Bonn. Despite their exotic appearance and origin, they have become an integral part of the cityscape: animal species that were previously unknown to Bonn such as the ring-necked parakeet have become native. This can pose some risks.
They've been abandoned, smuggled in, or they've busted out. Some animals not indigenous to the area came into Bonn and the region years ago, multiplied and eventually became native. In some cases this has had negative consequences for the native animal population and the vegetation. But the fight against invasive species is expensive. Experts from the Landesinstitut für Umwelt, Messungen und Naturschutz (LUBW) (State Institute for the Environment, Measurements and Nature Conservation) say that action is therefore only taken where there is a risk of particularly serious damage to property or health.
The ring-necked parakeet
The ring-necked (or rose-ringed) parakeet can be found especially on the island of Grafenwerth, in the Rhineaue park, near the North Bridge and in Bonn-Tannenbusch. Originally, they existed only in subtropical areas of Africa and Asia. In the 1960’s, wild specimens were sighted for the first time in Cologne. They have mainly grown in the region from Duisburg to Bonn. "Presumably, the animals escaped or were abandoned," says Till Töpfer, head of ornithology at the Koenig Museum.
The birds are striking because of their green feathers and long tails. They are frequently underway in groups, in particular in the winter, the animals form sleeping-communities. The ring-necked parakeets like to live in woodpecker burrows. However, the feared rivalry over food and tree hollows have so far failed to materialize. "Although there are now an estimated 5,000 birds, they do not compete with native birds," says Töpfer. Should the birds become a problem in the future, hunting would be the only way to control them.
Ring-necked parakeets represent more of a disturbance for people than for other animals as they are a source of both noise and filth. According to a German organization that specializes in birds, there have been more than 1,300 sightings of ring-necked parakeets in Bonn in the last five years.
North American crayfish
Calico crayfish originates from North America, probably imported in 1993 by soldiers of the Canadian Airbase. In contrast to the ring-necked parakeet, this crayfish causes enormous damage to the native species, since the crayfish has increased more or less uncontrollably since then. As a result, native crayfish and dragonflies are displaced and smaller bodies of standing and running water are damaged. The North American calico crayfish also multiplies so explosively because it can reproduce in extremely short cycles and huge numbers.
A program was launched in NRW in 2004 to protect two native river crayfish species. The North American crayfish can transmit a disease which is fatal to the native species. Researchers estimate that the number of calico crayfish is now "in the millions" and it will hardly be possible to stop it.
They have become an established part of the animal world in Rheinaue park - and yet the semiaquatic rodents from South America are less well known and therefore more unpredictable than ducks or swans.
The animals have spread considerably. "In nine years the numbers have doubled in the areas surveyed," said Torsten Reinwald, spokesman for the German Hunting Association (DJV) in Berlin. According to the DJV, the experts of the Wild Animal Information System of the German Federal States (WILD), the main reason for the increase is the persistently mild winters.
Problematic is that the water rodents are not shy, says Christian Montermann, scientist at the Koenig Museum. Too much close proximity, for example by feeding, "makes the Nutria lose their timidity and the distance between them and the walkers becomes smaller and smaller. Of course, this can also lead to bites." Having three litters per year ensures that Coypu multiply quickly. Responsible authorities explicitly oppose regular hunting of the Nutria, as they do not yet have a massive impact on the native flora and fauna, but still the animals remain an invasive species.
"The environment suffers when wild animals are fed food. Sediment layers form on the bottom of the Rheinaue lake, the water quality decreases and ultimately the lake water is threatened because of algae growth," explains the environmental office in Bonn. This has happened several times in recent years. However, the feeding ban does not only apply to Nutria, in general no wild animals should be fed.
North American bullfrog
The bullfrog originates from North America and was sighted 17 years ago in man-made lakes in southern Germany and at the Rhine. The North American bullfrog helps to displace masses of indigenous amphibians. It is hunted every year because it had almost completely ousted the native species. Eggs are also collected to prevent further spread.
Many hundreds of bullfrogs and tens of thousands of tadpoles can still be found in some regions. "I doubt that we will be able to control it completely," says Kai Höpker of a state environmental institute (LUBW). According to the LUBW, they are also occasionally seen in Bonn and the region. A few years ago, there was a significant campaign against the bullfrog population in Meckenheim.
(Orig. text: Nathalie Dreschke, Translation: Carol Kloeppel)