Artificial nectar feeders reduce sunbird abundance and plant visitation in Cape Fynbos adjacent to suburban areas

Abstract

Globally, people feed wild animals to interact with nature. Attracting nectarivorous birds to gardens using artificial nectar feeders is increasingly popular, yet little is known about its influence on birds and the plants they pollinate. We investigated effects of nectar feeders on African birds and their plant mutualists, by conducting feeding experiments in gardens and natural vegetation along the suburban edge of the Cape Peninsula, South Africa. We compared relative abundance and local distribution patterns of nectar-specialist, nectar-opportunist and non-nectarivore bird species between feeder and control treatments. We then tested whether nectar feeders in gardens affected visitation rates to two sunbird-pollinated Erica species in neighbouring vegetation compared to control sites. Nectar feeders increased the density of nectarivores (but not non-nectarivores) in gardens but decreased their density in neighbouring vegetation, even in winter when floral abundance was high. These changes in sunbird distribution patterns had no detectible influence on visitation rates to E. abietina, but decreased visitation to E. plukenetii flowers by on average 16% at least up to 300 m of gardens with feeders. Thus, although supplementary nectar feeding may have conservation value for nectarivorous birds by reducing their urban sensitivity, it can inadvertently interfere with bird-plant pollination networks by competing with native flowers for birds’ attention.

Keywords

• Avian nectarivores
• Bird pollination
• Human-wildlife interactions
• Sugar water feeders
• Supplementary feeding
• Urban ecology