For many people, watching and studying birds is exclusively a day timeactivity. However, for many birds twilight and night time are not abarrier to useful activity. It is true that very few birds areexclusively nocturnal, but many birds which are active by day alsoconduct limited, and often crucial, activities after dusk. This bookexamines many examples of the nocturnal behaviour of birds; from theoccasional night feeding of wildfowl and shorebirds to the nightsinging and night migration of certain passerines, and from thelocation of nest sites by sea birds to the nocturnal foraging of owlsand nightjars. The special cases of flightless nocturnal birds andthose birds which dwell in lightless caves are also considered.Throughout,this survey considers not only what it is that birds do at night butalso discusses how these nocturnal activities are possible. It bringstogether studies in field ornithology, sensory science, ecology andphysics and involves comparisons of the sensory capacities of otheranimals, including man. It is shown how the senses of hearing, smelland touch, as well as vision, play a crucial role in many of the nighttime activities of birds.However, these senses are not alwaysadequate for fully explaining how nocturnal behaviours are executed. Toachieve this we must look at the complex of relationships betweenbehavioural and sensory adaptations and the particular environmentswhich birds inhabit from dusk to dawn.