Invasive alien species in Switzerland - Schweizer ...

2 > Vertebrates – Vertebrata 37
The only introduced squirrel is the Siberian chipmunk (Tamias sibiricus (Laxmann)).
It was released into parks in Genève by pet lovers and established a small but stable
population (Long, 2003). Its native distribution covers a large part of northern Asia and
it is expanding its range westwards, and arrived in Finland in recent years (Grzimek,
1975). This small beautiful squirrel is frequently kept as a pet and has escaped or been
deliberately introduced in several European countries. In Switzerland only one small
colony is known, but it has also established populations in Freiburg im Breisgau in
Germany and in Italy (Personal observation; Andreotti et al., 2001). In Russia it is
known to destroy half the average forest nut production and cause great damage to
grain crops. Since the chipmunks mainly feed on the ground, they can severely affect
crops and also damage gardens and orchards (Long, 2003). A Belgian study, which
compared the abundance of birds in areas with and without the alien squirrel, concluded
that T. sibiricus has no impact on bird populations (Riegel, 2001). In most of
Europe, released populations have not increased and spread significantly, and it seems
that the Siberian chipmunk is dependent on a rich food source, as it is most often found
in parks and graveyards with a variety of different plant species (Krapp, 1978a, b).
Thus, it should be regarded as a species with a low invasion potential. However, the
release of pet animals should be of great concern and should probably be better regulated.
In particular, the danger of diseases carried by alien pets to wildlife, other pets
and humans should not be underrated, as demonstrated by the recent arrival of diseases
with introduced pet rats from Africa to the USA.
Another squirrel species, although one that has not yet arrived in Switzerland, is of
great concern, as it is established in Italy and spreading. The grey squirrel (Sciurus
carolinensis Gmelin) (see Fact Sheet) is one of the rare cases where the impact on a
native congeneric species, i.e. the red squirrel (Sciurus vulgaris L.), is well documented.
In Great Britain, except for some mountainous conifer forests, the red squirrel
has been replaced completely by the grey squirrel. Today, the population in northern
Italy is rapidly expanding its range and threatens to invade Switzerland in the next 20
years or so. Swiss authorities should follow the expansion closely and put prevention
methods in place to stop or delay the spread at the border. Whereas the invasion into
the Ticino is more imminent, the modelled expansion of the grey squirrel to France is
of greater concern, as from here it can expand into Switzerland around Genève. Moreover,
if isolated populations outside the invasion front are encountered, they should be
eradicated as long as they are small. Swiss authorities should also initiate discussion
with Italian authorities to implement the approved action plan to eradicate the species
in the Italian part of the Ticino valley.
The re-introduction of beavers in some countries has been problematic in the past. In
some areas, at least in Austria and Finland and perhaps Germany (Geiter et al., 2002),
the American congeneric Castor canadensis Kuhl was introduced instead of the European
beaver (C. fiber L.) (Freye, 1978; Englisch, 2002). These two species are very
similar and indeed were considered to be one species until recently, but the karyotypes
differ. No further introductions of the American species should be made in Europe. The
introductions of C. fiber of different origins within Europe seem to be of less concern
in many parts, since the species is genetically relatively uniform, with only a few