Dispersal relies on the presence of alien trees, especially pines (Pinus) and oaks
(Quercus), which were earlier historical introductions (Richardson et al. 2020,
Chap. 3). The natural dispersal of these animals was facilitated by deliberate
movements by people into Swellendam and Ceres (see Smithers 1983). By 1920,
the Cape Provincial Government recognised squirrels as vermin, paying three pence
per head (Skead et al. 2011). Squirrels can reach high densities in urban settings with
10–50 per ha in their native areas (Parker and Nilon 2008). Socio-economic impacts
of squirrels include damage to pine nut crops, vegetable and fruit crops, and even
telephone cables (JM pers. obs.). Most of the impacts of squirrels are thought to be
socio-economic, but their sub-lethal and indirect effects on avifauna may be substantial (Bonnington et al. 2013), as they are known nest predators (Hewson et al.
2004). Today, squirrels are revered by many members of the public, and they are
only recognised by the Regulations in specific contexts (in association with fruit
farming).
5.4 Aves
5.4.1 Invasive Birds in South Africa
There are at least 92 alien bird species that have been introduced to South Africa,
with only a minority having become established (n ¼ 18) or invasive (n ¼ 14) (van
Wilgen and Wilson 2018). A suite of birds were introduced to South African towns
by European colonists of the eighteenth and nineteenth centuries, seeking to make
their surroundings more familiar, as colonists did in many temperate parts of the
world (Long 1981; van Rensburg et al. 2011; Duncan et al. 2003).
In South Africa, invasive birds are unusual in all being strongly commensal with
humans, without viable populations in natural ecosystems (Richardson et al. 2011b).
The spread of native birds into novel (especially urban) areas is not explicitly
covered in this chapter (but see Potgieter et al. 2020, Chap. 11), but the success of
some species is notable as it is based on the modifications associated with agricultural and urban environments (Symes et al. 2017).
For example, Cattle Egrets, Bubulcus ibis, and the Blacksmith Lapwing, Vanellus
armatus, both arrived in the Cape in the 1930s. Hadeda Ibis, Bostrychia hagedash,
expanded into the Cape Region in the 1980s (Macdonald et al. 1986), and their
population has grown considerably as trees and lawns have proliferated in
urbanising areas of a biome which is otherwise largely free of trees and grasses
(Duckworth et al. 2010, 2012; Singh and Downs 2016). Urbanisation has been found
to have a homogenising effect on the avian fauna of South African cities, with both
native and alien birds increasing in density as a result of alien species (van Rensburg
et al. 2009).
5 Terrestrial Vertebrate Invasions in South Africa
129
(Quercus), which were earlier historical introductions (Richardson et al. 2020,
Chap. 3). The natural dispersal of these animals was facilitated by deliberate
movements by people into Swellendam and Ceres (see Smithers 1983). By 1920,
the Cape Provincial Government recognised squirrels as vermin, paying three pence
per head (Skead et al. 2011). Squirrels can reach high densities in urban settings with
10–50 per ha in their native areas (Parker and Nilon 2008). Socio-economic impacts
of squirrels include damage to pine nut crops, vegetable and fruit crops, and even
telephone cables (JM pers. obs.). Most of the impacts of squirrels are thought to be
socio-economic, but their sub-lethal and indirect effects on avifauna may be substantial (Bonnington et al. 2013), as they are known nest predators (Hewson et al.
2004). Today, squirrels are revered by many members of the public, and they are
only recognised by the Regulations in specific contexts (in association with fruit
farming).
5.4 Aves
5.4.1 Invasive Birds in South Africa
There are at least 92 alien bird species that have been introduced to South Africa,
with only a minority having become established (n ¼ 18) or invasive (n ¼ 14) (van
Wilgen and Wilson 2018). A suite of birds were introduced to South African towns
by European colonists of the eighteenth and nineteenth centuries, seeking to make
their surroundings more familiar, as colonists did in many temperate parts of the
world (Long 1981; van Rensburg et al. 2011; Duncan et al. 2003).
In South Africa, invasive birds are unusual in all being strongly commensal with
humans, without viable populations in natural ecosystems (Richardson et al. 2011b).
The spread of native birds into novel (especially urban) areas is not explicitly
covered in this chapter (but see Potgieter et al. 2020, Chap. 11), but the success of
some species is notable as it is based on the modifications associated with agricultural and urban environments (Symes et al. 2017).
For example, Cattle Egrets, Bubulcus ibis, and the Blacksmith Lapwing, Vanellus
armatus, both arrived in the Cape in the 1930s. Hadeda Ibis, Bostrychia hagedash,
expanded into the Cape Region in the 1980s (Macdonald et al. 1986), and their
population has grown considerably as trees and lawns have proliferated in
urbanising areas of a biome which is otherwise largely free of trees and grasses
(Duckworth et al. 2010, 2012; Singh and Downs 2016). Urbanisation has been found
to have a homogenising effect on the avian fauna of South African cities, with both
native and alien birds increasing in density as a result of alien species (van Rensburg
et al. 2009).
5 Terrestrial Vertebrate Invasions in South Africa
129