Although most species within a family seem However, among closely related families, some striking differences occur, as in the passerines just mentioned, and also among waders, in which plovers (Charadriidae) migrate more by day than sandpipers (Scolopacidae). Comparing different families, there is no obvious and consistent connection between migration times and difficulty of journey, habitat, diet or other aspects of ecology. Among non-passerines: pigeons, raptors, cranes, herons and egrets migrate by day while cuckoos, shore-birds, rails, and grebes migrate mainly by night. Among passerines: crows, finches, pipits, larks, wagtails, tits, hirun-dines and others migrate primarily by day while warblers, flycatchers, thrushes, chats and others migrate primarily by night (Table 4.1). To judge from their eye structure, diurnal birds may have no better vision at night than do humans, but this would still enable them to fly safely through the open skies, and recognise star patterns and landscape features that might help them find their way.Īpart from soaring landbirds, which depend on daytime thermals, it is not immediately obvious why particular species migrate at one time rather than another. What is surprising is that many normally diurnal species also travel at night. Nocturnal species such as owls and nightjars, or optional diurnal-nocturnal species such as shore-birds, might be expected to migrate under cover of darkness. Some birds migrate mainly by day and others mainly by night.
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