Land-use changes and monk parakeet expansion in the Pampas grasslands of Argentina

Aim The monk parakeet, Myiopsitta monachus (Boddaert, 1783), is a successful invasive species that has established viable populations on four continents, including North America and Europe. Of particular interest is the little known, large-scale expansion of monk parakeet within its native range on the Pampas grasslands of Argentina during the 20th century. To understand the key factors involved in this large-scale expansion and their implications in terms of current hypotheses on bird introductions, we investigated in detail the expansion process and related changes in land use during the period 1860-2010. Location The Pampas grassland ecoregion of Argentina. Methods Range expansion was assessed using the following information sources: museum specimens, published scientific literature, reports from government agencies, postal questionnaires, internet public media, and data obtained during extensive travelling by the authors. Results The range of the monk parakeet has expanded by about 327,958km(2) in 150years. The linear range expansion rate was between 2.1 and 7.6kmyear(-1). Range expansion followed a neighbourhood diffusion pattern. Key land-use changes included expansion of eucalyptus trees (the preferred nesting tree), introduction of European cattle, weed (thistle) invasion, conversion of grassland to cropland, and urban development. Main conclusions Eucalyptus was a key factor favouring parakeet range expansion. Food availability increased as a result of changes in grassland structure, weed invasion and cropland expansion. Urban environments operated as expansion stepping stones along the routes of railways. The invasive potential of monk parakeet and other parrots appears to be related to behavioural flexibility and dietary opportunism favoured by high intelligence and morphological adaptations (beak and foot structure).