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Cynthia Galang's Monkey Eating Eagle Report
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The Disappearing Predator: The Monkey-Eating Eagle

What kind of animal would be so powerful that it can devour a monkey for lunch? What animal could binge on whole chicken, deer, pigs and other small mammals for a meal? One can probably imagine a five- hundred pound carnivore with saber-tooth fangs, a grisly face, long limbs with fingers that can tear monkey meat into small bite size pieces. Among the eight thousand species of birds, sixty different kinds of eagles, why is the Monkey-eating eagle special? The Philippine eagle, better known by its descriptive name the monkey-eating eagle is the largest eagle in existence. Known as "Haring Ibon" or "Bird King" the monkey-eating eagle, this magnificent creature is found only in isolated areas in the Philippines and is considered endangered having only less than four hundred known that are surviving. The monkey-eating eagle is a top predator, animals that devour other animals. Their role primarily in ecosystems is to control the number of smaller animals in existence. All animals, regardless of their classification, predator or prey have a role to keep the balance in the ecosystem. Top predators help control the overpopulation of smaller animals that can cause sickness like rats, snakes, bats, lizards and other smaller creatures.The endangerment of a certain species will signal an imbalance in the ecosystem. This discussion focuses on the monkey-eating eagle as an endangered creature. Its name, classification in the animal kingdom, habitat and range, a physical description, behavioral, structural and physiological adaptations, survival status and current research will also be discussed.

A fierce raptor, the Monkey-eating eagle is part of kingdom Animalia, phylum Chordata, class Aves, order Falconiformes, family Accipitridae with a subfamily of Circaetine, genusPithecophagus, and its species name is Pithecophagus jefferyi (Anonymous C 2009, 1; Bhawani 2011, 1; Siojo 2008, 1). It is related to the much smaller Snake Eagle. A contradiction to the previous belief that due to their size and strength, they must be closer related to the Harpy Eagle, Crested Eagle, and the New Guinea Harpy Eagle (Siojo 2008, 4).  In 1896, discovered by John Whitehead, a British explorer and scientist, he gave it the name "Pithecophagus jefferyi" (Ullrichver 2008, 10). The inspiration came from the Greek terms "pithecus" (ape or monkey) and "phagus" (eater of) (Siojo 2008, 3). The second half of the name, "jefferyi" was in homage of Whitehead's father, Jeffery, who financed his son's travels (Ullrichver 2008, 10).  

Figure 1.- Monkey-eating eagle (Diana 2011, 

This magnificently enormous bird lives in the rain-forest and can be found on only four islands in the Philippines: a few were sighted in eastern Luzon, a couple in Leyte, six pairs in Samar, and 82-233 pairs in Mindanao (Siojo 2008, 9; Reyes 2008, 7). A breeding pair needs 25-50 square miles of of territory to raise a chick and hunt for sufficient food sources. " 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 meters ( 5,905 feet). It is estimated that only 9,220 square kilometers (2,280,000 acres) of old growth forests remain in the bird's range. However, its total estimated range is about 146,000 square kilometers (56,000 square miles)" (Siojo 2008, 13; Anonymous A 2011, 3).

The back of the Monkey-eating Eagle is a rich, dark brown and its underside is white. It has large, powerful claws, and heavy, yellow legs. It has unique, blue-gray eyes and a large, bluish-gray beak. The Philippine Eagle has a dark face, creamy-brown nape, and a spiky, brown crest of feathers that it displays when it is alert. Its impressive crown has been likened to a lion's mane and to the mythical griffin. Their wings are about 6 feet long (2 meters), are quite broad, and have a greater surface area than any other eagle.The Philippine Eagle is the world's largest living raptor in terms of length. "The female is up to 112 centimeters ( 3.82 feet) long with an average of 102 centimeters (3.36 feet) long and weighs about 7 kilograms (15.5 pounds). The adult male is about 10-20% smaller and averages at about 91 centimeters (3 feet) and 5 kilograms (11 pounds)" (Siojo 2008, 5, 7; Sace 2011, 2, 3; Ullrichver 2008, 7, 8; Mogwai 2009, 5; Anonymous A 2011, 1).

The Monkey-eating eagle was named so because its diet seemed to consist of monkeys. However, it has been known to eat prey ranging in size from small bats to 30-pound deer found in the wild. Prey examples include the flying lemur, owls, horn bills, snakes, monitor lizards, flying squirrels, rats, and other birds of prey. They have even been known to devour the occasional pig, goat, or dog! However, because the different islands, such as Luzon and Mindanao have different fauna regions, primary prey varies for the Philippine Eagles (Siojo 2008, 12; Ullrichver 2008, 3; Mogwai 2009; 2). (The name Monkey-eating Eagle was later changed to Philippine Eagle.)

