Invasive alien species in Switzerland - Schweizer ...

2 > Vertebrates – Vertebrata 47
The introduction of North American ruddy duck (Oxyura jamaicensis (Gmelin)) (see
Fact Sheet) into Europe led to one of the best-known cases of concern about an alien
species in relation to conservation of a globally threatened native species, i.e. the
white-headed duck (Oxyura leucocephala Scopoli)), classified as Vulnerable by IUCN
(the World Conservation Union) (Hughes et al., 1999). The two species readily hybridize
and it is likely that unless counter-measures are taken the white-headed duck population
will be completely absorbed. A European action plan for eradication of the
destructive invader has been set up to safeguard the small populations of white-headed
duck in the western and eastern Mediterranean. The plan does not cover Asia, but it is
to be hoped that the ruddy duck will be eradicated in continental Europe and considerably
reduced in the UK, so that its spread to Asia becomes unlikely. The spread of
the ruddy duck within the UK and then through Europe was facilitated by the fact that
it is a migratory species. While the ‘Action Plan for the White-headed Duck’ (Green
and Hughes, 1996) names eight threats and limiting factors, the introduction of the
ruddy duck is the only one that is considered critical for its implementation. Tragically
the white-headed duck population was just recovering in Spain, from a minimum of 22
birds in 1977 to about 2,700 today due to a conservation programme, but it is now
being hit by hybridization with the ruddy duck. Over 4,200 ruddy ducks have now been
shot in the UK, where shooting at large wintering sites is crucial to the success of the
action plan. Switzerland has endorsed the eradication plans and agreed to take action
against the ruddy duck within its borders. Shooting of the ruddy duck has to be conducted
in a co-ordinated way by hunting and conservation authorities. Firstly, the
correct identity has to be confirmed, since the two Oxyura species can be very similar.
It is clear from the current situation that ruddy ducks thrive in Europe, build up large
viable populations, and spread rapidly. Therefore, keeping ruddy ducks in captivity
needs to be regulated. While the ultimate goal for such a serious problem species is the
prohibition of keeping them in captivity, an interim measure should be the monitoring
of all specimens kept and acceptance of collections only in secure facilities.
In Europe several parrot species frequently escape from captivity and some of those are
able to establish in the wild under favourable conditions. Most of these colonies are in
parks in cities, where a rich food source of fruit-bearing trees and bird feeders during
the harsh winter time together with temperatures on average 2° C above the surrounding
landscape allow their survival. The climate seems an important factor for these
species that naturally inhabit lower latidudes. The most common parrot species are the
rose-ringed parakeet (Psittacula krameri (Scopoli)) and the monk parakeet (Myiopsitta
monachus (Boddaert)), which have established large colonies in several European
cities, including some in neighbouring countries: France, Germany, Austria and Italy.
There are single reports of breeding attempts of both species in Switzerland. They are
apparently limited to city environments and it is not known whether there is any genetic
exchange between the colonies in Europe. The colonies are probably isolated and
will not spread that far. The rose-ringed parakeet nests in tree cavities, so that it will
compete with native wildlife. The monk parakeet is unusual, building large communal
nests on trees, buildings and power pylons. In their home ranges both species are
recognized as agricultural pests. Other parrot species are found irregularly throughout
Europe. Any parrots encountered in the wild in Switzerland should be captured.