得越来越重要。告知目前不同栖息地对依赖人造食物补贴的鸟类的重要性（小黑背鸥Larus fuscus)，以及人口对气候变化的可能反应和这些补贴的可用性，我们描述了人口水平对当地食物供应驱动因素变化的短期反应，包括自然的（与天气相关的）和人为的（渔业活动）。我们预计觅食努力会因当地风速和土壤湿度以及工作日和周末渔业活动的交替而异。预计个体会根据这些环境驱动的努力变化来调整其觅食栖息地的使用。为此，我们分析了 2013 年至 2018 年间在比利时泽布吕赫港筑巢的 45 只繁殖个体的 GPS 跟踪数据。努力近似为每次旅行的能量消耗率、每天离开殖民地的时间和旅行频率，通过线性混合效应模型进行分析。在多项逻辑模型中，比较了海洋、农田和建成区（城市、工业和养牛场）每次旅行的栖息地使用情况。海洋区域和农田是最常被开发的区域，但所有被认为是压力因素（风、干燥条件和渔业不活动）都导致对建成区的更多利用。更强的风增加了海上觅食的能量成本，从而减少了海洋区域的使用，周末渔业的不活动也是如此。干燥条件减少了田地的使用并降低了跳闸频率。因此，建成区构成了海上和农田粮食供应变化的缓冲。