In our modern globalized world more and more organisms are transported across the world and consequently more and more organisms are able to establish themselves outside their original distribution area. It is commonly known that some of these exotic species could have an enormous ecological and economical impact, but generally the knowledge necessary to make a statement about the potential expansion and impact of an established alien is lacking. The aim of this project is to make a scientific evaluation of the potential spread and impact of explosive increasing exotic species. This will be done using the Ring-necked Parakeet (Psittacula krameri), a cavity nesting bird from India and Afrika that was introduced in several European cities. By linking several parakeet-dataset with geographical data and habitat records, an 'ecological profile' of the parakeet will be made. By means of this ecological profile, a potential habitat map will be produced. I will also estimate at what rate the parakeet might occupy the suitable habitat. By analyzing the number of parakeets, the number of native cavity nesting birds and habitat characteristics I will present an 'impactrelation' for the effect of competition for cavities. By applying this impactrelation on the predicted parakeet expansion, I will be able to predict the effect of the Ring-necked Parakeet on the populations of native cavity nesting birds.