The impact of the physical environment on the foraging energetics of shearwaters and the consequences for breeding success

海洋环境中食物的分布和可得性随时间和空间变化很大。这给包括海鸟和海洋哺乳动物在内的海洋顶级捕食者带来了巨大的挑战，因为它们必须在不断变化的风、波和洋流的环境中寻找食物，同时部署有效的运动策略。然而，海洋特征，如潮汐混合锋，提高了生产力，这反过来又吸引了远洋和底栖鱼类。因此，在动态的物理环境和猎物组合的可预测性之间有很强的联系。然而，自然环境对猎物在空间和时间上分布的影响，以及对海洋顶级捕食者运动决策、能量消耗和后代成功的后续影响，很少被逐日研究。对于繁殖期的海鸟来说，它们的精细运动决策通常受到陆地栖息地位置的限制。这迫使它们经常在陆地栖息地和首选的近海觅食区之间的变化不定的风浪中航行，通常相隔数十到数百公里。为了做到这一点，它们必须不断调整自己的行为，对路线选择、能量消耗和雏鸟供应产生影响。我们的项目将解开物理环境对猎物可用性、运动决策、飞行成本和雏鸟供应的影响，使用一个案例研究，涉及马恩岛海鸥（海鹦）在爱尔兰海的两个种群中繁殖。在巴德西岛上繁殖的马恩岛海鸥和曼小牛在潮汐混合锋附近觅食，即爱尔兰海滨（ISF）。马恩岛海鸥是熟练的飞行者，在这种情况下，它们是一个优秀的模式物种，因为它们利用强风和海浪进行低能量翱翔，但在低风条件下必须更频繁地拍打翅膀，这在能量上更昂贵。已知来自两个研究种群的鸟类以ISF周围重叠的觅食区域为目标，但从同一景观的相反方向操作，导致不同的能量后果和觅食策略。因此，风向条件的变化和海洋锋的维持对供应和成功饲养雏鸟至关重要。我们将使用太阳能充电的GPS和加速度计标签，以及内置ECG（测量心率）的短期高分辨率加速度计标签，在两个繁殖季节监测马恩岛海鸥的运动决策和飞行成本。加速度计提供三轴加速度数据，测量行为和翼拍频率，可以转换为飞行成本的估计，以及心率记录。精细尺度的环境数据将从整个研究区域提取，包括风和波浪，而海洋学模型将用于计算夏季过程中ISF的位置和强度。在整个夏季期间，将使用系泊回声测深仪监测远洋和底栖猎物（如鲱鱼、鲱鱼、鳕鱼、白鳕）的可用性变化，同时将使用船载回声测深仪测量整个ISF的空间猎物场。我们将在觅食旅行前后对成鸟和雏鸟进行称重，以确定运动成本和觅食努力对成鸟健康和雏鸟生长的影响。利用对海洋景观、海洋变暖和分层的预测变化，我们将模拟持续气候变化对马恩岛海鸥运动成本和觅食成功的影响。预测的景观减少和分层增加可能对繁殖马恩岛海鸥的能量收支产生不同的影响，并对种群持久性产生影响。如果我们要了解未来气候变化对这些重要生态物种的影响，这个项目至关重要。

The distribution and availability of food in the marine environment is highly variable over space and time. This creates significant challenges for marine top predators, including seabirds and marine mammals, as they must deploy an efficient movement strategy in their search for food, while navigating an ever-changing landscape of winds, waves and ocean currents. However, oceanographic features, such as tidal mixing fronts enhance productivity, which in turn attracts pelagic and demersal fish. Thus, there is a strong linkage between the dynamic physical environment and the predictability of prey assemblages. Nevertheless, the influence of the physical environment on the distribution of prey in space and time, and the subsequent consequences for marine top predator movement decisions, energetic costs, and offspring success have rarely been studied on a day-by-day basis. For breeding seabirds, their fine-scale movement decisions are typically constrained by the location of terrestrial colonies. This forces them to regularly navigate the variable wind and wave landscape between the terrestrial colony and the preferred offshore foraging areas, often separated by tens to hundreds of kilometres. In doing so they must constantly adapt their behaviour with consequences for route choice, energetic costs, and chick provisioning.Our project will disentangle the effect of the physical environment on prey availability, movement decisions, flight costs, and chick provisioning using a case study involving Manx shearwaters (Puffinus puffinus) breeding on two colonies within the Irish Sea. Manx shearwaters breeding on Bardsey Island and the Calf of Man forage around a tidal mixing front, namely the Irish Sea Front (ISF). Manx shearwaters are adept fliers and an excellent model species in this context as they use strong winds and waves for low energy soaring but must beat their wings more frequently during low wind conditions, which is energetically more costly. Birds from the two study populations are known to target overlapping foraging areas around the ISF, but operate from opposite sides of the same windscape, resulting in different energetic consequences and foraging strategies. Therefore, variability in wind conditions and the maintenance of ocean fronts are critical to provisioning and successfully rearing chicks. We will monitor the movement decisions and flight costs of Manx shearwaters across two breeding seasons using solar charged GPS and accelerometer tags, and shorter-term high resolution accelerometer tags with inbuilt ECG (to measure heart rate). Accelerometers provide 3-axis acceleration data that measure behaviour and wingbeat frequency which can be converted into estimates of flight costs, along with records of heart rate. Fine scale environmental data will be extracted from across the study area, including wind and waves, while oceanographic models will be used to calculate the position and strength of the ISF over the course of the summers. Changes in the availability of pelagic and demersal prey (e.g. herring, sprat, cod, whiting) will be monitored using a moored echosounder over the course of the summer, while the spatial prey field across the ISF will be measured using ship based echosounder surveys. We will weigh adults and chicks before and after a foraging trip to determine the consequences of movement costs and foraging effort on adult fitness and chick growth.Using projected changes to the ocean windscape, ocean warming and stratification, we will model the consequences of continued climate change on Manx shearwater movement costs and foraging success. The predicted reduction in the windscape and increased stratification could have disparate effects on the energy budget of breeding Manx shearwaters with consequences for population persistence. This project is critical if we are to understand the impacts of future climate change on these ecologically important species.