Could ‘assisted migration’ help Ethiopian birds threatened with extinction?

Young white-tailed swallows in Ethiopia. Higher temperatures will likely affect their ability to breed. © Andrew Bladon

A swallow and a crow species are likely to go extinct in Ethiopia due to climate change and conservationists may be left with no option but to relocate some of them in a move known as "assisted migration", according to a new study.

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The authors of the study, published in the journal Plos One, say their climate change models show that up to 84 percent of the white-tailed swallow’s current range and 100 percent of that occupied by the Ethiopian bush-crow risk becoming unsuitable over the next 50 years. There is a high risk the birds will die out because it will be too hot to forage for food and breed.

Their long-term survival could depend on human intervention, or “assisted migration”: a process that would see some birds from each species captured, bred in captivity and then released in cooler areas elsewhere in Africa.

“It's probably our best chance of saving these two species,” Andrew Bladon, lead author of the study told RFI, although he stressed that such a conservation measure would be fraught with potential risks.

“The first hurdle would be finding a new location where we are pretty sure that the climate is suitable, the habitat is suitable, and there is enough space for a viable population,” he says.

Uncharted territory 

“Neither of these species have ever been translocated or kept in captivity, so we don't know how they would cope with being caught and moved to another location.”

Such drastic action might suit the bush-crow more. It has a varied diet and, being a crow, is highly adaptable.

Ethiopian bush-crows are a highly-adaptable species. © Andrew Bladon

But it would need to be carefully monitored in any new environment.

Bladon says the bush-crow has “all the traits of an excellent invasive species. So releasing bush-crows into an area with a more suitable climate could risk upsetting the ecosystem in the new location, threatening other species.”

Balancing act 

The high-flying, insect-eating swallow would likely prove even harder to move.

The University of Cambridge zoologist says the most likely place where the swallow could survive is somewhere in South Africa. But that country is already home to the closely-related pearl-breasted swallow. Introducing the Ethiopian swallow there could increase competition between them that could threaten both species.

“It's a really hard balancing act,” he says. “The alternative is to sit and watch these two charismatic species go extinct.”

Ethiopian white-tailed swallow chicks are raised in grass-lined nests made from mud. © Andrew Bladon

Ethiopia is home to diverse habitats -- deserts, grasslands, lakes, rivers, forests and mountain peaks -- and specialist species that may not cope with rapid changes brought by climate change, explains Bladon.

In the region where the swallow and the bush-crow live -- known as the Borana Zone -- there are another three bird species (a turaco, a lark and a francolin) found there and nowhere else.

Assisted migration of vulnerable birds and other animal species could well become a feature of conservation work in Africa and elsewhere in the face of climate change. In Hawaii, seabirds have been bred in captivity to establish new colonies and keep them safe from sea level rise. 

Bush-crows build their large stick nests on the top of acacia trees in Ethiopia, and white-tailed swallows build their mud-cup nests under the roofs of huts. © Andrew Bladon

No easy solution

“Translocations beyond the historic range will be an increasingly important conservation option, in Africa and globally,” says Sarah Skikne, a postdoctoral researcher at the University of Minnesota's Institute on the Environment, who was not part of the Ethiopian study.

“Climate change means that suitable climates are moving out from under species, and land conversion such as agriculture will block their ability to follow their climates by shifting ranges.” 

But Skikne, who co-authored a 2020 study analysing past global translocations of 176 bird species to work out its feasibility as a climate adaptation tool, told RFI she shared the conclusion ultimately reached by the authors of the Ethiopian study: that assisted migration for the white-tailed swallow and the Ethiopian bush-crow is probably unfeasible. 

“My work shows that translocating birds over longer distances tends to decrease survival, so looking further afield may be risky,” Skikne says.

“This is an unfortunate example where there is no straightforward solution.”