Avian ecology in a changing world

Migratory birds rely on different sites throughout their annual cycle to breed, overwinter and to stop and refuel during migration. Dependence on multiple sites means that migratory bird populations are more likely to decline than non-migratory species, and their conservation is often more complicated and requires a holistic approach with international collaborations. In a rapidly changing world there are a suite of potential threats, many caused by human activities, which can threaten the conservation of migratory birds. In this thesis, I examine how changes to prey landscapes and shifts in weather and climate could impact the behaviours of Eurasian oystercatchers Haematopus ostralegus and arctic terns Sterna paradisaea. In the four data chapters I use a combination of GPS tracking technology and field observations to investigate the species foraging behaviours, determine how they respond to weather conditions, model oystercatcher survival, and project how future climate change might alter arctic tern migration. This thesis reveals that (i) oystercatchers in the Exe Estuary may be travelling outside of the protected area to forage, with younger individuals travelling further; (ii) the survival rates of juveniles, sub-adults and adult oystercatchers in Exe Estuary were high over the last four years, indicating that the long-term population decline may be caused by factors away from the Exe; (iii) incubating arctic terns forage over seven times further from the colony than previously recorded, they do not alter their behaviour in response to the winds, and they do not forage in the same areas at the same time as fishing operations; and (iv) projected changes to environmental conditions by 2100, including a reduction in Southern Ocean sea ice, reduced primary productivity at a key stopover site and changes to wind support could affect arctic terns during the migration and non-breeding periods. Collectively this work highlights how species may respond to environmental change, and the importance of examining extrinsic factors in combination with biologging and field observations to understand animal behaviour.