Philippine Eagle Biology and Ecology

B. Feeding Ecology

The food habits of the Philippine Eagle are known from prey items brought into nests. Studies from 1978 to 1983 revealed that 15 species of vertebrate prey were used for feeding the young including flying lemurs, squirrels, snakes, civets, hornbill, bats and monkeys. But of these prey species, eagles seem to prefer flying lemurs and civets. For the past three decades, only three studies were done on Philippine Eagle breeding and food habits and contrary to persistent claims, no domestic animals were ever brought to nests. The table below shows the list of prey species identified during a study by Kennedy (1985). This table was modified from Kennedy.

The variety and size differences of prey suggest that the Philippine Eagle is an opportunistic hunter with preference for tree-dwelling species. Investigators also suspect that eagles are capable of shifting prey, choice of prey may also coincide with the breeding season of the particular prey.

Observations of their hunting behavior are scant. But more recent detailed observation provided starling revelations. The juvenile learns hunting behavior without parental intervention. Philippine Eagles hunt from perch, constantly observing knotholes or cavities in trees. Adults have been observed to poke their talons into tree cavities to apparently grab prey. One investigator believed that the relatively longer tarsus of the Philippine Eagles is an adaptation to taking prey from tree cavities. But this hypothesis needs further testing.

Meanwhile, the food habits of Philippine Eagles in Luzon have not yet been documented. Because of the difference in terms of the faunal composition of Luzon and Mindanao, them representing different faunal regions, the eagles there would definitely have a different diet regime. For example, flying lemurs, which are the preferred prey in Mindanao, is absent in Luzon. A food habit study in Luzon is long overdue.

C. Regional Breeding Density and Population Estimates

The current population status of the Philippine Eagle is not known. The species has been considered rare since it was discovered in 1896. Moreover, the eagle has always been difficult to census because of the significant logistic difficulties of working in dense, steep rainforest.

Previous attempts to survey or estimate the population status of the species have always been crude at best. Only scattered, individual reports occurred up through the 1960’s. Additionally, data from researchers in the 70’s to the early 80’s were difficult to interpret. And because of the small sample sizes and nature of approaches used, no confidence limits could be established for these estimates. However, based on systematic surveys in the last decade, breeding density estimates suggest there are about 200 pairs in Mindanao. Using the same estimates, about 300 pairs could be present in the other islands where it has been found.

The general indicators of population status continue to be alarming. Habitat and probably prey populations are continuing to disappear at a rapid rate. Thus, wild populations are losing places to live and are likely becoming food-stressed. Hunting and shooting of wild birds also persist. Eagles that were turned over to the Philippine Eagle Center in recent years either had gunshot wounds or were trapped illegally in the wild. Even birds that seemed healthy at the time of recovery or confiscation were found to have airgun pellets in their bodies after undergoing X-ray examinations.

Of the two primary characteristics of populations, i.e. reproductive rate and survival rate, the latter is the most important for populations of long-lived, slowly reproducing species such as the Philippine Eagle. Chance effects (such as weather fluctuations, epidemics, inbreeding, etc.) only make matters worse for small populations.