Research opportunities on alien birds
Although alien species are widely (and rightly) regarded as a “bad thing”, they offer special opportunities for research! In a nutshell, many of these opportunities can be summarized into two questions: “How has the species adapted to its new environment? What impact is it having on its environment?”
Currently, 10 bird species are recognised as aliens which have established self-sustaining breeding populations in South Africa. The “natural” ranges of all these species are in the northern hemisphere, so one research opportunity is the question: “How does the timing of the major events of the annual cycle between the introduced population compare with that of the source population? Are they simply shifted by six months, or is it more complex than that?”
This article provides a list of these 10 species, and describes briefly how they arrived in South Africa. It summarizes opportunities for research. Each species is illustrated with a photograph selected from the BirdPix section of the Virtual Museum at http://vmus.adu.org.za. A few have their distributions illustrated by maps produced from the data of the bird atlas project at http://sabap2.adu.org.za .
Mallard Anas platyrhynchos
Mallards were not deliberately introduced, but were escapees from private collections of waterfowl. Sightings at wetlands started to be reported in bird club newsletters from around 1980, especially in Gauteng and the Western Cape. It was quickly discovered that they hybridize with the local ducks, and especially the Yellow-billed Duck Anas undulata. This poses a severe threat to the genetic integrity of the populations of indigenous ducks. Initial opposition to culling was largely overcome by good communication campaigns, for example this information brochure produced for Cape Town. Mallards and Mallard-hybrids are nowadays fairly consistently removed by the conservation authorities whenever they are reported. Of the 10 alien species, the Mallard is one of two which are actively and decisively controlled, and which are therefore not appropriate for observational research projects. The other species is the House Crow Corvus splendens, discussed below.
Chukar Partridge Alectoris chukar
Six Chukar Partridges were confiscated in 1964 by the customs authorities at the port of Cape Town, and were released on Robben Island, Table Bay. In 2018, the population numbered in the hundreds. The size of the population has fluctuated widely; for example during the “cat-years” of the mid 2000s, the population seemed to have been down to tens of birds. They do not appear to have crossed the 7 km of ocean to reach the mainland. There is potential as a study species.
Common Peacock Pavo cristatus
Like the Mallard, the Common Peacock is an ornamental bird, with domestic populations on many estates and around farm houses. Out in the countryside, it is often hard to classify an individual peacock as “domestic” or “feral”; in reality many are along a continuum between these two extremes, and should be classified as “semi-feral”. The distribution map below shows how widespread peacocks, feral and semi-feral, have become. However, the peacocks on Robben Island are indisputably feral. It is thought to have been introduced there in 1968 and the population has maintained itself. Increasingly, we are grasping that there are more or more feral populations scattered across the whole of South Africa. Here are links to papers in the ejournal Biodiversity Observations which describe feral populations in Bloemfontein, Free State, and Amanzimtoti, KwaZulu-Natal. There are wine farms in the Western Cape, where flocks of peacocks do substantial damage in vineyards. These are potential study sites for this species.
Rose-ringed Parakeet Psittacula krameri
The Rose-ringed Parakeet is a popular cage-bird, and escapes from captivity occur regularly. Small breeding populations seem to have been established in the main cities of South Africa multiple times, and then gone extinct. But there are now substantial populations, numbering hundreds, both in the Durban region, and in the suburbs of the cities of Gauteng. This was the study species of a recent BSc(Hons) project (Ivanova IM 2017. Spatial and temporal impacts of the alien species Psittacula krameria on the occurrence of avifauna in Gauteng. Honours thesis, University of the Witwatersrand, Johannesburg). There are opportunities for further research projects. Indeed, Ielyzaveta Ivanova ends her discussion with the statement: “this study highlights the need for more research into the potential impacts of the species.”
Rock Dove (Feral Pigeon) Columba livia
Wild Rock Doves in South Africa are derived from escaped domestic birds, a process that would have started in 1652 with the arrival of the first domestic Rock Doves with the Dutch settlers. Wild populations are continually supplemented by escapes from ornamental populations, resulting in a wide variety of colour morphs. Until about 1990 they were confined mainly to the urban and industrial areas of cities, towns and villages. They have subsequently spread into agricultural landscapes; for example, they have largely replaced Speckled Pigeons Columba guinea on dairy farms in the Swartland region of the Western Cape. There are multiple research opportunities.
House Crow Corvus splendens
The House Crow seems to be the only species of the 10 on this list that introduced itself. The ports of East Africa have large populations, and its arrival in the port cities of Durban (around 1970) and Cape Town (early 1990s) is likely to have been of birds that got themselves trapped inside the holds of cargo ships. In both cities there have been massive eradication campaigns. So it is no longer a feasible species to study!
Common Starling Sturnus vulgaris
18 Common Starlings were released by Cecil John Rhodes in Rondebosch, Cape Town, in 1887, about 130 years ago. The range expansion has been reasonably well documented, but it has not been properly reviewed for many decades. Until about 1910, it was confined to the Greater Cape Town region, and then steadily expanded eastwards and, more slowly, northwards. The range expansion has continued into the 21st century. In the two decades between the first and second bird atlases in southern Africa, it has started occurring extensively in KwaZulu-Natal, Free State, Gauteng and Lesotho. Common Starlings have also been introduced to North America, Australia and New Zealand. There has been quite extensive research on the starling in these regions, but all the studies in southern Africa have been descriptive. There are multiple research opportunities.
Common Myna Acridotheres tristis
There were two centres of introduction of Common Mynas to South Africa and different subspecies were involved: the mynas introduced to Durban about 1900 were the subspecies tristoides from Myanmar and adjacent Assam, an Indian state. The mynas introduced to Johannesburg in 1930s were of the nominate subspecies tristis. Of the 10 species considered here, this is the one that is currently expanding its range the fastest. There are multiple resources to describe the range expansion of this species through time, but an authoritative review remains to be written. Apart from some short notes, there are no studies of the biology of Common Mynas in southern Africa. There are multiple research opportunities.
House Sparrow Passer domesticus
The House Sparrows in South Africa are of the Indian subspecies indicus. It seems likely that some of the labourers transported from India in the 1880s and 1890s to work in the sugar-cane fields brought House Sparrows with them as pets. Those that escaped established the feral population. The history of the range expansion up to about 1950 is poorly documented, but it was still largely confined to KwaZulu-Natal. After that the range expansion was explosive over the remainder of South Africa, Namibia, Botswana, Zimbabwe, Mozambique, Zambia, Malawi, Angola and the Democratic Republic of Congo. The impact of the founder population has been enormous. There is a small number of papers on the biology of this introduced species in South Africa, and the opportunities for further studies are large.
Common Chaffinch Fringilla coelebs
Common Chaffinches were one of many bird species introduced by Cecil John Rhodes in the 1890s. The place of introduction was Rondebosch in the Cape Peninsula. In sharp contrast to the Common Starling, it is still confined mainly to the eastern slopes of the mountain range between roughly Rhodes Memorial and Tokai, and the adjacent suburbs. It must be a rare example of a species which has been introduced, and which, after 120 years has neither gone extinct nor expanded its range. Because of the small population size, this is not an easy species to study, but it certainly presents unique opportunities.
Eight of the ten alien bird species in South Africa offer opportunities for interesting research projects.