Figure 2.- Philippine Islands
(Anonymous D 2012, 1)

 The Philippine Eagle pair are monogamous and will remain together for the rest of their lives. If one of the pair dies, the surviving eagle will find a new eagle partner to mate and reproduce with (Reyes 2008, 2; Anonymous B 2012, 4). It takes female eagles five and male eagles seven years to become sexually mature and be able to mate and reproduce (Sace 2011, 5; Ullrichver 2008, 4).

When they begin courtship, behavior includes an increased aerial display involving soaring in the air, diving, chasing each other, exposing talons, and increasing vocalization. Part of the ritual also includes building a nest about 80 to 160 feet above the ground. Repeated mating in the nest and in nearby places are signs that courting is at its peak. Egg-laying season is normally from September to February. However, due to the typhoon season (which is not ideal for egg-laying), in Luzon it is from December to January. When egg-laying draws near, females tend to to be more sickly. It is not uncommon for them to not eat for as many as 10 days as they fix their nest and only drink water. Then the egg is laid, usually in the afternoon (A breeding pair can only produce one egg every other year.). While both the male and female incubate the egg, the female does most of the work. When the male is not incubating the egg, it will usually be found hunting for food. Incubation will typically take 58-68 days. Once it hatches, the eaglet stays in the nest for about five and half months. The parents will only take care of the eaglet for 17 months until it leaves to look for a territory of its own. However, if the egg does not hatch, or the eaglet dies early, then the pair will produce another egg the following year. (Reyes 2008, 2, 3, 4; Ullrichver 2008, 4, 5; Cruz 2009, 3).

After 7-10 days of life, the eaglet is able to hold its head up. Then when 25-27 days has passed, it is able to stand momentarily. It starts flapping its wings after 32 days. The first pin feathers appear in scapulars after 37 days. Then it begins to walk after 45 days. After being alive for 54 days, it is able to eat by itself. 118-151 days is usually its first time out of the nest. The eaglet's first time out of the nest tree, or fledging, is 130-164 days after. Wandering from the nest area begins after 246-288 days. Then its first kill occurs after 304 days. Then the time for the eaglet comes to leave his parent's home and territory to begin a life of its own after 640 days (Reyes 2008, 5). Their life expectancy is estimated to be around 30-60 years with wild eagles having a shorter average life span than captive eagles (Reyes 2008, 1; Ullrichver 2008, 6; Siojo 2008, 14). 


(Nigge 2012, 1)


(Anonymous F 2009, 1).

Juveniles learn how to hunt not by their parents, but through their play. They have been observed gripping knotholes in trees with their talons. Then by using their powerful tails and wings for balance, will stick their heads inside holes in the trees. Also, they will try to hang upside down to work on their balance. They even attack inanimate objects to practice their skills (Siojo 2008, 11).

The bird's impressive call is a loud, high-pitched whistle. Juveniles often whistle when they want to signal that they want food. They display their "mane" of feathers when they are alert. An eagle will twist its head around to change how it sees things and to determine an object's size and distance. This helps it know if there is prey or some type of danger nearby (Ullrichver 2008, 7; Mogwai 2009, 5). 

 (Anonymous E 2011, 1)

This "bird of prey" is a hunter that goes unmatched because they swoop down, seize their unfortunate prey with their taloned feet and rip and tear their meat apart with deadly, sharp, hooked beaks. Despite their enormity, they still manage to fly almost vertically between trees and move with the speed and agility of a gymnast through the forest dodging branches and vines at every turn. They can do this because of their short, but broad wings and squared-off tail. Even though they have a wingspan of 6 feet, they have the rare ability to change their direction of flight very quickly. No other eagle this size has the dexterity to accomplish such an impressive feat as this (Kasnoff 2012, 2, 3; Mogwai 2009, 4).

Monkey-eating Eagles are very clever birds when they hunt. Hunting in pairs, their strategy is to have one rile up a bunch of animals (such as a group of monkeys) creating a distraction while the other sweeps in unnoticed for the kill (Mogwai 2009, 3; Siojo 2008, 15). 

These birds are also disguised very ingeniously with dark brown backs and white underbelly and underwings. From above, they blend in with the ground and from below prey never see them because it is so hard to make them out against the white clouds in the sky (Mogwai 2009, 3).

The Monkey-eating Eagle, found only in the Philippines, has been considered endangered since 2010 when the IUCN, or The International Union for the Conservation of Nature, placed it upon their critically endangered list.(Bhawani 2011, 3). 

