Bird O'clock

Unraveling the Mysteries of the Pacific Koel: Plumage Vocalization Behavior and More

The Pacific Koel, also known as Eudynamys orientalis, is a bird species commonly found across much of Asia, including the Philippines, Indonesia, and Australia. This fascinating bird species stands out for its distinctive calls and striking plumage.

In this article, we will explore the identification of the Pacific Koel, including its plumage and molts, as well as some similar species.


The Pacific Koel is a medium-sized bird with a striking appearance. They have a long tail and a slender body with a curved bill.

The male birds have a glossy blue-black plumage, while the females have a brown plumage with white spots. They have bright red eyes that add to their unique appearance.



Despite the Pacific Koel being a relatively easy bird to identify, there are other birds with similar plumage. However, looking closely at their features can help differentiate them.

One of the main distinctions is their call. The Pacific Koel has a unique “ku-oo” call that is easily recognizable.

By contrast, other species that are similar in appearance like cuckoos and shrikes have very distinct calls. The Pacific Koel’s call is characteristic of this species and helps birders make a positive identification.

Similar Species

The Pacific Koel shares many aspects of its plumage with other birds, which can make identification more challenging. Often confused with the Shining Bronze Cuckoo, which occurs in similar areas, the Pacific Koel is usually slightly larger and with a longer tail.

Additionally, the Shining Bronze Cuckoo lacks the red eyes of the Pacific Koel.


The plumage of the Pacific Koel undergoes changes based on gender and age. The male Pacific Koel bird has a pure black plumage with green-glossed feathers on its back, reflecting iridescent shades of blue-green to rich purple.

The female birds have brown plumage with white spots on its underparts and neck, with reddish eyes. Young male Pacific Koels initially have the brown plumage of the females, and but transform their looks as it grows older, assuming the black and shiny feathers.


The Pacific Koel undergoes a full pre-breeding molt, usually after breeding, replacing its feathers for a new set. The males assume a new black crown and throat feathers, shiny with green, whereas females get a darker, well-defined breast stripes in winter plumage.

In conclusion, the Pacific Koel is an easy bird species to identify in the field if using its unique ku-oo call or closely looking at its key features. Their plumage, molts, and appearance will help in distinguishing them from other similar species.

Learning these essential elements will make it easier to spot and identify the Pacific Koel. This bird species is a fascinating addition to any birdwatching experience and is a must-see for any avid bird enthusiast.

Systematics History

The Pacific Koel, also known as Eudynamys orientalis, belongs to the cuckoo family Cuculidae. This species is a member of the genus Eudynamys, which contains nine tropical Asian koel species.

The Pacific Koel’s taxonomic classification has undergone several changes due to genetic studies that have helped with the revision of the species.

Geographic Variation

The Pacific Koel is distributed across the Asian region, including the Philippines, Indonesia, Papua New Guinea, and Australia. The koels in these areas demonstrate significant variations in plumage.

The birds residing in Indonesia and Australia exhibit the most significant variation.


The Pacific Koel is divided into a total of ten subspecies, each with its distinct geographic distribution and variation in plumage. These subspecies include:


E. o.

cyanocephalus (Horsfield, 1821) – found in Java and Bali Islands

2. E.

o. orientalis (Linnaeus, 1758) – found in Sumatra, Peninsular Thailand, and Peninsular Malaysia


E. o.

diffusus (Richmond, 1902) – found in Borneo and the surrounding islands

4. E.

o. mindanensis (Steere, 1890) – found in the Philippines


E. o.

proximus (Sclater, 1871) – found in Sulawesi and surrounding islands

6. E.

o. pagensis (Mayr, 1940) – found in Yapen Island and Biak Island


E. o.

cornutus (Gould, 1865) – found in the Solomon Islands and Vanuatu

8. E.

o. keri (Rothschild, 1898) – found in Papua New Guinea, the Admiralty Islands, and Australia


E. o.

cyrus (Mathews, 1911) – found in Langkawi Island, Peninsular Malaysia

10. E.

o. papuensis (Salvadori, 1875) – found in the mainland of New Guinea, islands, and eastern Indonesia

Related Species

The Pacific Koel is part of the Eudynamys genus, which contains eight other species. Some of the closely related species to the Pacific Koel include the Black-billed Koel, Chestnut-breasted Koel, Moluccan Koel, and the Common Koel.

These species have a similar appearance and share the same parasites, but their distribution ranges and plumage patterns vary. Recent molecular studies have suggested that the Pacific Koel may be a sister species to the Moluccan Koel, although further research is needed to confirm this.

Historical Changes to Distribution

The Pacific Koel has undergone significant distribution changes throughout history. British naturalist Alfred Russel Wallace initially collected the Pacific Koel from the Malay Archipelago in the 1850s.

However, the first recorded citation of Pacific Koel in North America was a female specimen collected from British Columbia in the 1960s. Since then, the species has colonized other regions in North America, including Hawaii and California.

While there has been little natural distribution change within the species’ native range, Pacific Koel populations in Australia have demonstrated a rapid increase in range and abundance. This increase is the result of human-mediated introductions.

The first documented introduction of Pacific Koel into Australia was in the 1860s. Since then, the species has established in the northern regions of the country and has recently expanded into southern territories.

The expanding range and abundance of the Pacific Koel in Australia have resulted in significant ecological and agricultural impacts. The birds feed primarily on fruit, and their increasing prevalence has resulted in crop damage.

Additionally, the Pacific Koels’ presence has been associated with declining populations of native Australian bird species. In conclusion, the Pacific Koel is a bird species that has undergone significant taxonomic revisions throughout history.

