Raptor population trends in northern Botswana: A re-survey of road transects after 20 years

摘要

Across Africa, many raptor species, especially vultures, are in steep decline. Botswana is regionally important for numerous raptor species including vultures, but recent population trends of raptors within this country are totally unknown. In 2015-2016 we repeated road transects for raptors across northern Botswana that were first conducted in 1991-1995. In total, we re-surveyed 20,712 km of transects. From these data we explored changes in abundance of 29 species. Fourteen species (48%) showed significant declines. Of these, 11 species declined by & 50% and three species declined by 37-50%. Non-significant declines of & 70% were shown for four species, of 30-65% for six species and of & 10% for a further two species. In contrast only three species, all large eagles - tawny eagle (Aquila rapax), brown snake eagle (Circaetus cinereus) and black-chested snake eagle (Circaetus pectoralis), showed significant but small increases of between 6 and 15%. For most species, population trends were similar both inside and outside of protected areas, with only two species showing significantly different trends. Declines of bateleur eagle (Terathopius ecaudatus) were lower inside protected areas. In contrast, brown snake eagles showed stable populations inside protected areas but large increases outside of protected areas. These re-surveys suggest extremely worrying trends for multiple raptor species in Botswana, and highlights the benefit of repeating historical surveys to understand population trends in countries that lack systematic monitoring of wildlife populations.