control against the effects of the larvae of the sphingid moth Nudaurelia cytherea
(Emperor Pine Moth) in pine plantations of Tulbach (1926) and Franschhoek (1941)
(Picker and Griffiths 2011; Skead et al. 2011). There were also likely to be small
populations of feral pigs that escaped from domestic stock throughout the country.
Of particular note is the growth in demand for free-range pork and bacon that is
thought to have resulted in sharp increases in established populations in the Western
Cape (R. van der Walt pers. comm). Feral populations of S. scrofa were assessed as
having Massive environmental impact, and Moderate socio-economic impact, with
the highest summed scores for impacts of any of the mammals assessed by Hagen
and Kumschick (2018). In South Africa, the socio-economic damage reported is
thought to be relatively minor (Spear and Chown 2009a), although concern has been
raised about their impacts on the threatened Psammobates geometricus (Geometric
Tortoise) and some rare geophytes, prompting a control programme in Porseleinberg
and Kasteelberg. To date, 1209 feral pigs have been removed, with the population
from Kasteelberg coming close to extirpation (van Wilgen and Wilson 2018). In
terms of the NEM:BA Alien and Invasive Species Regulations (hereafter “the
Regulations”), the species is listed in context of specific sites.
5.3.2 Felis catus (Domestic Cat)
Domestic Cats have been introduced around the world, and are one of the highest
impact invasive vertebrate predators (Hagen and Kumschick 2018). Their introduction to South Africa probably coincided with early ships and the rodents that came
with them (see below). Some authors distinguish between feral cats, strays and
domestic cats (Dickman 2009), but here we treat them together, as they are often
in continuum and their impacts on the environment appear similar. While the impact
of cats is undoubtedly highest on island fauna (Chap. 8, Greve et al. 2020;
Courchamp et al. 1999), they have also resulted in the extinction of continental
land birds (Dickman 2009). Estimates of predation rates have varied greatly and
mostly consist of prey carried to the owners’ homes. But video cameras fitted to
collars suggest that cats each kill 2–5 small animals per week, with only a quarter of
prey items taken home, half of prey items are left in the field and the remainder eaten
(Loyd et al. 2013). The density of cats in urban areas is estimated to be typically
around 400 cats/km
2 (in the UK, Sims et al. 2008). Densities of cats in Cape Town
have been estimated as 80–300 cats/km
2 , and are thought to be lower due to the
existence of numerous small carnivores (Caracal, Caracal caracal, mongooses, and
some birds of prey) which are thought to control their numbers (F Morling
unpublished data; George 2010; Peters 2011). In a South African urban conservancy
(in KwaZulu-Natal) the density of cats was found to be between 23 and 40 cats/km
2 ,
with densities likely augmented by supplemental feeding (Tennent and Downs
2008). Despite regular meals for most cats in Cape Town’s suburbs (estimated
density of cats 150 cats/km
2
), their kill rates estimated using kitty cams, suggest
that annual kills might be as high as 26 million animals, composed of 42% small
5 Terrestrial Vertebrate Invasions in South Africa
121
(Emperor Pine Moth) in pine plantations of Tulbach (1926) and Franschhoek (1941)
(Picker and Griffiths 2011; Skead et al. 2011). There were also likely to be small
populations of feral pigs that escaped from domestic stock throughout the country.
Of particular note is the growth in demand for free-range pork and bacon that is
thought to have resulted in sharp increases in established populations in the Western
Cape (R. van der Walt pers. comm). Feral populations of S. scrofa were assessed as
having Massive environmental impact, and Moderate socio-economic impact, with
the highest summed scores for impacts of any of the mammals assessed by Hagen
and Kumschick (2018). In South Africa, the socio-economic damage reported is
thought to be relatively minor (Spear and Chown 2009a), although concern has been
raised about their impacts on the threatened Psammobates geometricus (Geometric
Tortoise) and some rare geophytes, prompting a control programme in Porseleinberg
and Kasteelberg. To date, 1209 feral pigs have been removed, with the population
from Kasteelberg coming close to extirpation (van Wilgen and Wilson 2018). In
terms of the NEM:BA Alien and Invasive Species Regulations (hereafter “the
Regulations”), the species is listed in context of specific sites.
5.3.2 Felis catus (Domestic Cat)
Domestic Cats have been introduced around the world, and are one of the highest
impact invasive vertebrate predators (Hagen and Kumschick 2018). Their introduction to South Africa probably coincided with early ships and the rodents that came
with them (see below). Some authors distinguish between feral cats, strays and
domestic cats (Dickman 2009), but here we treat them together, as they are often
in continuum and their impacts on the environment appear similar. While the impact
of cats is undoubtedly highest on island fauna (Chap. 8, Greve et al. 2020;
Courchamp et al. 1999), they have also resulted in the extinction of continental
land birds (Dickman 2009). Estimates of predation rates have varied greatly and
mostly consist of prey carried to the owners’ homes. But video cameras fitted to
collars suggest that cats each kill 2–5 small animals per week, with only a quarter of
prey items taken home, half of prey items are left in the field and the remainder eaten
(Loyd et al. 2013). The density of cats in urban areas is estimated to be typically
around 400 cats/km
2 (in the UK, Sims et al. 2008). Densities of cats in Cape Town
have been estimated as 80–300 cats/km
2 , and are thought to be lower due to the
existence of numerous small carnivores (Caracal, Caracal caracal, mongooses, and
some birds of prey) which are thought to control their numbers (F Morling
unpublished data; George 2010; Peters 2011). In a South African urban conservancy
(in KwaZulu-Natal) the density of cats was found to be between 23 and 40 cats/km
2 ,
with densities likely augmented by supplemental feeding (Tennent and Downs
2008). Despite regular meals for most cats in Cape Town’s suburbs (estimated
density of cats 150 cats/km
2
), their kill rates estimated using kitty cams, suggest
that annual kills might be as high as 26 million animals, composed of 42% small
5 Terrestrial Vertebrate Invasions in South Africa
121