But securing prey has become increasingly difficult for one of the world’s largest raptors: Continued deforestation due to logging and development in the Philippines has pushed the eagle to the brink of extinction. Today those that remain struggle to find enough food and habitat to survive. Though some of these resourceful birds have adjusted to the reduced surroundings, development continues to threaten their existence. Conservationists are dedicated to providing the national bird a secure home. The Philippine Eagle Foundation on Mindanao hopes to save the species from extinction through its conservation and education efforts. Officially established in 1987, the center’s captive-breeding program has raised 21 birds over the past two decades.
Distribution and Habitat Edit
The Philippine eagle is endemic to the Philippines and can be found on four major islands: eastern Luzon, Samar, Leyte, and Mindanao. The largest number of eagles reside on Mindanao, with between 82 and 233 breeding pairs. Only six pairs are found on Samar, two on Leyte, and a few on Luzon. It can be found in Northern Sierra Madre National Park on Luzon and Mount Apo, Mount Malindang and Mount Kitanglad National Parks on Mindanao. This eagle is found in dipterocarp and mid-montane forests, particularly in steep areas. Its elevation ranges from the lowlands to mountains of over 1,800 metres (5,900 ft). Only an estimated 9,220 km2 (2,280,000 acres) of old-growth forest remain in the bird's range. However, its total estimated range is about 146,000 km2 (56,000 sq mi).
Ecology and Behavior Edit
Evolution in the Philippine islands, without other predators, made the eagles the dominant hunter in the Philippine forests. Each breeding pair requires a large home range to successfully raise a chick, thus the species is extremely vulnerable to deforestation. Earlier, the territory has been estimated at about 100 km2 (39 sq mi), but a study on Mindanao Island found the nearest distance between breeding pairs to be about 13 km (8.1 mi) on average, resulting in a circular plot of 133 km2 (51 sq mi). The species' flight is fast and agile, resembling the smaller hawks more than similar large birds of prey.
Juveniles in play behavior have been observed gripping knotholes in trees with their talons and, using their tails and wings for balance, inserting their heads into tree cavities. Additionally, they have been known to attack inanimate objects for practice, as well as attempt to hang upside down to work on their balance. As the parents are not nearby when this occurs, they apparently do not play a role in teaching the juvenile to hunt. Life expectancy for a wild eagle is estimated to be from 30 to 60 years. A captive Philippine eagle lived for 41 years in Rome Zoo, and it was already adult when it arrived at the zoo. However, wild birds on average are believed to live shorter lives than captive birds.
The Philippine eagle was known initially as the Philippine monkey-eating eagle because it was believed to feed on monkeys (the only monkey native to the Philippines is the Philippine long-tailed macaque) almost exclusively; this has proven to be inaccurate. This may be because the first examined specimen was found to have undigested pieces of a monkey in its stomach. Like most predators, the Philippine eagle is an opportunist that takes prey based on its local level of abundance and ease. It is the apex predator in its range.
Prey specimens found at the eagle's nest have ranged in size from a small bat weighing 10 g (0.35 oz) to a Philippinedeer weighing 14 kg (31 lb). The primary prey varies from island to island depending on species availability, particularly in Luzon and Mindanao, because the islands are in different faunal regions. For example, the tree squirrel-sized Philippine flying lemurs, the preferred prey in Mindanao, are absent in Luzon. The primary prey for the eagles seen in Luzon are monkeys, birds, flying foxes, giant cloud-rats Phloeomys pallidus which can weigh twice as much as flying lemurs at 2 to 2.5 kg (4.4 to 5.5 lb), and reptiles such as large snakes and lizards. The flying lemur could make up an estimated 90% of the raptor's diet in some locations. While the eagles generally seem to prefer flying lemurs where available, most other animals found in the Philippines, short of adult ungulates and humans, may be taken as prey. This can include Asian palm civets (12% of the diet in Mindanao), macaques, flying squirrels, tree squirrels, fruit bats, rats, birds (owls and hornbills), reptiles (snakes and monitor lizards), and even other birds of prey. They have been reported to capture young pigs and small dogs.
Philippine eagles primarily use two hunting techniques. One is still-hunting, in which it watches for prey activity while sitting almost motionlessly on a branch near the canopy. The other is perch-hunting, which entails periodically gliding from one perch to another. While perch-hunting, they often work their way gradually down from the canopy on down the branches and, if not successful in find prey in their initial foray, will fly or circle back up to the top of the trees to work them again. Eagles in Mindanao often find success using the latter method while hunting flying lemurs, since they are nocturnal animals which try to use camouflage to protect them by day. Eagle pairs sometimes hunt troops of monkeys cooperatively, with one bird perching nearby to distract the primates, allowing the other to swoop in from behind, hopefully unnoticed, for the kill. Since the native macaque is often around the same size as the eagle itself, at approximately 9 kg (20 lb) in adult males, it is a potentially hazardous prey, and an eagle has been reported to suffer a broken leg after it struggled and fell along with a large male monkey.
The complete breeding cycle of the Philippine eagle lasts two years. The female matures sexually at five years of age and the male at seven. Like most eagles, the Philippine eagle is monogamous. Once paired, a couple remains together for the rest of their lives. If one dies, the remaining eagle often searches for a new mate to replace the one lost. The beginning of courtship is signaled by nest-building, and the eagle remaining near its nest. Aerial displays also play a major role in the courtship. These displays include paired soaring over a nesting territory, the male chasing the female in a diagonal dive, and mutual talon presentation, where the male presents his talons to the female's back and she flips over in midair to present her own talons. Advertisement displays coupled with loud calling have also been reported. The willingness of an eagle to breed is displayed by the eagle bringing nesting materials to the bird's nest. Copulation follows and occurs repeatedly both on the nest and on nearby perches. The earliest courtship has been reported in July.
Breeding season is in July; birds on different islands, most notably Mindanao and Luzon, begin breeding at different ends of this range. The amount of rainfall and population of prey may also affect the breeding season. The nest is normally built on an emergent dipterocarp, or any tall tree with an open crown, in primary or disturbed forest. The nests are lined with green leaves, and can be around 1.5 m (4.9 ft) across. The nesting location is around 30 m (98 ft) or even more above the ground. As in many other large raptors, the eagle's nest resembles a huge platform made of sticks. The eagle frequently reuses the same nesting site for several different chicks. Eight to 10 days before the egg is ready to be laid, the female is afflicted with a condition known as egg lethargy. In this experience, the female does not eat, drinks lots of water, and holds her wings droopingly. The female typically lays one egg in the late afternoon or at dusk, although occasionally two have been reported. If an egg fails to hatch or the chick dies early, the parents will likely lay another egg the following year. Copulation may take place a few days after the egg is laid to enable another egg to be laid should the first one fail. The egg is incubated for 58 to 68 days (typically 62 days) after being laid. Both sexes participate in the incubation, but the female does the majority of incubating during the day and all of it at night.
Both sexes help feed the newly hatched eaglet. Additionally, the parents have been observed taking turns shielding the eaglet from the sun and rain until it is seven weeks old. The young eaglet fledges after four or five months. The earliest an eagle has been observed making a kill is 304 days after hatching. Both parents take care of the eaglet for a total of 20 months and, unless the previous nesting attempt had failed, the eagles can breed only in alternate years. The Philippine eagle rivals two other large tropical eagles, namely the crowned eagle and harpy eagle, for having the longest breeding cycle of any bird of prey. Even nests have no predators other than humans, as even known nest predators such as palm civets and macaques (being prey species) are likely to actively avoid any area with regular eagle activity.
Philippine Eagle Courtship and Reproduction Edit
Female eagles reach sexual maturity at five years; males, at seven. Courtship behavior includes soaring together in the air, diving and chasing each other, exposing talons, and increased vocalization. Nest building—often in dipterocarp trees, which can be 80 to 160 feet off the ground—and an increase in the amount of time spent at the nest also indicate a willingness to breed. Like other eagles, this species is thought to stay monogamous until one of the pair dies.
A breeding pair typically produces a single young every other year. In Mindanao egg-laying season starts in September and may go until February; in Luzon, it goes only from December to January, shortened perhaps because the peak typhoon season, from September to November, is not conducive to egg laying. Both the male and female incubate the egg, though the female tends to spend more daytime hours and all night in the nest. Once hatched, the eaglet stays in the nest for about five months, dependant on its parents for food. After that, it remains in its parents’ home range and partly in their care for another 12 months or so.
Though most immature birds die before reaching sexual maturity, the species has the potential for a long life span. A Philippine eagle living in a zoo in Rome, Italy, may have been up to 41 years old when it died, although the eagle’s life span in the wild is thought to be shorter.