Low genetic diversity puts Philippine eagle at risk of disease, breeding issues - study

The Philippine eagle has been identified as vulnerable to various threats as modern deforestation has intensified its decline, based on findings from a recent genome study.

Researchers who analyzed the genomes of 35 Philippine eagles said the species’ population may have already been declining for around 3,000 years, leaving today’s remaining eagles more vulnerable to disease, environmental change, inbreeding, and continued habitat loss.

The study, published in the journal BMC Genomics in April, examined blood samples from 35 Philippine eagles under the care of the Philippine Eagle Foundation.

Scientists found that the species has “extremely low genetic diversity,” including signs of two historical population crashes and a long-term decline.

“The species went through major population crashes in the past. More recently, its population appears to have been declining for around 3,000 years. This means today’s threats—forest loss, hunting, trapping, shooting, mining, and human disturbance—are now hitting a species that may have already been weakened over a very long time,” the Philippine Eagle Foundation (PEF) said in a feature accompanying the study.

Among the eagles studied were CJ, also known as Lipadas, who survived after being hit by a marble gun that cost him his right eye, and Gavra Maslog, an eagle rescued after being trapped and mutilated, with portions of her talons reportedly cut off due to superstition-linked practices.

The study found that both eagles had some of the lowest measured heterozygosity levels among the sampled birds—meaning they carried very low genetic variety even within an already endangered population.

“Heterozygosity means genetic variety. A population with more genetic variety has more chances to adjust to disease, environmental change, and future breeding problems,” the PEF explained.

Researchers said low genetic diversity reduces the species’ ability to adapt and recover, especially as populations become smaller and more isolated.

“This study tells us that the Philippine eagle is not only rare in the wild; it is also genetically fragile,” said Cynthia Saloma, dean of the College of Science at the University of the Philippines Diliman and corresponding author of the study.

“Every eagle we lose may carry genetic variation that the species can no longer easily replace,” Saloma added.

The study estimated the average genome-wide heterozygosity of the sampled Philippine eagles at 0.000309, with some individuals reaching even lower values of 0.000207—figures researchers described as among the lowest reported among raptors with available genomic data.

Conservationists said the findings highlight the growing importance of science-guided conservation breeding programs alongside habitat protection.

Because Philippine eagles reproduce slowly, with females typically laying only one egg every two years in the wild, researchers said carefully managed breeding programs could help preserve remaining bloodlines and reduce risks associated with inbreeding.

The study noted that captive breeding programs can allow conservationists to pair unrelated eagles, protect rare genetic lines, and potentially increase breeding rates through techniques such as double clutching.

Still, researchers emphasized that breeding programs alone will not save the species without stronger forest protection and safer habitats.

“A genetically strong eagle still needs a safe forest,” said Dennis Salvador.

The Philippine eagle remains listed as critically endangered by the International Union for Conservation of Nature (IUCN), with habitat destruction and human activity continuing to threaten its already fragile population. — VBL, GMA News