(Anonymous G 2008, 1)

The main cause of their endangerment is the loss of their natural habitat. A breeding pair of eagles needs 25-50 square miles (65-130 square kilometers) of rain-forest territory to survive. It is estimated that about 80% of Philippine rain forests have been reduced since the 1970's because of intensive logging for commercial development and slash-and-burn farming for agricultural production. Loss of habitat means loss of available prey and tall trees for nesting and raising young (Sace 2011, 4; Reyes 2008, 6; Siojo 2008, 10; Ullrichver 2008, 2, 9; Kasnoff 2012 4; Anonymous A  2011, 3).

Pollution is another reason for the birds' critical decline. Pesticides and toxic heavy metals which are in the plants get eaten by the herbivores, then by small carnivores and omnivores, and so on and so forth until it reaches the Monkey-eating eagle. Since there are no other predators in the Philippines, evolution has naturally made it the top of the food chain. Therefore, all of the poisonous materials build up until finally the amount is just too much and  the bird dies (Sace 2011, 4; Kasnoff 2012, 4).  
Poachers are yet another problem. Its astounding size, rarity, and beauty are alluring qualities that lead the Philippine eagle to be captured for zoos, bird collectors, and private collectors all at a high price. Beginning in the 1960's young eagles would even be taken from their nests to be sold to the highest bidder (Sace 2011, 4; Kasnoff 2012, 4).

Hunting is the last reason why Monkey-eating eagles are disappearing. As they are predators, these eagles have been known to eat livestock and small mammals. So naturally, many people, in an effort to save their animals, eliminate competition for food, will hunt the eagles down. Not only were they hunted out of necessity, but others killed them for sport. Considered a trophy among hunters, when firearms were made available after World War I, even more eagles were killed (Sace 2011, 4; Kasnoff 2012, 4).

Today, researchers have discovered much about this species. In one study, scientists estimated the amount of Philippine eagles in the island of Mindanao. By using data from 1991-1998 and the amount of suitable forest area, they found the mean distances between breeding pairs and nests to be about 12.47 km apart. This led them to the conclusion that there must be about 82-233 breeding pairs left (Bueser et. al. 2003, 1).

In Amadon's (1964) studies, he founds that the evolutionary trend seems to be producing few young, but giving longer care. This is thought to be because the larger, long-lived birds need more time to develop flight and food getting skills that will enable them to survive. Therefore, the eagles that produce the young with the best abilities contribute more to future generations. Territorial behavior has also evolved into safeguarding food during nesting season to encourage productivity (Amadon 1964, 1, 2).

Another study was done on their breeding behaviors and diet. It was seen that there are eight specific courtship displays and several activity patterns during the nesting period. Two months before egg-laying, copulation would occur until the first month of incubation averaging at about 5 copulations a day. The male provided mainly civet cats and flying lemurs for his mate and chick (Ibanez et. al. 2012, 1).

In Gamauf's (1998) study, Monkey-eating eagles were found to be similar to other raptor species. So observations were made, and they saw that the juveniles' white plumage was very similar to the Barred Honey-buzzard, Oriental Honey-buzzard, Rufous-bellied Eagle, Philippine Hawk eagle, and the Philippine Serpent Eagle (Gamauf et. al.1998, 3, 4).

Researchers from the University of Michigan isolated DNA from blood samples of birds of prey in the family Accipitridae. The results were very surprising. At first, it was thought to be more closely related to the larger raptors such as the Harpy Eagle, Crested Eagle, and the New Guinea Harpy Eagle because of their similar size, habitat, and habits. Although related genetically, the similarities were due to convergent evolution. Instead the smaller snake eagles are now believed to be their closest relative (Lerner et. al. 2005, 1, 2, 3, 4; Siojo 2008, 4).

There is an interesting Philippine story about the eagle. There were once two poor, starving brothers. Every day, their mother would send them out to collect wood for her fires. But it was never enough. One day there would be too little, or it burned too much, or it burned too little, until the boys were so thin from working so hard to find the right kind of wood for their mother. So one day,  they set out and one of the brothers climbed up a tree to cut off some branches. He called out to his brother saying that here was some wood. And it was his arm. Then he called down saying here is more and down came the other arm and so on until all of the bones in his body were on the ground. The boy had turned into an eagle. So the other brother brought the "wood"  to their mother and frightened, she ran away. The eagle circled round her head calling that he did not need her food anymore ( Cole 2012, 1).

