THE IMPORTANCE OF GREEN SEED IN THE NITROGEN NUTRITION OF THE ZEBRA FINCH TAENIOPYGIA-GUTTATA

Australian grass-finches are widely reported to consume large quantiti es of green seed when it becomes available, and the opportunistic bree ding of wild Zebra Finches in the arid zone has been correlated with t he occurrence of rain. In this study, green and ripe seeds were harves ted from seven pasture and weed grasses grown in experimental plots an d, along with three cereal flours and whole-egg powder, were analysed for the amino-acid composition of their protein. The relative levels o f ten amino acids essential in the diets of growing birds were compare d between samples using a cluster analysis dendrogram generated from R aabe's Similarity Index. The protein of all green seeds clustered with whole egg, and away from all but one of the ripe seeds and seed produ cts. Green and ripe seed profiles were found to be significantly diffe rent by a two-sample multivariate test of significance (Hotelling's T- 2). Histidine, lysine, phenylalanine and threonine were the amino acid s most different. Of these four amino acids, lysine and threonine (alo ng with methionine) were potentially limiting in ripe seeds when compa red with whole-egg protein. In green seeds, lysine was only marginally limiting, threonine was no longer limiting, but methionine was still limiting when compared with whole-egg protein. These results indicate that the benefit of green vs ripe seed in the diet of breeding Zebra F inches is partly a higher level of the limiting essential amino acid, lysine, and partly a higher intake and throughput of soft green seed a nd consequent greater extraction of limiting essential amino acids.