Ecological Research

, Volume 32, Issue 5, pp 667–676 | Cite as

Invasive alien trees reduce bird species richness and abundance of mutualistic frugivores and nectarivores; a bird’s eye view on a conflict of interest species in riparian habitats

  • Joy Rumbidzai Mangachena
  • Sjirk Geerts
Original Article


Invasive alien plants have major ecological effects, in particular in riparian habitats. While effects of alien tree invasions on riparian plants are well studied, effects on animals are less well understood. Invasive alien trees can have a positive effect by adding habitat and food sources, or have a negative effect, by replacing native food plants. Here we use birds as indicators to determine the impacts of an invasive Eucalyptus tree species in riparian areas of the Cape Floristic Region (CFR) of South Africa. Birds are an ideal study group because they are mobile, respond quickly to habitat changes and feed at different trophic levels. Fixed-point bird counts were done during winter and spring at near-pristine and Eucalyptus camaldulensis invaded riparian habitats. A total of 1142 birds from 44 species were recorded. Bird assemblages in invaded sites are almost a complete subset (24 species) of those in near-pristine areas (42 species). Invaded areas were missing 18 species and contained a total of 128 fewer individuals. This is due to declines in insectivores, frugivores, granivores, raptors and omnivores and the absence of nectarivores in invaded sites. From a bird’s perspective, the prioritisation of E. camaldulensis removal from the CFR’s river systems is justified, but whether bird species will return to cleared areas needs to be determined.


Bird feeding guilds Cape Floristic Region Eucalyptus camaldulensis Nectar feeding birds Plant invasions Raptor 



We thank the landowners who allowed access to their properties and Michelle Slabber for fieldwork assistance. We thank Joseph Kioko and Mirijam Gaertner for comments on an earlier draft. We acknowledge funding from the DST-NRF Centre of Excellence for Invasion Biology and the Working for Water Programme through their collaborative research project on “Integrated Management of invasive alien species in South Africa”. Funding to SG was also provided by the National Research Foundation (Grant 87843).

Supplementary material

11284_2017_1481_MOESM1_ESM.pdf (278 kb)
Supplementary material 1 (PDF 277 kb)


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Copyright information

© The Ecological Society of Japan 2017

Authors and Affiliations

  1. 1.Department of Conservation and Marine SciencesCape Peninsula University of TechnologyCape TownSouth Africa
  2. 2.Centre for Invasion Biology, Department of Botany and ZoologyStellenbosch UniversityStellenboschSouth Africa

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