Unravelling networks: Causes and consequences of decreasing connectivity in bird migration pathway

Habitat loss and disturbance pose great threats to wildlife, and these may be particularly severe for migratory birds. A well-connected network of foraging, resting, breeding, and moulting sites is essential for bird migration. However, losing a key site can breakdown a bird migration network completely, and consequently trigger population declines. In this thesis, Yanjie Xu analysed long-term observations on large-scale movements by migratory waterfowl to monitor the changes in the connectivity of these bird migration networks in the past decades. The results illustrated how global changes can influence the network dynamics of migratory birds, potentially leading to population declines (Chapter 3), and rapid spread of diseases by avian hosts (Chapter 6). Moreover, she pointed out a variety of other potential consequences of connectivity loss in bird migration networks, e.g., changing patterns of gene flows, predation risks, seed dispersal, and social information diffusion (Chapter 7). Integrating the five different chapters of this thesis, Yanjie Xu proposed a practical methodological framework (Chapter 7) for setting priorities in conservation of migration networks at a variety of scales: a local scale (Chapter 4), a flyway scale (Chapter 5), and at species level (Chapter 2). Her findings give novel insights into the impact of global change on wildlife, and can facilitate systematic conservation policy making for migratory animals.