Scientists who are investigating the spread of invasive bird species in South Africa have asked avid bird ringers and birders to take more careful note of the presence of possible invading species, in an effort to help future related research projects.
They also made a call on people who are importing animals and birds foreign to South Africa as pets to make very sure that they are never released into the wild, where they can establish and potentially become a threat to South Africa’s local species.
This follows two recent research articles by researchers of the DST-NRF Centre for Invasion Biology at Stellenbosch University, featuring the results of studies on how two of the world’s 100 worst invasive alien species, the Indian Myna (Acridotheres tristis) and the European Starling (Sturnus vulgaris), have established and became invasive in South Africa.
In a study, led by Dr Cécile Berthouly-Salazar and published in PLOS One, the CIB research team found that the spread of Indian Mynas mirrored the importance of dispersal traits during range expansions. The fact that they have a longer wingspan or larger heads, make it easier for these individual birds to fly and disperse to new regions, where, if conditions are suitable, they can become established.
Dr Cang Hui led a study on the European Starling, which was published in Ecography. They found that starlings in their native and non-native ranges move around and into new areas based on the “good-stay, bad-disperse” rule. This means that they are quite flexible to stay in one area or move to another, depending on the level of environmental conditions being experienced.
“If conditions deteriorate, for instance, because of climate change, they will be likely to disperse and invade other areas of South Africa with more suitable conditions,” Dr Hui predicts. Currently, the European Starling is found in an L-shaped region south to the 30 degree latitude along the coast of the Western, Eastern and Northern Cape, as well as Kwazulu-Natal, but they have been spotted in Gauteng too.
For the paper in Ecography, Dr Hui and his fellow researchers delved into the ringing records from 1909 to 2008 of European Starlings that are available from the British Trust for Ornithology.
Ringing records and distribution records for this species in South Africa are lacking and generally limited to Cape Town, where 18 European Starlings were first introduced in 1897 in an effort to make the Cape look more “British”.
“If more local ringing records of these species were available, we could make much more accurate estimates about future movement trends of this species,” added Dr Hui by way of asking local ringers to also focus on invasive species when marking birds.
“Science citizenry is very important to research,” Dr Hui believes. “The information that the public help to gather can provide valuable data for researchers to work with.”
The two researchers agree that the early detection and rapid response to possible invasive species are of utmost importance. They say that it is extremely difficult to stop the spread of a specific species once it has become established, especially in such a large area of the host country.
“The population viability simply becomes too strong, and we seldom have enough resources to keep eradication programmes on indefinitely,” says Dr Berthouly-Salazar.
“Even better resourced countries like Australia have given up trying to eradicate the European starling from their shores,” adds Dr Hui.
The use of pathogens as a biological control measure against invasive bird species is not advised. “Such an approach can be highly risky and controversial as these pathogens might target local species and threaten both natural bird communities and domestic fowl industries,” says Dr Hui.
“There’s a window of opportunity in which you can try to remove invading birds from a system, but once this period of about 40 years has past, it’s almost impossible to do anything further to curb their spread,” says Dr Hui. “We are nearing a time in which we have to start considering these ‘invaders’ as an inevitable part of our environment, and handle them accordingly.”
Engela Duvenage, Media: Faculty of Science, Stellenbosch University
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