A two-year project in collaboration with the conservation NGO Raptors Botswana has confirmed researchers’ fears that many birds of prey are fast disappearing from one of Africa’s great wild landscapes. The project repeated a famous bird survey conducted over 20 years ago, by driving over 20 000km in a 4×4 across Botswana.
Reported sightings of iconic species of eagles and vultures declined by as much as 80% compared with the previous survey, while some migrant species have since vanished, according to the study published in the international scientific journal Biological Conservation.
The researchers returned to a network of roads criss-crossing most of northern Botswana, previously surveyed by former wildlife biologist with the Department of Wildlife and National Parks Botswana, Dr Marc Herremans. The team retraced Herremans’ route across gravel and tar roads in a similar vehicle and at similar traveling speed. They spotted birds with the naked eye, only using binoculars to positively identify bird species, as per the original survey. The survey focused on 29 raptor species and compared their encounter rate with Herremans’ original records.
The motivation for doing the work was to explore whether vulture and raptor numbers had declined in Botswana, as they have in many other areas of Africa. Sadly, species declines were detected for 14 of the 29 species monitored, with 11 of these species declining by over 50% in the last 20 years. Some of the species showing the greatest declines are the white-headed and lappet-faced vultures, African hawk eagle, secretary bird, bateleur and red-necked falcon. Only three species, the brown and black-chested snake-eagles and the tawny eagle, were more abundant. Although declines in raptor populations have been seen elsewhere in Africa, particularly across West Africa, researchers were not expecting such dramatic declines in Botswana. The country has a relatively low human population size and nearly 40% of the land is under some form of protection.
The study did not pinpoint the cause of the declines, but conservationists say vultures in particular are vulnerable to poisoning by poachers for whom the birds’ habit of circling carrion is a threat, as it might draw attention of game rangers inside protected areas. Another recent study found a third of all vultures caught and tested in a separate Botswana study showed elevated levels of lead in their blood, most likely due to ingesting bullet-contaminated flesh.
The road-trip study also found significant declines of many species inside protected areas, which suggests the main factors driving species declines transcend habit conservation status. Furthermore, drivers of decline are apparently indiscriminate, inexplicit and are likely acting jointly, making defining appropriate conservation measures challenging.
The study findings also highlight the importance of historical data in countries where scarce funding resources result in limited species monitoring. The sharp declines found in the latest survey would not have been observed without reference to Herremans’ original survey, which covered a much wider area of about 50 000km of road. As the repeat study concentrated only on the northern transects, researchers would now like to repeat the remaining routes in the south of the country to explore whether the trends in the north represent the overall trends for the country.
Written by Beckie Garbett and Arjun Amar, FitzPatrick Institute of African Ornithology at the University of Cape Town
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