Аннотация:Human-mediated changes in land-use have affected many bird species in South America, and other regions where agroecosystems are now the most common environments. We evaluate how the rarity of landbird species in agroecosystems is influenced by their specialisation in nesting habitat. We estimated rarity of species by their local abundance and area of occupancy in the Pampas of Argentina. Relative local abundance was positively associated with area of occupancy. Most rare species (9 of 14) were specialists, whereas 15 of the 21 common species were generalists. Both woodland and grassland specialists had smaller areas of occupancy than generalist species. This pattern was expected for woodland specialists, owing to a lack of woodland in the agroecosystems of the Pampas. In the case of grassland specialists, the pattern might reflect the destruction of natural grasslands owing to an increase of agriculture. Wetland specialists were an exception within specialists, probably because they share characteristics with common species, such as flocking behaviour and use different feeding habitats. Our results show that some grassland species of increased conservation concern in the Pampas are facing the threat of extinction associated with low local abundance and limited distribution, emphasising the need for further conservation effort
