- The Philippine eagle has been declared threatened with extinction for nearly three decades, but little is definitely known about its range and its wild population.
- Using satellite images, decades of georeferenced nest locations, and data from citizen scientists, a team of researchers identified 2.86 million hectares (7.07 million acres) of forest suitable for the eagles, which they estimate host around 392 breeding pairs.
- Only 32% of the identified habitats fall within the Philippines’ current protected area network, prompting researchers to call for stronger protection measures for the endemic raptor.
The Philippine eagle, the archipelagic nation’s iconic, endemic apex predator, has been declared threatened with extinction for nearly three decades. Yet despite its status as the national bird, little is definitively known about the extent of the raptor’s range and its numbers in the wild.
A recent study published in the journal Animal Conservation is trying to change that, raising hope among conservationists who are racing against time to save this keystone, and critically endangered, species.
Scientists from nonprofits The Peregrine Fund (TPF) and the Philippine Eagle Foundation (PEF) identified a total of 2.86 million hectares (7.07 million acres) of forest habitat suitable for the Philippine eagle (Pithecophaga jefferyi), which they estimate host around 392 breeding pairs. This new global population estimate is higher than previous estimates of 340 pairs in 2018 and 88-221 pairs in 1989.
“The new study renewed our hope that we can improve the conditions of our imperiled national symbol within our lifetime,” paper co-author and PEF research and conservation director Jayson Ibañez told Mongabay in an instant message.
Using satellite images, decades of georeferenced nest locations, and data from citizen scientists, the researchers modeled the eagle’s area of habitat and preferred land cover type, which appears to be dense, multilayered forest canopies. The population estimate was calculated using home range size requirements observed in breeding adults fitted with satellite tracking tags.
The researchers say the findings can help improve the effectiveness of eagle conservation decision-making and actions. “Establishing baseline estimates for both of these parameters [species distribution and population size] is critical for directing conservation planning for at-risk endemic species like the Philippine eagle,” Luke Sutton, lead author and post-doctoral research fellow at TPF, said in a statement.
The study predicted that the available habitat on the southern island of Mindanao (at 1.7 million hectares, or 4.2 million acres) could potentially support 233 breeding pairs (within the range of 190-266); the largest island of Luzon, with 935,000 hectares (2.3 million acres) of suitable habitat was predicted to be able to support 128 pairs (range: 104-146); and the Eastern Visayas cluster of islands, with 224,000 hectares (553,000 acres) of habitat, potentially 31 pairs (range: 25-35).
“It represents a substantial improvement in our knowledge of the distribution of these birds, but it is essential that this is now followed up with ground-truthing surveys to confirm or refute their findings,” Alex Berryman, Asia and Pacific red list officer at the nonprofit BirdLife International, told Mongabay via email.
While Berryman, who was not part of the study, said this represents the “first robust attempt to estimate [Philippine eagle] population size using the area of available suitable habitat,” he notes there are some limitations to the methodology.
“Because they applied a population density (territory size) derived from Mindanao, the population sizes they calculated for other islands may not be accurate. For example, it has long been hypothesized that Philippine eagles occur at lower densities on Luzon because of the absence of colugo and other arboreal mammals [that the eagles prey on], so I suspect their calculated estimate for Luzon may be optimistic,” he said.
Within these major islands, the paper specifically identified several mountain ranges as priority conservation areas, narrowing conservationists’ search for the remaining eagle families.
“The goal now is to find as many of those 392 eagle pairs and their nesting sites, and provide protection, particularly [for] those that are vulnerable to human-eagle conflicts,” Ibañez said.
Berryman said the model provides a good starting point of areas to search and survey occupancy or density, especially for inadequately surveyed islands such as Samar and Leyte in the Eastern Visayas.
Threats
The study noted that the current Philippine protected area network covers only 32% of the suitable eagle habitats. Falling outside the network makes the eagles’ nesting territories more vulnerable to deforestation.
Ibañez called on the Philippine Department of Environment and Natural Resources to clearly identify and designate these nesting sites as either strict protection zones or habitat management zones to make their conservation non-negotiable.
For areas under the management of local governments, Ibañez said local forest and land-use plans must be revisited. “Eagle nest sites are commonly found in lowland or upper dipterocarp forests, but these forests are normally within multiple-use zones or areas allotted for human uses. Zoning reclassification must be undertaken in these cases,” he said.
The researchers also say there need to be an increase in funding for local environment offices’ wildlife and forest law enforcement efforts. They say local bans on airguns, improvised firearms and illegal firearms will help address the shooting and hunting of eagles, especially the most vulnerable juveniles, a problem that is seriously hurting wild populations. This problem is particularly egregious in Mindanao, where more than 200 of the 392 pairs estimated breeding pairs are thought to be found.
“We can lose these eagles even if good forests are present if the hunting pressures are high,” Ibañez said. “Such cases of ’empty forests’ — forests empty of its apex predators and large animals because of excessive hunting — we believe are already happening.”
Berryman agreed, saying, “With hunting as a threat especially on Mindanao, it is possible that areas of suitable habitat that should be occupied are not.”
Reintroduction
Immature, unpaired “surplus” eagles that are at risk of getting shot and killed in Mindanao, Ibañez said, can be reintroduced to vacant forest habitats that the study has identified as highly suitable. These include mountains in Leyte and central and southern Luzon that might have lost their eagles but are still of high quality.
“If we capture these birds and translocate or transfer them to vacant suitable habitats that are already protected in Leyte and Luzon, then we can increase the survival chances and reproductive potential of these birds,” he said.
The researchers say they hope their paper will guide concerted actions to pull this ecological keystone species from the brink of extinction. “We, particularly the government, have no reason or alibi to dilly dally because the roadmap is clear,” Ibañez said.
Banner image: A Philippine eagle with its solar powered GPS tracker harnessed on its back in the Mt. Apo region. Image by Philippine Eagle Foundation.
A good year for the Philippine eagle in 2020, but not for its supporters
Citation:
Sutton, L. J., Ibañez, J. C., Salvador, D. I., Taraya, R. L., Opiso, G. S., Senarillos, T. L. P., & McClure, C. J. W. (2023). Priority conservation areas and a global population estimate for the critically endangered Philippine Eagle. Animal Conservation. doi:10.1111/acv.12854
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