Nest cavity characteristics, reproductive output and population trend of naturalised Amazon parrots in Germany

Although many parrot species are decreasing in their native range, introduced parrot populations can be found in urban areas around the globe. We thus need to understand how they adapt to this novel environment and to assess the possibility of a range expansion that might threaten native species. We studied population growth, nest site requirements, as well as limiting factors like reproductive output and mortality of the only European population of Yellow-headed Parrots (Amazona oratrix) in the city of Stuttgart, southwest Germany, to assess the risk of a possible range expansion. Although offspring could be seen on a regular basis, parrot numbers hardly increased during the last 5 years (51 individuals in spring 2015, including 12 breeding pairs). Ten accessible nest cavities were studied in detail: they were located exclusively in large, old London Plane (Platanus × acerifolia) trees in an area of less than 1 km2 in the city’s public parks and were at least 65 cm deep. Average reproductive output was 1.3 fledglings/pair, which is high in comparison to data from birds in their native range. Mortality, especially of young parrots, appears to be high due to risks in urban areas such as collisions with vehicles and windows and could partly explain slow population growth. This slow population growth in combination with the need for sufficiently large nest cavities may hinder a range expansion of this species in future years.