The population dynamics of two invasive bird species belonging to two different bird families have been studied, one belonging to the Columbidae family and the other to the Psittacidae family, both phylogenetically distant but jointly occupying some urban habitats in Western Europe. Different information tools were used through bibliographic reference software available on the web. The main conclusions are as follows: the fundamental mechanics of the invasion of these two species consist of their genetics, and their environmental resistance predicts that the current patterns of spread are better than the climate in general habitats and in urban habitats in particular. One of the most fundamental aspects of their invasive processes is of a genetic nature.