Neotropical austral migrant landbirds: Population trends and habitat use in the central Monte desert, Argentina

We studied density changes of two groups of Neotropical austral migrant landbirds-the South American temperate-tropical (SATT) and cold-temperate (SACT) migratory systems-in the main habitat types of the central Monte desert of Argentina (open Prosopis flexuosa woodland and Larrea cuneifolia shrubland) over 10 years. Five species, all tyrant flycatchers (Tyrannidae) made up SATT, whereas only two of the seven species of SACT were tyrannids. Densities of both SATT and SACT were higher in open woodland than in shrubland. SATT density did not differ among years, but SACT density did, having lower values in 1994 in both habitats. In subsequent years, SACT densities increased but did not reach values similar to those previous to 1994. The decline in 1994 coincided with a two-year drought period that began in 1993, but lower density in the following years did not appear to be related to climatic conditions in the study area, suggesting a low capacity of SACT species to recover population abundance after periods of stress. In contrast, SATT density was not associated with local climatic conditions, possibly because several SATT species used the study area only as a stopover site. During the breeding season, birds of both migratory systems disproportionately use the open woodland, which offers more sites to nest and feed than does the shrubland. Although most SATT and SACT species are abundant and not currently of conservation concern, human activities in the central Monte desert promote the structural simplification of the habitat, which could threaten future populations of Neotropical austral migrant landbirds in this ecosystem.