Dispersal, germination and survival of New Zealand mistletoes (Loranthaceae): Dependence on birds

The dispersal, germination and establishment of the New Zealand Loranthaceae (Alepis flavida, Peraxilla colensoi, P. tetrapetala, Ileostylus micranthus and Tupeia antarctica) were investigated. The most important bird dispersers were tui, bellbirds and silvereyes. These birds appear to provide reasonably good quality dispersal: fruits were swallowed whole and the seeds later defecated in germinable condition; birds tended to visit plants for only 1-2 minutes and eat a few mistletoe fruits each time. Germinability of seeds ranged between species from moderate to high (17-96%). None of the study species of mistletoe germinated successfully unless the fruit skin (exocarp) was removed, by hand or by passage through a bird gut. While hand removal of the exocarp gave the same or higher percentage germination as bird removal, in the field bird dispersal is the only effective method of exocarp removal and is therefore essential. Dispersal was limiting at one of three sites studied (Craigieburn), suggesting that reductions in bellbird densities by introduced carnivores or competition for honeydew food sources may be indirectly affecting mistletoe reproduction. Establishment and survival of seedlings on host branches was low (15-28% depending on species to production of first independent leaves, 0-14% after two years). Survival of adults over one year of the study was 80% for Tupeia and 91-95% in the other species, showing that frequent establishment of seedlings is necessary for population maintenance. While disperser limitation does not seem to currently be a major threat to mistletoe survival, it must be considered as a possible factor both historically and in the future.