Habitat use by Swainson's Hawks on their Austral wintering grounds in Argentina

We examined the use of agricultural habitats by Swainson's Hawks' (Buteo swainsoni) in La Pampa and Santa Fe provinces, Argentina. We found an association of foraging Swainsons' Hawks with permanent pastures such as fallow, natural, and alfalfa fields. The hawks also used plowed fields for sunning, resting, and preening. Fields planted with annual crops and pastures were used very little, except when they were cut for hay, plowed, and harvested, or when low crop height and cover allowed the hawks to land in fields. The availability of abundant, yet widely-spaced and transient food-sources, such as insect outbreaks, appeared to be the principal factor influencing habitat use by the hawks. Their reliance on agricultural habitats makes Swainson's Hawks highly vulnerable to pesticide contamination and has contributed to the occurrence of significant mortality events on their wintering grounds.