THE EFFECT OF ENERGY SUPPLEMENTATION ON THE LOCAL ABUNDANCE OF THE COMMON BLOSSOM BAT, SYCONYCTERIS-AUSTRALIS, IN SOUTH-EASTERN AUSTRALIA

This study investigates the effects of providing supplementary energy to populations of blossom bats Syconycteris australis in south-eastern Australia. This bat specializes on a diet of nectar (energy) and pollen (nitrogen), allowing the effects of energy addition to be investigated in isolation from nitrogen. Bats were marked in six independent study areas, before the addition of concentrated sugar solutions to three of the six areas. The numbers of unmarked immigrant bats in supplementary-fed areas increased compared to control areas after one and two weeks of feeding. Adult immigration was greater in supplemented areas than in control areas; however, no clear effect on juvenile immigration was detected. Juveniles may have been prevented from moving into areas of abundant food by aggressive responses of adults. The number of resident bats decreased in supplemented sites relative to control sites, again possibly due to greater intruder pressure. The suggestion of territorial behaviour in this species requires further investigation to determine the extent of any spacing behaviour. These results provide the first experimental evidence that a species of bat is limited by the availability of energy, and contrast with previous observational studies of megachiroptera that have implicated nitrogen as a limiting factor.