Survey reveals decline in birds of prey species

A TWO-YEAR project to repeat a famous bird survey by driving over 20 000km across Botswana has confirmed researchers’ fears – that many birds of prey are fast disappearing from one of Africa’s last great wilderness areas.

Reported sightings of iconic species of eagle and vulture declined by as much as 80% compared with the previous survey, while some migrant species recorded last time have vanished, according to the study published last week in the international scientific journal Biological Conservation.

The recent study was conducted by researchers at the FitzPatrick Institute of African Ornithology at UCT in collaboration with conservation non-governmental organisation Raptors Botswana.

Their data is based on a return trip to a network of roads criss-crossing most of northern Botswana, an area first surveyed over 20 years ago by Dr Marc Herremans, a former wildlife biologist with the Department of Wildlife and National Parks Botswana.

Researchers retraced Herremans’ route. The resurvey focused on 29 raptor species and compared their encounter rate with Herremans’ original records.

“Main motivation for the work was to explore whether vultures and other raptor numbers had declined in Botswana like in many other areas of Africa,” said Associate Professor Arjun Amar from the FitzPatrick Institute.

“Although declines in raptor populations have been seen elsewhere in Africa, particularly across West Africa, we were not expecting these declines to be quite so dramatic in Botswana, which has a relatively low human population size and where nearly 40% of the land is under some form of protection,” he said.

Species declines were detected for 14 out of 29 species monitored. Eleven of these species declined by over half 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 eagle, and red-necked falcon. Only three species showed an increase in their abundance: the brown and black-chested snake-eagle and the tawny eagle.

The study does not point to the cause of the declines. However, conservationists say vultures are vulnerable to poisoning by poachers, for whom the birds’ habit of circling carrion is a threat because it might draw attention of game rangers inside protected areas.

PhD student Beckie Garbett, who led the latest road transect study, said: “We found declines occurring across species with varying diet and habitat use, which make it hard to pinpoint the main drivers of decline. Climate change is one candidate for these declines, but urgent research is needed to better understand the drivers of these declines.”

The road trip study also found significant declines of species inside protected areas.

The study findings highlight too the importance of historical data in countries where scarce funding resources result in limited monitoring.

The sharp declines contained in the latest survey would not have been observed without reference to Herremans’ original survey, which actually covered a much wider area – about 50 000km of road. Herremans said he was pleased that his data had proved valuable “and that they contribute to our knowledge of long-term changes in bird populations”.

“It is sad, though, to learn that even in this country with so much of the land devoted to conservation, biodiversity is in steep decline,” Herremans said.