Birds of prey are declining all throughout the world, according to new research, putting the health of ecosystems at risk. Habitat destruction is the main driver of this decline.

The paper analyzed data from the International Union for the Conservation of Nature (IUCN) and BirdLife International, a global partnership of non-governmental organizations involved in the conservation of birds and their habitat. Overall, the data showed that around 50% of the 577 bird of prey (raptor) species worldwide are declining in number. Roughly 30% are threatened, vulnerable, endangered, or critically endangered, with 18 species falling into the latter category.

Several species are also at risk of becoming locally extinct, even if they’re faring relatively okay as a whole species, the team explains. This means that they would no longer be able to act as top predators in certain ecosystems, a role critical for ecosystem health.

Bird issues

“The golden eagle is the national bird of Mexico, but we have very few golden eagles left in Mexico,” said Gerardo Ceballos, a bird scientist at the National Autonomous University of Mexico and co-author of the study.

The main threat to these birds is habitat destruction, the team explains, both through the direct issues it creates for them, such as a lack of adequate nesting areas, increased in-species competition for space and resources, as well as through indirect effects, including lower populations of animals that serve as prey.

Over half of raptor birds that are most active during the day (54%), including most hawks, eagles, and vultures, are showing ongoing population declines. Nocturnal raptors are faring somewhat better, with only 47% of species in this category showing population decline. This showcases that birds are experiencing strong pressures right now, not past pressures that have affected their numbers but have been addressed in the meantime. In other words, affected species will only fare worse over time, and it’s possible that new ones will also start being affected unless action is taken.

Apart from habitat destruction, other leading causes for the decline of raptors highlighted in the study include compounds such as rodent poison, used in agriculture, and lead shot that is typically used for hunting birds. Raptors routinely feed on rodents and carrion, so these compounds inadvertently affect them. Heavy use of anti-inflammatory drugs in livestock is also propelling the rapid decline of raptors, through the same mechanism. This is an issue particularly in South Asia, where some species have declined by 95% in recent decades due to the consumption of livestock carcasses.

The paper lists 4,200 sites previously identified by conservation groups as being essential for the health of raptors globally. According to the team, most of these are not protected in any way, or only enjoy partial coverage by protected areas. To illustrate how this state of affairs can impact raptor communities over a wide geographical range, the authors give East Asia as an example. Raptor species here tend to breed in north China, Mongolia, or Russia, and then migrate down the eastern coast of China to spend summers in Southeast Asia or India.

Multiple species will thus travel through a handful of sites throughout their migrations, so issues in any one of them will have wide-ranging impacts. Eastern China, for example, is very densely populated and highly urbanized, so sites in this area are facing massive pressures from human activity, including habitat destruction and contamination with agricultural compounds.

The paper “Global patterns of raptor distribution and protected areas optimal selection to reduce the extinction crises” has been published in the journal PNAS.