Thabiso Mokotjomela conducting field experiments in dense stands of Rooikrans (Acacia cyclops) (Photo credit: Thabiso Mokotjomela)
Birds are important role-players in the spreading of seeds from the invasive tree Rooikrans (Acacia cyclops).
The birds are especially attracted to the bright red fleshy stalks that surround the seeds. Between 1991 and 2002, conservation
authorities used biological control to reduce Rooikrans stands and seed production. While the biological control was successful in
reducing seed production, the question now remains – will birds stop visiting trees with low seed numbers, or will they return and
continue to spread Rooikrans?
A recent study by Dr Thabiso Mokotjomela, together with John Hoffmann (University of Cape Town) and C·I·B
core team member Colleen Downs (University of KwaZulu Natal), used field experiments with caged birds to see if birds disperse the
seeds from remaining Rooikrans stands.
One of the bird species used in the field experiments - the Red-eyed Dove (Streptopelia semitorquata) (Photo credit: Thabiso Mokotjomela)
Thabiso found that birds indeed removed and dispersed seeds from remaining Rooikrans stands. He further found that
seeds eaten by the granivore Red-eyed Dove (Streptopelia semitorquata) and the frugivores Knysna Turaco (Tauraco corythaix)
and Red-winged Starling (Onychognathus morio) had higher germination rates, but not the granivore Laughing Dove
(Streptopelia senegalensis). Granivores are animals and birds that feed on seeds, while frugivores are fruit eaters. Thabiso
also examined how the body size of birds influence the germination of seeds. No relationship was found between the birds’ body sizes
and the time for which the seeds stayed in the gut. This means that the birds’ body sizes could not be used to predict the length of
seed retention time in the gut and thus how far seeds might be dispersed.
Thabiso explains “Even though there were less seeds available for the birds after using biological control,
the birds continued to eat and spread the remaining Rooikrans seeds. Our next step is to use mini GPS transmitters to track the
movements of bird species that eat Rooikrans seeds. This will show us where and how far the birds spread the seeds,” says
Read the paper:
Mokotjomela, T.M., Hoffmann, J.H.
and Downs, C.T. 2015. The potential for birds to disperse the seeds of Acacia cyclops, an invasive alien plant in South Africa.
For more information, contact Thabiso at email@example.com