THE Philippine Eagle Foundation (PEF) endeavors to find all eagle nesting sites within the Mt. Apo Key Biodiversity Area (KBA) and help protect each of these nest sites.
Philippine eagle nest sites are ancient breeding areas – generations of eagle pairs have occupied the same nest site over and over again. Conserving these core areas of reproduction and keeping the nesting pair and their young safe is pivotal to the success of saving the species from being lost forever.
In 2019, the PEF, Energy Development Corporation (EDC), and the Department of Environment and Natural Resources (DENR) launched the “Search for the King of Birds” project at the western slopes of Mt Apo.
The search began at the Mt. Apo Geothermal Reservation in Kidapawan City where eagles were seen in the past. Apart from enhancing local awareness and capacity for eagle conservation, project implementers also wanted to find and study an eagle pair and their active nest at the reservation.
Two expeditions in 2019, one in July and another in September, found one Philippine eagle. The bird is suspected to be immature, perhaps over 3 years old, and thus is a floater (sexually immature and unpaired eagle). The presence of an immature eagle indicates that its eagle parents could be nearby.
The PEF Team -- Senior Biologist Ron Taraya and Field Intern Keanu Sitjar -- together with EDC Forest Aides Climclim Lumayon and Renjie Sinding, embarked on the month-long expedition in November to check on a possible new nesting territory of the Philippine Eagle.
The group focused their eagle search on the forests where a lone Philippine eagle was detected in 2019. The terrain at the survey site was very steep, and the forest vegetation is lush. With binoculars and field telescopes, the team alternately manned four observation posts (OP): three on the ground (OP1-3) and one on an elevated platform (OP4). OP4 offered the closest view of the gorge and its forests.
After spending 192 observation hours deep in the forest finding and documenting Philippine eagles and other raptors, the team managed to detect one eagle pair and their two-year-old young.
Confirming a Philippine eagle couple
It was on November 4 when the team saw their first Philippine Eagle pair. The first eagle was found perched inside the canopy above the waterfalls. The bird then took off and flew in circles above the falls. As it was about to head towards the other hill, another eagle appeared and started “chasing” the other eagle. The team recalled that their hearts raced at the sight of the eagles doing their elegant aerial rituals.
The eagle couple then began what appears to be a courtship routine. The two eagles mutually presented their talons in mid-air called “talon presentation”. They also did several bouts of flying together in spirals or “mutual soaring”. Then they flew to different directions; one disappearing inside the deep gorge, while the other landed on an emergent tree. There, the eagle stayed on its perch cleaning its feathers with its beak called preening. It was also seen scratching, stretching, and moving its head. After performing these general maintenance behaviors, the eagle finally flew off and glided beyond the waterfalls until it disappeared behind the tree line.
In Mindanao, September to January is the nesting season for Philippine eagles, and courtship displays precede each egg-laying. Eagle pairs at several nests sites of Mindanao start their courtship rituals above their nesting area as early as July, but the routine can last even until the pair is already rearing a chick. These observations strongly suggest that the forest the team investigated is a new Philippine eagle nesting territory at the Mt. Apo KBA.
Documenting a juvenile Philippine Eagle
On November 5, while occupying OP 2, the team was eager to see “prey delivery” and/or “sprig delivery” behaviors that would lead them to a possible nest.
To the group’s great delight, two eagles were spotted. The eagles glided steadily on a level cruise, with one trailing the other. They emerged from the same spot where one of the eagles disappeared the day before. One eagle landed on a tree that is visible to the group, while the other rested on a concealed spot.
While observing the pair, the team then heard loud, crying calls from another eagle. The calls were typical of “food-begs” from a very hungry young eagle. Food-begging calls are mostly exhibited by juveniles whenever an attending parent is nearby. The hungrier the eaglet, the louder its calls get.
The team occupied the post early the following day in anticipation of another eagle encounter. It was early in the morning when loud eagle calls were heard once again. The “food-begs” echoed across the forests and it took the team a while to find the eagle. Finally, the eagle emerged out of a tree directly above the waterfalls.
