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The breeding biology of the Intermediate Egret. Part 1: the physical and behavioural development of the chick, with special reference to sibling aggression and food intake.


The development and behaviour of marked chicks in two broods of the Intermediate Egret Egretta intermedia plumifera are described. Incubation was 26 (±1)days, the chicks flew at six and seven weeks old, and were fed at the nest until about ten weeks, when they left the heronry. The rate of food bolus delivery to the nest was greatest when chicks were 8-16 days old but the frequency of feeding visits increased after brooding finished (chicks older than 20 days). About twice as much food was delivered to the nest with twice as many chicks. Feeding success was directly related to age and to success in fights among three siblings to 12 days old. Older siblings seldom fought and had about equal feeding success overall. Aggressive and begging displays which may enhance feeding success are described.

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