Temporal fluctuations in raptor abundances in grasslands of southeastern South America

Abstract

We conducted 44 roadside surveys on grasslands landscapes of southern Brazil and Uruguay to study temporal changes in raptor abundance. Each route was surveyed twice in fall/winter and twice in spring/summer. Raptor abundance was higher during summer than winter, but did not differ between years. Thirteen of the 33 species recorded showed temporal changes in abundance, or are known to be migrants in the region. White-tailed Kite (Elanus leucurus), Yellow-headed Caracara (Milvago chimachima) and Southern Caracara (Caracara plancus) had higher abundance during fall/winter than spring/summer, which might be attributed to nomadic movements in agricultural landscapes. Changes in abundance of Savanna Hawk (Buteogallus meridionalis) and American Kestrel (Falco sparverius) suggest irruptive or nomadic movements. Turkey Vulture (Cathartes aura), Snail Kite (Rostrhamus sociabilis) and White-tailed Hawk (Geranoaetus albicaudatus) were more abundant in spring/summer than fall/winter, and our results suggest that they are partial migrants in the region. Variations in temperature, water level, and land use in agro-environment as well as dispersion, recruitment, and ephemeral concentration of food resources probably are the causes of fluctuation observed. Our results provide a starting point to better understand raptor temporal fluctuations and abundance in southeastern South America, but further investigations are required. © 2014 The Raptor Research Foundation, Inc.