Sugar preference of invasive Common Mynas (Sturnus tristis)

Abstract

Nectarivorous and frugivorous birds have been found to select their diet according to sugar type and concentration. Consequently, many studies of sugar preference have been conducted on various avian species. Common Mynas, Sturnus tristis, previously known as Acridotheres tristis, are considered amongst the 100 worst invasive species worldwide and damage fruit crops in some countries. However, their sugar preferences have never been studied. Therefore, we investigated the effect of sugar type and concentration on sugar preference and assimilation efficiency in Common Mynas (n = 7). Birds were given pairwise choice tests of sugars (fructose, sucrose and glucose) of 5 g/ml (5%) to test sugar preference. Common Mynas showed preference for glucose over fructose and sucrose. To determine at which concentrations they prefer glucose, they were offered three different concentrations of glucose (5, 10 and 25%). They showed distinct preference for the 10% concentration of glucose in comparison with 5% and 25% glucose nectars. The birds maintained body mass in the respective experimental trials thus showed sufficient energy intake. Common Mynas failed to digest and absorb sucrose, but fructose and glucose were digested and assimilated efficiently for all concentrations. Results of this study showed that Common Mynas prefer glucose, especially at ~ 10% concentration. Species distribution is determined by food resources, and these results on sugar type and preference of Common Mynas might contribute to preventing or managing their spread in South Africa.