1. Altmann, S.A.: Sociobiology of rhesus monkeys. II. Stochastics of social communication. J. Theor. Biol., 8: 490–522, 1965.
2. Armstrong, E.A.: Bird Display and Behaviour. Lindsay Drummond Ltd., London, 1947.
3. Bergin, T.: Breeding biology of the budgerigar (Melopsittacus undulatus Shaw). University of New England, Armidale, N.S.W., Australia, Honours Thesis, 1968.
4. Brockway, B.F.: Ethological studies of the budgerigar (Melopsittacus undulatus): non-reproductive behaviour. Behaviour 22: 193–222, 1964
5. Ethological studies of the budgerigar (Melop-sittacus undulatus): reproductive behaviour. Behaviour 23:294–324, 1964