Raptors on the Brink: Population Declines Over Africa’s Savannas

Featured Image Caption: The secretary bird (Sagittarius serpentarius), one of Africa’s most unique raptors, is currently listed as Endangered by the IUCN. This study suggests that its threat status should be increased. Photo by Bernard Dupont, CC BY-SA 2.0

Source Article: Shaw, P., Ogada, D., Dunn, L. et al. African savanna raptors show evidence of widespread population collapse and a growing dependence on protected areas. Nat Ecol Evol (2024). https://doi.org/10.1038/s41559-023-02236-0 

Africa’s rapidly growing population is converting ever more land to agriculture, a shift which has serious consequences for the continent’s rich biodiversity. Among the groups threatened are the diurnal raptors: vultures, eagles, hawks, falcons and the endemic secretary bird. Raptors also suffer from hunting and trapping, poisoning, collisions with energy infrastructure, and prey population collapse. 

Survey routes in the four study areas covered in the study. Protected areas highlighted. Surveys were conducted 1969-1977 and 2000-2020 in northern Cameroon, Kenya, and West Africa, and 1995-1999 and 2015-2016 in Botswana. Image from Open Access article Shaw et al. 2024. 

Declines among diurnal raptors are particularly concerning as many of them are top predators, meaning that their population crashes trigger cascading effects throughout food chains: with fewer top predators around, prey species (smaller birds and mammals, for instance) explode in population, putting pressure on their own prey (insects). This process can have unpredictable consequences for both humans and ecosystems. Additionally, many species – particularly vultures – provide the crucial service of carcass disposal, which lessens the threat of zoonotic disease spread – a threat that is only too clear in our post-COVID world. 

Despite the importance of diurnal raptors, there is limited long-term data on their populations throughout Africa. Researchers filled that gap by analyzing the results of surveys conducted from 1969-1995 and 2000-2020. During the earlier period researchers conducted surveys along defined routes and recorded how many diurnal raptors were found. They then repeated these survey routes during the later period, using the change in encounter rate over time as a proxy for population trend. Surveys were conducted in savannas across four regions of the continent: West Africa (Burkina Faso, Niger, Mali), Central Africa (northern Cameroon), East Africa (Kenya) and Southern Africa (Botswana). Researchers assessed population trends for 42 species, along with the difference in trends between protected and non-protected areas. 

THE BIGGER THEY ARE, THE HARDER THEY FALL 
The relationship between body mass and population declines among African raptors. Image from Open Access article Shaw et al. 2023.

The results were not reassuring: populations of 37 out of 42 species were found to be declining, with 29 of them declining by at least 30% over three generations. The International Union for Conservation of Nature (IUCN) uses this criterion to classify species according to extinction risk; these classifications are then used by NGOS and governments to determine conservation priorities. A 30% decline corresponds to a status of Vulnerable, meaning a species is at a high risk of going extinct in the wild. Several of these rapidly declining species are currently classified by the IUCN as Least Concern, suggesting that a re-classification may be in order. A further 6 species already classified as globally threatened were found to suffer declines warranting an increase in their threat status. 

Larger species suffered significantly sharper declines than their smaller relatives. Not only were annual declines higher in larger species, but this difference was compounded by the larger raptors’ longer generation lengths: alarmingly, the 10 largest species were all found to decline by 60% over three generations. This relationship between individual size and population decline is also found in mammalian predators. In general, large predators require extensive home ranges and exhibit low population density, low birth rates, and delayed sexual maturity, all of which predisposes them to extinction risk. 

The region with the greatest declines was West Africa, with species declining there over twice as fast as the other regions. This is not surprising given the region’s social realities: it is experiencing the fastest population growth, the fastest transition to agriculture, the highest levels of poverty and persistent armed conflict. Previous research has shown that corruption within West African parks has had adverse consequences for lions and elephants; the same is likely true for raptors as well. 


PROTECTED AREAS OFFER A GLIMMER OF HOPE 
The lappet-faced vulture (Torgos tracheliotos) is the largest vulture across its range. Currently classified as Endangered, the study lists it as one of six imperilled species whose threat level should be further increased. Photo by Dominic Sherony, CC BY-SA 2.0. 

Protected areas provided a critical buffer against population decline. Across the continent, annual declines within protected areas were less than half those of unprotected areas, with the most pronounced contrast in East and West Africa. While larger species declined faster than small species in both protected and unprotected areas, the difference was more muted within protected areas, meaning that these were especially important for larger species. Protected areas were also crucial for rapidly declining species irrespective of their body size. Despite the crucial role they play, however, 17 of the 42 species declined within PAs at a rate corresponding to an IUCN status of Vulnerable, Endangered, or Critically Endangered. Indispensable as they are, protected areas are not immune from the general collapse of raptor populations across the continent. 

How can Africa’s raptors be brought back from the brink? PAs will clearly play a crucial role: currently 19% of the continent’s surface area is protected, whereas the Convention on Biological Diversity COP15 specifies a target of 30% by 2030. Meeting this challenge, along with improving PA management and connectivity, would support all of Africa’s wildlife, raptors included. The replacement of chemical pesticides with bio-pesticides would benefit many species, as would the protection of nesting sites like cliffs. Law enforcement combined with economic incentives could lessen the persecution of certain species. Infrastructure like power lines and wind turbines – both of which will, hopefully, expand dramatically in the coming years – should be designed to minimize avian fatalities.  

The decline of African savanna raptors is part of a global trend: raptors throughout the world are suffering sharper declines than birds as a whole. The success of several high-profile recovery efforts (peregrine falcons, Mauritius kestrels and California condors, to name a few) show that conservation efforts can make the difference between extinction and survival. In any scenario, however, the continent’s raptors have a tough road ahead, with their fates linked to the state of Africa’s ecosystems and the socioeconomic needs of its human population. 

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PJ Donworth

I am an MSc candidate in Organismic Biology at the University of Bonn currently researching the diversity of wild bees in the city of Bonn. I'm interested in writing about insects, conservation, urban ecology, and climate change. I also enjoy include reading and writing, political engagement, hiking, and yoga.

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