Environmental and demographic drivers of migratory strategies in birds

在世界各地，物种的分布、丰度和行为正在随着气候变化而变化，这对物种保护提出了严峻的挑战。范围、大小和分布的变化对基于遗址的保护战略可能特别具有挑战性，这些战略构成了大多数保护立法和政策框架的支柱。由于环境和气候变化而导致的分布和丰度的变化，归根结底是复杂的生态和行为过程的结果，这些过程驱动着个体健康和人口统计。因此，理解和量化这些驱动物种对环境变化做出反应的过程是生态学和保护方面的一个重大挑战。英国和欧洲大陆的沿海地区支持着许多在亚北极和北极纬度繁殖的国际重要迁徙涉禽和野禽种群。这些迁徙物种在应对气候变化时行为的快速和持续变化可能会改变它们的非繁殖分布，需要了解这些变化的原因，以便维持有效的地点和物种保护系统。特别是，迁徙和非迁徙(即居住)个体在种群中频率的变化可以从根本上改变它们的非繁殖分布，但这种迁徙行为变化的原因尚不清楚。这些变化的一个主要潜在驱动因素是繁殖时机的变化，目前在迁徙物种中得到了广泛的报道。提前繁殖的时机可能会直接影响个体健康，如果居民往往比外来人口生育得更早，进步可能会让居民受益不成比例。例如，如果随后更早的筑巢更成功，和/或如果它们在失去巢后有更多的时间更换离合器，那么更早的春季变暖可能会使居民受益。然而，这种变化对人口数量和分布的影响也将取决于决定迁徙行为的机制，特别是居留或迁徙是对当地环境条件的临时反应，每年可能有所不同，还是对随后几年重复出现的早期生活条件的确定性反应。因此，预测迁徙行为变化对迁徙种群非繁殖性分布的影响，需要了解不同迁徙策略的适合性后果，以及导致这些差异的机制过程。解决这些问题需要模型系统，在该模型系统中，可以在同一种群中确定不同的个体迁徙策略，并且可以详细研究环境条件和个体适应性之间的联系。我们建议量化决定与不同迁徙策略相关的相对适合度的机制，以及决定启动和维持个体迁徙策略的因素，在冰岛建立的欧亚捕牡蛎种群中，既存在居留策略，也存在迁徙策略。这些信息将是预测未来气候和环境变化对迁徙物种分布的影响以及对基于地点的保护战略的影响的关键。

Throughout the world, the distribution, abundance and behaviour of species is changing in response to climatic changes, presenting severe challenges for species conservation. Changes in range size and distribution can be particularly challenging for the site-based conservation strategies that form the backbone of most legislative and policy frameworks for conservation. Changes in distribution and abundance in response to environmental and climatic changes are ultimately a consequence of the complex ecological and behavioural processes that drive individual fitness and population demography. Understanding and quantifying these processes that drive species responses to environmental change is therefore a major challenge in ecology and conservation.The coastal regions of the UK and continental Europe support internationally important populations of many migratory waders and wildfowl that breed at subarctic and arctic latitudes. Rapid and ongoing changes in the behaviour of these migratory species in response to climate change can alter their non-breeding distribution, and understanding the causes of these changes is needed in order to maintain effective systems of site and species protection. In particular, changes in the frequency of migratory and non-migratory (ie resident) individuals within populations can fundamentally alter their non-breeding distribution, but the causes of such changes in migratory behaviour are unknown. One major potential driver of these changes are the shifts in timing of breeding that are being widely reported in migratory species at present. Advanced timing of breeding can directly influence individual fitness and, if residents tend to breed earlier than migrants, advances may disproportionately benefit residents. For example, earlier spring warming could benefit residents if subsequent earlier nesting is more successful and/or if they have more time for replacement clutches following nest loss. However, the consequences of such changes for population abundance and distribution will also depend upon the mechanisms determining migratory behaviour, and particularly whether being resident or migrant is a facultative response to local environmental conditions that can vary annually, or a deterministic response to early life conditions that is repeated in subsequent years. Predicting the consequences of changes in migratory behaviour for the non-breeding distribution of migratory populations therefore requires an understanding of the fitness consequences of different migratory strategies, and the mechanistic processes driving these differences.Addressing these issues requires model systems in which diverse individual migratory strategies can be identified within the same population, and in which detailed studies of the links between environmental conditions and individual fitness are possible. We propose to quantify the mechanisms determining the relative fitness associated with different migratory strategies, and the factors determining the initiation and maintenance of individual migratory strategies, in an established study population of Eurasian oystercatchers in Iceland in which both resident and migrant strategies are present. This information will be key to predicting the consequences of future climatic and environmental change for the distribution of migratory species, and the implications for site-based conservation strategies.