The bird was over a kilometer from the research team’s post, and at that distance, it was very difficult to see the bird’s physical features in detail. One can tell whether a bird is a juvenile or adult based on the shape of its feathers, the color of its legs, and its general appearance. The bird calls resemble infantile vocals, but the team needed to have a closer look to be sure. An adult delivering food and feeding the eagle is another proof that the bird is a juvenile.
While observing the eagle, an adult eagle appeared above the ravine and flew towards the direction of the calling bird. The adult eagle was seen to be carrying a freshly killed prey. The “food begs” intensified as the other eagle flew above the ravine. Minutes later another eagle soared above the feeding tree and disappeared behind the hills.
The team returned on November 7 to check whether the tree where the adult eagle dropped the food is a nesting tree. From afar, the feeding branch looked like a huge nest bowl. The researchers also wanted to know if the juvenile slept at that tree.
Later, they discovered that the eaglet indeed slept there. The team saw the eaglet was sun-bathing, drying its feathers using under the early morning sun.
During this visit, the team also encountered the eagle-parent. It landed on a different tree and left eventually. It flew above the tree where the young eagle was perched. It then disappeared behind the tree line. The juvenile eagle trailed its parent’s flight path and also disappeared behind the forests. The eagles were not seen for several days after this encounter.
To know for certain if the tree is a nesting tree, the team decided to find a closer observation post at the forest edge on November 12.
Upon closer inspection of the tree, it showed that it does not qualify as a suitable nesting tree. It did not have the typical nest bowl structure, the associated thick ferns, and other epiphytes that one will find in an old nest. It appears that the tree is more of a “feeding tree” than a nesting tree.
On November 13, the established OP4 – an elevated platform that gave them a good view of the whole forest. The following day, they occupied our new platform and waited.
It was in the afternoon when two Philippine eagles were again spotted circling just above the ridge. But the mutual soaring did not last a minute. Only one Philippine eagle landed on a spot that is visible to the team. The other eagle, which they suspect is the juvenile, hid behind the foliage. They heard it calling but never saw it for the rest of the day.
The team had another encounter with the juvenile Philippine Eagle on November 19 after it soared just above OP 4. Now closer to the bird, about 200 to 300 meters, the relatively sword-tipped flight and tail feathers of the juvenile eagle were visible. The bird also had all the other features typical of a two-year-old juvenile such as awkward hunting moves, lower flight confidence, and limited flight duration.
The juvenile eagle was also observed to hunt when it took on a group of long-tailed macaques (Macaca fascicularis) foraging on an escarpment just in front of the waterfalls.
Researchers saw the bird leaping from the tree and darting towards the macaques. The macaques panicked and ran frantically in different directions to avoid the eagle. While it did attempt to corner a macaque, the juvenile eagle’s attempt to hunt was unsuccessful as the macaque it had its eye on was able to escape. The macaques were also observed to have rallied together to scare off the eagle.
After the month-long expedition to observe and track a family of Philippine eagles, the researchers can confirm that they have discovered a new nesting territory of the eagle. The juvenile eagle is already in its post-fledging stage. Based on the general appearance of the juvenile eagle, its behavior, and the behavior of its parents towards it, researchers estimate that the age of the young eagle to be around two years old. Following the eagle’s nesting cycle on Mindanao, the eagle pair could also be laying an egg soon.
Aside from detecting the critically endangered Philippine eagle, seven other raptors seen during the expedition. These raptors are the Philippine Serpent Eagle (Spilornis holospilus), Philippine Honey buzzard (Pernis steerei), Brahminy Kite (Haliastur indus), Philippine Falconet (Microhierax erythrogenys), Chinese sparrowhawk (Accipiter soloensis), the crested honey buzzard (Pernis ptilorhynchus), and the Peregrine falcon (Falco peregrinus). (PEF)
***
Ron Taraya and Jayson Ibanez. Ron and Jayson are Biologist and Director for Research and Conservation, respectively, at the Philippine Eagle Foundation.