Deferred independence and prolonged infantile behaviour in young varied tits, Parus varius, of an island population

In identical conditions under captivity, island fledglings of the varied tit, Parus varius, showed begging behaviour for about three times as long as did mainland fledglings. Moreover, the begging posture and call were exaggerated in island fledglings. The exaggerated begging behaviour and its long maintenance in island fledglings are considered to contribute to the extended duration of postfledging parental care which has been observed in the field. The prolongation of begging behaviour and parental care in island varied tits seems to have been evolved as a result of the low food availability which is expected from the smaller seasonal flush of food and the high population density of the birds.