Predicting mistletoe seed shadow and patterns of seed rain from movements of the mistletoebird, Dicaeum hirundinaceum

Abstract

At the scale of an individual host, mistletoes are aggregated in space, resulting from the preferential perching of mistletoe dispersers on previously infected plants. We hypothesized that the landscape scale movement patterns of mistletoe dispersers will also promote the aggregation of mistletoes. This hypothesis was tested by predicting the seed shadow for box mistletoe Amyema miquelii (Loranthaceae) and patterns of seed rain, by combining radiotelemetry data of mistletoebird Dicaeum hirundinaceum (Dicaeidae) movements with existing gut passage time data. Thirteen adult mistletoebirds had a mean home range of 20 ha, with core activity areas of approximately 1 ha, and birds more often used areas with high levels of mistletoe infestation. The predicted seed shadow of box mistletoe was leptokurtic, with a 12%, 35% and 23% probability of mistletoe seed being deposited 0 m (same host tree), 1-50 m and 51-100 m from the host tree, respectively. Although rare (3% probability), long distance dispersal of mistletoe (>500 m) can occur. The predicted patterns of seed rain were strongly aggregated, with birds dispersing large amounts of seed (>66 000 per ha) in areas with higher mistletoe infestation levels. The movements of mistletoe dispersers will therefore promote mistletoe aggregation at a landscape scale. © 2007 Ecological Society of Australia.