The relative importance of birds and insects as pollinators of the New Zealand flora

Native birds may have been underestimated as pollinators of the New Zealand flora due to their early decline in abundance and diversity on the mainland. This paper reconsiders the relative importance of birds and insects as pollinators to eight native flowering plants, representing a range of pollination syndromes, on two offshore island refuges. Experimental manipulations were made on five of these plant species to assess the relative effectiveness of bird and insect visitors as pollinators. In addition, foraging behaviour and the respective morphologies of flowers and visitors were measured at all eight plants to identify the main pollinators. The experimental measures showed that percentage fruit set was significantly higher in flowers exposed to birds than flowers from which birds were excluded in all manipulated plants. The observational measures revealed that for six of the flowering species (Sophora microphylla, Vitex lucens, Pittosporum crassifolium, Pittosporum umbellatum, Pseudopanax arboreus and Dysoxylum spectabile) the endemic honeyeaters were most likely to meet the conditions necessary for successful pollination. For the remaining two species (Metrosideros excelsa and Geniostoma ligus trifolium) the contribution by honeyeaters and insects to pollination was equivalent. The results suggest that the role of the endemic honeyeaters in pollination of the New Zealand flora, and the subsequent regeneration of native forest ecosystems, should be important considerations in ecosystem management.