The monkey-eating eagle, is just one of many creatures that humans have succeeded in diminishing. Whether by poaching, destruction of habitat by deforestation or by pollution, humans are unwittingly altering the balance of nature. Found only in several areas in the Philippines, there are only a few hundred left of this magnificent creature, surviving more is captivity than in the wild. Not only are these eagles beautiful and magnificent, but they play a major role in keeping the balance of creatures. We cannot know for sure what will happen if we lose any more of the top predators in our ecosystem. We need to be aware that animals have their roles which they need to play to keep the ecosystem in equilibrium. Sixty-five millions years ago, we lost a magnificent group of creatures-the dinosaurs. Up to this point, we can only theorize the real reason why they slowly disappeared. Theories include flood, insects, asteroids, or even blacking out of the sun. Needless to say, all these theories are caused by changes in the status quo of the ecosystem. If we as humans do not do our role as stewards of our environment, if we do not preserve the role of each and every species, it may not be an animal species we lose next, it may be our own life we lose.

Anonymous A. 2011.Natural History Notebooks: Philippine Eagle [homepage on the Internet]. Canadian Museum of Nature. [cited 2012 Mar. 28]. Available from:

Anonymous B. 2012. Facts about Philippine Eagles [homepage on the Internet]. Facts N Facts. [cited 2012 Mar. 28]. Available from:

Anonymous C. 2009. Pithecophaga jefferyi [homepage on the Internet]. IUCN Red List of Threatened Species. [cited 2012 Apr. 28]. Available from:

Anonymous D. Map of Philippines [homepage on the Internet]. 2012. [cited 2012 May 6]. Available from

Anonymous E. 2011 Oct. 7; 4 02 am Near-extinct Philippine eagle shot dead. In: SKNVibes [discussion list on the Internet]. [cited 2012 May 6]. 1 p. Available from: 

Anonymous F, author.; 2009 Oct. 17 published. 5:30. The Philippine Eagle and his Keeper [video].

Anonymous G, author.; 2008 Aug. 18 published. 1:45. The Philippine Eagle [video].  

Amadon. The Evolution of Low Reproductive Rates in Birds, Evolution 1964; 18 (1): 105- 110.            

Bhawani. 2011 Dec. 22. Animals Camp Monkey-Eating Eagle [homepage on the Internet]. Animals Camp; [cited 2012 Mar. 28]. Available from:                   

Bueser et. al. 2003. Distribution and nesting density of the Philippine Eagle Pithecophaga jefferyi on Mindanao Island, Philippines: what do we know after 100 years?, Ibis; 145 (1): 130-135.   

Cole. 1916. Philippine Folklore Stories [homepage on the Internet]. Sacred Texts. [cited 2012 Apr. 15]. Available from:    

Cruz. 2009 May 6. Monkey-Eating Eagle [homepage on the Internet]. Wazzup Manila; [cited 2012 Apr. 7]. Available from: eagle/2415/.  

Diana. 2011 June 8; Philippine Eagle Week 2011. In: Phil-Am Food and Wordpress [discussion list on the Internet]. [cited 2012 May 6]. 1 p. Available from:                 

Gamauf et. al.. Distribution and field identification of Philippine birds of prey: 1. Philippine Hawk Eagle (Spizaetus philippensis) and Changeable Hawk Eagle (Spizaetus cirrhatus), Forktail 1998; 1-11.

Ibanez et. al.. 2012. Notes on the Breeding Behavior of a Philippine Eagle Pair at Mount Sinaka, Central Mindanao, The Wilson Bulletin; 124 (1): 333-336.            

Kasnoff. 2012. Philippine Monkey-eating Eagle: An Endangered Species [homepage on the Internet]. Bagheera. [cited 2012 Mar. 28]. Available from:

Lerner et. al.. 2005. Phylogeny of eagles, Old World vultures, and other Accipitridae based on nuclear and mitochondrial DNA, Molecular Phylogenetics and Evolution; 37 (2): 327 - 346.

Mogwai. 2009 Aug. 5. Monkey-eating Eagle Facing Extinction: Only 500 Remain of this Popular Bird Species [homepage on the Internet]. Orato Media. [cited 2012 Apr. 1]. Available from:

Nigge. 2012; [homepage on the Internet]. [cited 2012 May 6]. Available from:

Reyes. 2008 June 25. The Vanishing Monkey-eating Eagle [homepage on the Internet]. Scienceray. [cited 2012 Mar. 30]. Available from: 

Sace. 2011 May 19. Information on the Endangered Philippine Eagle [homepage on the Internet]. Bright Hub. [cited 2012 Apr. 1]. Available from:

Siojo. 2008. Facts About the Philippine Eagle - The Monkey-Eating-Eagle [homepage on the Internet]. Knoji. [cited 2012 Mar. 28]. Available from:

Ullrichver. 2008 Feb. Philippine Eagle [homepage on the Internet]. National Geographic Society. [cited 2012 Apr. 1]. Available from: