Avian fruit consumption and seed dispersal in a temperate Australian woodland



Abstract The effectiveness of avian fruit consumers as seed dispersers of fleshy-fruited plants was studied in a temperate woodland community. As a consequence of the short and overlapping fruiting phenologies of fleshy-fruited plant species in temperate regions of Australia, there are very few avian species that are true specialist frugivores. The relative importance of bird species as fruit consumers was investigated, and how their foraging activities, movements and gut treatment of seeds affected dispersal of viable seeds away from the parent plant was examined. Fruit consumption and consumer seed dispersal capacity were assessed in this study through faecal analyses and by testing the viability of seeds that had passed through the gut of avian consumers. Behavioural observations enabled us to determine the consumption rates of, and quantities of fruit consumed by, various bird species and the amount of time spent feeding. Silvereyes (Zosterops lateralis) were the dominant fruit consumers in the community, although 19 bird species were either observed consuming fruit or provided faecal samples that contained fruit. Silvereyes had a high local abundance at the site and more than 90% of silvereyes’faecal samples contained the seeds of fruiting plants (n = 409). Large numbers of fruit were consumed per visit by silvereyes, particularly for Rhagodia parabolica (fragrant saltbush). Silvereyes consumed an average of four R. parabolica fruit per 5 s and up to a maximum 40 fruit per visit. Viability was high for seeds recovered from silvereyes’faeces (R. parabolica, 94.4% viable; Hymenanthera dentata, 100% viable). However, the number of seeds per faecal sample was high for R. parabolica, which may result in density-dependent seed mortality. Gut passage rate for silvereyes fed R. parabolica fruit in captivity was 31.5 ± 1.9 min. Silvereyes remained at fruiting plants for very short periods (average 50-60 s) and in most cases moved away from the parent plant, primarily toward canopy trees. Given the short visit duration of silvereyes, individuals would have left the parent plant well before seeds passed through the gut. Rhagodia parabolica fruit was consumed by a large number of bird species in the community, including species often thought of as exclusively insectivorous or nectarivorous. These species are likely to disperse viable R. parabolica seeds into microhabitats different from those visited by silvereyes.