Observation of Diurnal Soaring Raptors In Northeastern Brazil Depends On Weather Conditions and Time of Day

Abstract Weather conditions influence flight performance of soaring raptors, which take advantage of the strength of rising air currents to travel and forage. Most studies on soaring raptors are not conducted when precipitation and fog are present or during the hottest times of the day, when it is expected that these factors reduce species' detectability. The effect of weather on the movement of migratory birds has been studied extensively, but few studies have addressed these effects on nonmigratory tropical raptors. We described the richness, composition, and activity patterns of a diurnal soaring raptor community and we identified how daily weather conditions affected the probability of observing a species. For 11 mo, we surveyed five fixed points in an Important Bird and Biodiversity Area consisting mainly of montane Atlantic Forest in northeastern Brazil, for a total of 98 point counts. We recorded 12 species of soaring raptors, of which five made up 88% of all sightings. We added new records for three soaring raptor species, updating the previous richness list for the study region to 26 species. Daily wind velocity positively influenced the probability of observing Short-tailed Hawks (Buteo brachyurus). Daily relative humidity positively influenced the probability of observing Mantled Hawks (Pseudastur polionotus) and negatively influenced that of Roadside Hawks (Rupornis magnirostris). Six species would not have been recorded if afternoon samplings were not made. We demonstrated the need to consider weather conditions and time of day to increase the chance of observing diurnal soaring raptors.