Incubation and Nest-Building Behaviour of Black-Headed Gulls

Abstract

Abstract(1) Parental behaviour, and its development from incubation behaviour during the reproductive season, is described. (2) Day to day observations of the natural situation showed that elements of the incubation pattern persist throughout the post-hatching period but progressively decline in quantity, duration and completeness. (3) Substitution of eggs for chicks also showed that the readiness to show incubation responses in a standard incubation situation declines progressively during the post-hatching period. (4) A certain amount of experience with hatched chicks renders Black-headed Gulls incapable of immediately returning to sustained incubation behaviour if the conditions of the incubation period are restored. (5) Failure of the eggs to hatch results in extension of the incubation behaviour period beyond the normal time. (6) Premature introduction of hatched chicks in the nests of incubating gulls can cause the gulls to switch to parental behaviour and so end the incubation behaviour period before the normal time. (7) The timing of the change from incubation to parental behaviour is thus mainly a matter of external control. (8) Certain of the relationships found to hold between responses having an incubation function and responses having a nest-building function in the earlier phases also hold in the post-hatching period.