Diurnal and nocturnal habitat use and foraging behaviour of waders

Estuaries are key overwintering site for waders but the habitats that they rely on in these areas are threatened by sea-level rise and development. Understanding how waders use intertidal and adjacent supratidal habitats of estuarine landscapes is critical for ensuring their effective conservation but knowledge gaps remain, particularly relating to the use of supratidal habitats. There are also substantial unknowns about the nocturnal behaviour of overwintering waders, and this could result in conservation and mitigation projects not fully meeting the needs of the waders that they aim to protect.This project used a combination of diurnal and nocturnal surveys, conducted using thermal imaging and infrared night-vision, to investigate the use of intertidal and supratidal habitats by waders during the night and day (Chapter 2). This highlighted that diurnal and nocturnal behaviours showed substantial differences in many species, with crucial conservation implications relating to differing habitat use between the two periods. Investigation of a broad range of abiotic and biotic factors on habitat use by waders identified differences and behavioural adaptations in response to many of these, including weather conditions, artificial light, and anthropogenic disturbance (Chapter 3). Quantitative comparisons of the foraging behaviours of three species were then compared to assess how these differed between the day and night and in response to weather variables (Chapter 4). These comparisons detected many differences between diurnal and nocturnal foraging behaviour and in response to weather variables, with waders exhibiting a high degree of adaptability, but this flexibility appeared to be limited after dark. Chapter 5 then built upon the assessment of nocturnal foraging behaviour by investigating the influence of nocturnal variables, most importantly, artificial light, on nocturnal foraging strategies. Light at night was found to reverse many of the differences between diurnal and nocturnal behaviour, facilitating a visual foraging strategy which led to significantly higher intake rates for waders who adapted accordingly.This thesis provides extensive evidence for the importance of considering both diurnal and nocturnal behaviours of overwintering waders. It should not be assumed that waders will respond to environmental and habitat changes in the same way during both the day and night, and their effective conservation may rely upon monitoring their behaviour throughout the 24- hour cycle.