Food Selection by Takahe Notornis mantelli in Relation to Chemical Composition

Abstract

Selective feeding by the Takahe Notornis mantelli, an endangered, flightless, herbivorous rail, endemic to New Zealand, was studied in the Murchison Mountains, Fiordland, between 1976 and 1980. Takahe occupy the alpine grasslands throughout the snow-free period and have a simple diet consisting of leaf bases of snow tussock grasses (Chionochloa pallens, C. flavescens, C. crassiuscula) and a mountain daisy Celmisia petriei. Changes in seasonal diet between plant species and between plants of the same species were examined in relation to the mineral nutrient, carbohydrate, lipid and soluble sugar content. Tussock species eaten by Takahe contained more nitrogen, phosphorus, potassium, calcium, sodium and soluble sugars than those eaten less frequently or avoided, but selection for specific nutrients changed seasonally. Takahe selected within and between species for high concentrations of nitrogen and phosphorus in spring-early summer, and for carbohydrates in late summer-early autumn. Amongst the tussock grasses, the birds displayed a preference for actively growing, nutrient-rich tissue and appeared to differentiate between species and among sites along an altitudinal gradient to take advantage of interand intra-specific differences in the onset of growth flushes. Takahe also favoured leaf bases of flowering tussock tillers. Observations of Takahe feeding behaviour on Chionochloa pallens showed that the birds sampled widely before intensively feeding on a tussock. It is suggested that the basis for food selection involves discrimination by visual qualities and chemical cues associated with taste.