Alien opportunities: 10 bird species with feral populations in South Africa

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

The small black mark on the top of the bill indicates that these are hybrids between Mallard and Yellow-billed Duck. This photograph was taken by AP Labuschagne at Lamberts Bay, in the northwest corner of the Western Cape. See http://vmus.adu.org.za/?vm=BirdPix-40550 for more detail of this record. This is one of 44 records of Mallards and Mallard-hybrids in the BirdPix section of the Virtual Museum. Some of the hybrids are quite bizarre in appearance; see for example:  http://vmus.adu.org.za/?vm=BirdPix-47425

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

These Chukar Partridges were in the village on Robben Island.  See http://vmus.adu.org.za/?vm=BirdPix-2108 for more detail of this record. This is one of 13 records of this species in the BirdPix section of the Virtual Museum. All are from Robben Island.

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

This Common Peacock was photographed by Zenobia van Dyk on a farm in the Eastern Cape. From her description, this bird is probably semi-feral. See http://vmus.adu.org.za/?vm=BirdPix-54818. There are 29 records of Common Peacock in the BirdPix section of the Virtual Museum

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.

This is the SABAP2 distribution map for the Common Peacock on 23 December 2018. Many of the records would be of semi-feral peacocks, but it is nevertheless remarkable in how many “pentads” peacocks have been recorded by the bird atlas citizen scientists. There is a full description of the methods used by the Second Southern African Bird Atlas Project in this paper The fundamentals of the SABAP2 protocol, and an explanation of the interpretation of this map in a paper entitled Pentad scale distribution maps for bird atlas data.

Rose-ringed Parakeet Psittacula krameri

There are 20 records of Rose-ringed Parakeet in the BirdPix section of the Virtual Museum. Four of these are from the area of Africa in which it occurs naturally: Sudan, Nigeria, Ghana and Senegal. There are 15 photographic records of alien parakeets in South Africa: 11 from Gauteng, four records from KwaZulu-Natal, and one from the Western Cape. These two birds were recorded by Anthony Paton in the Randburg-Roodepoort region of Johannesburg. See http://vmus.adu.org.za/?vm=BirdPix-43335.

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

There are 70 records of Rock Dove in the BirdPix section of the Virtual Museum. This bird was feeding close to a road at Mouille Point, Cape Town. http://vmus.adu.org.za/?vm=BirdPix-57236.

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.

The bird atlas distribution map for the Rock Dove. The pentads shaded dark blue have the largest reporting rates. The clusters of dark blue pentads are concentrated on the cities of South Africa. Downloaded from the SABAP2 website on 23 December 2018.

House Crow Corvus splendens

There are 15 records of House Crow in the BirdPix section of the Virtual Museum. Most of them are from port cities and towns along the Indian Ocean coast of Africa: from  north to south, Lamu, Mombasa, Zanzibar, Dar es Salaam, Beira, Maputo and, finally, … Durban. The late Rob Dickinson, whose photo this is, was a remarkable citizen scientist, and this House Crow, welcoming Rob to Tanzania at Das es Salaam Airport was selected to celebrate his memory. He made contributions to the Virtual Museum from all over Africa. More details of this record are at http://vmus.adu.org.za/?vm=BirdPix-21374.

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

There are 116 records of Common Starling in the BirdPix section of the Virtual Museum. This is the first and only record from Gauteng, taken by Kevin Lavery on 13 June 2015, near Vereeniging along the Vaal River. Details at http://vmus.adu.org.za/?vm=BirdPix-65734.

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

This image was selected from the 96 Common Mynas available in the Virtual Museum because it is the only one beyond South Africa’s borders. Samantha Venter took this photo in Gaborone, Botswana. Full details at http://vmus.adu.org.za/?vm=BirdPix-22063.

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.

This is the “range-change” map for the Common Myna in South Africa, Lesotho and Swaziland. It shows how the range of the species changed in the quarter century between the two bird atlas projects. There is a full description of the algorithm used to produce this map, and its interpretation, in a paper in the ejournal Biodiversity Observations called Displaying changes in bird distributions between SABAP1 and SABAP2. In summary, the grid cells for which there is enough data to take a decision are shaded in one of six colours: blue,  dark green, light green, yellow, orange or red. Blue and red are the extremes; under a set of assumptions, they mean that a three-fold increase/decrease respectively has occurred in the grid cell between the two projects. For the Common Myna there has clearly been a massive increase in abundance since SABAP1. In parts of KwaZulu-Natal, the core of the SABAP1 range, there appears to have been large decreases in abundance. This observation needs confirmation by fieldwork.

House Sparrow Passer domesticus

This male House Sparrow was photographed by John Fincham near the village of Kliprant in the arid Knersvlakte of the Western Cape. See http://vmus.adu.org.za/?vm=BirdPix-18523 There are a total of 212 records of the species in the BirdPix section of the Virtual Museum.

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.

The SABAP2 distribution map for the House Sparrow, 23 December 2018. It is recorded in most places in South Africa where there is human habitation, even in arid regions. For example, in the Kruger National Park in the northeast, the only human habitations are the tourist rest camps, and these are the places  with House Sparrows there. There is a full description of the methods used by the Second Southern African Bird Atlas Project (SABAP2) in this paper The fundamentals of the SABAP2 protocol, and an explanation of the interpretation of this map in a paper entitled Pentad scale distribution maps for bird atlas data.
This is the “range-change” map for the House Sparrow in South Africa, Lesotho and Swaziland. It shows how the range of the species changed in the quarter century between the two bird atlas projects. There is a full description of the algorithm used to produce this map, and its interpretation, in a paper in the ejournal Biodiversity Observations called Displaying changes in bird distributions between SABAP1 and SABAP2. In summary, the grid cells for which there is enough data to take a decision are shaded in one of six colours: blue,  dark green, light green, yellow, orange or red. Blue and red are the extremes; under a set of assumptions, they mean that a three-fold increase/decrease respectively has occurred in the grid cell between the two projects. For the House Sparrow, in total contrast  to the Common Myna, above, there is almost a jumble of colours since SABAP1, with very little patterning. Within this region, there have been no new areas colonized since SABAP1, and at a local scale, there have been fluctuations in population size.

Common Chaffinch Fringilla coelebs

Marna Buys photographed this Common Chaffinch in the Kirstenbosch National Botanical Gardens, within a few kilometres of where the founder population was released. There are 12 records in the BirdPix section of the Virtual Museum. This one is curated at http://vmus.adu.org.za/?vm=BirdPix-61052.

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.

Wrap up

Eight of the ten alien bird species in South Africa offer opportunities for interesting research projects.

Les Underhill
Les Underhill
Prof Les Underhill has been Director of the Animal Demography Unit (ADU) at the University of Cape Town since it started in 1991. Although citizen science in biology is Les’s passion, his academic background is in mathematical statistics. He was awarded his PhD in abstract multivariate analyses in 1973 at UCT and what he likes to say about his PhD is that he solved a problem that no one has ever had. He soon grasped that this was not the field to which he wanted to devote his life, so he retrained himself as an applied statistician, solving real-world problems.