Avian assemblages in invasive acacia thickets

Invasive species often have negative impacts on native species and ecosystem services, with some areas so entirely transformed that recovery of the natural vegetation is nearly impossible. Such impacts lead many to assume that invaded areas have little ecological value. However, few studies have examined which and how many species use habitats dominated by invasives. Knowing this is crucial for making baseline comparisons to other habitat types, especially when the invaded habitat occurs in a highly transformed landscape.

With this in mind, C·I·B student, Andrew Rogers, and his supervisor, Steven Chown, examined bird assemblages within highly transformed habitats created by invasive Australian acacia in the Western Cape, South Africa. After enduring nearly six months of fieldwork and a case of tick bite fever, Andrew found that the most abundant birds in acacia thickets were habitat generalists and fed mostly on seeds or a mixture of seeds and insects. Surprisingly, acacia thickets were found to support more than 70 native bird species, a large range of functional body sizes and moderate bird densities relative to indigenous vegetation. What this means is that while acacia thickets cannot support entire native species assemblages, they do provide a structurally complex, low-disturbance habitat which birds utilize. Importantly, the results, published in Diversity and Distributions, showed that these transformed landscapes should not be easily dismissed despite their non-native status, and that from a birdís point of view, acacia thickets may provide important habitat. Their study set the stage for others to investigate how invaded areas influence landscape connectivity and sustain native populations of birds and other native species.

Cape Weaver begins a nest in a flowering Port Jackson acacia

Cape Weaver begins a nest in a flowering Port Jackson acacia (Acacia saligna)

Cape Weaver begins a nest in a flowering Port Jackson acacia

Acacia thickets, such as this one near Cape Town, create novel habitats in the Western Cape. Despite the largely negative impact of acacia invasion on fynbos habitats, these thickets provide habitat for more than 70 native bird species.


Read the paper:

Rogers, A. M. & Chown, S. L (2013) Novel ecosystems support substantial avian assemblages: The case of invasive alien Acacia thickets. Diversity and Distributions. doi/10.1111/ddi.12123/pdf

For more information contact Andrew Rogers at