This species is part of the Eudynamys genus and is distributed throughout the Asian region. Pacific Koels demonstrate significant geographic variation and have ten recognized subspecies.

While there have been minimal distribution changes within their range, the Pacific Koel has undergone a significant expansion into Australia, resulting in ecological consequences.


The Pacific Koel requires the presence of trees near wetlands, forests, and agricultural areas. They prefer open areas with sparse vegetation, including mangroves, woodland, and savannahs.

The Pacific Koels inhabit elevations up to 1,500 meters but tend to occupy the lower elevations of these altitudinal gradients. Moisture availability is a vital factor for the Pacific Koel, and they will often forage in areas with seasonal fruiting trees.

In Australia, they are found in areas with mango trees, berry bushes, and palm trees, while in Indonesia, they inhabit areas characterized by habitat complexity of secondary and primary rainforests. The Pacific Koel nests almost exclusively in tall trees, while foraging for specific fruiting trees and shrubs.

Movements and Migration

The Pacific Koel is known for its ability to migrate long distances following the seasonal availability of fruiting trees. While some populations exhibit a degree of sedentary behavior, many populations undergo seasonal movements.

In Indonesia, the populations are known to undertake seasonal migrations to Sulawesi, Sumbawa, Flores, and Lombok Islands. During these migrations, the birds can travel up to 500 kilometers over open waters.

Migrations and movement patterns of Pacific Koels in Australia are not well understood compared to populations in Indonesia. However, studies suggest that they undertake seasonal migrations in search of specific fruiting trees.

In Australia, the Pacific Koels are absent from the southern regions but are commonly found in northern, northwestern, and eastern regions. The movements and migrations of the Pacific Koel are often influenced by seasonal changes in temperature and rainfall.

In Australia, Pacific Koels follow the availability of fruiting trees, such as figs, berries, and mangoes. During the breeding season, the Pacific Koel occupies a small territory, but following breeding, the birds become highly mobile, traveling in search of food.

They can travel large distances, covering hundreds of kilometers to reach areas with abundant fruiting trees. Research indicates that the Pacific Koel populations in the Solomon Islands, Papua New Guinea, and the Philippines undertake minimal migratory movements.

These populations are thought to be resident, and their movements are limited to short-range foraging and dispersal movements. In contrast, the Pacific Koel populations in southeastern Asia and Indonesia undertake seasonal movements in search of fruiting trees, and some of these movements can be quite substantial.

Populations in Indonesia undergo seasonal movements within and between the islands. While much of the Pacific Koel’s movement and migration patterns remain a mystery, continued research on the species’ ecology and behavior will provide crucial insights into this cuckoo’s life history and help develop effective conservation strategies.

In conclusion, the Pacific Koel’s habitat preference includes trees near wetlands, forests, and agricultural areas. This species tends to prefer open areas with sparse vegetation and requires access to specific fruiting trees to thrive.

The Pacific Koel is capable of undergoing seasonal movements in search of fruiting trees, with differences observed across populations. Continued research on the Pacific Koel’s movements and migrations will aid in the development of effective conservation strategies.

Diet and Foraging


The Pacific Koel is a frugivorous bird and primarily feeds on fruit. They pursue key fruiting trees based on seasonal shifts in fruit availability.

The Pacific Koel even develops digestive adaptations that further enable them to specialize in feeding on fruit. These adaptations include a digestive system specifically designed to digest tough plant material and seeds with an optimal pH of 4.5 to 5.5. The Pacific Koel also forages for insects, primarily for developing nestlings, although this food source is not a dietary staple.


The Pacific Koel’s diet varies by geographic location. Populations in Australia, for instance, commonly feed on fruit from Mango trees, palm trees, and berry bushes.

In Indonesia, the Pacific Koel subspecies feed on the fruit of the Lipstick Palm, while those in Papua New Guinea primarily feed on Burdekin Plums. In general, the Pacific Koel’s diet mainly depends on the dominant fruiting plants in their area, with these preferences influencing how the bird feeds in different locations.

Metabolism and Temperature Regulation

The Pacific Koel uses a combination of mechanisms to regulate its body temperature during feeding and other activities. For temperature regulation during activity, each subspecies exhibits various behavioral and physiological mechanisms.

For instance, some subspecies utilize panting or evaporative cooling through their respiratory system, while others adjust their metabolic rate and peripheral circulatory system. Physiological mechanisms include decreasing metabolic rate or heat production, and increased excretion of heat while panting.

These temperature regulation mechanisms work in concert to conserve energy at times of low calorie intake, burn calories efficiently, and sustain activity during high energy demand periods.

Sounds and Vocal Behavior


The Pacific Koel’s most famous feature is its unique and loud vocalization. During the breeding season, male birds produce a call that sounds like a clear “Ku-oo” or ‘ku-oo, ku-oo.’ These calls play an essential role in species recognition, territory establishment, pair formation, and reproduction.

The female Pacific Koel also has a unique vocalization, but it is less recognizable than the male’s. The Pacific Koel continues its calling throughout the day and is continually monitoring the surrounding environment for responses from other birds.

Studies show that Pacific Koels call out more in areas where other Pacific Koels are present. Consistent with this, during the breeding season, Pacific Koels are more vocal and active around females and other individuals who have established territories.

Various calls are flexible based on different contexts. Calls by male Pacific Koels can convey information such as dominance status, aggression, and even nesting-site quality.

In conclusion, the Pacific Koel, like many other birds, is a dietary specialist. Their adaptations enable them to specialize in fruit as their primary food source while supplementing with invertebrates at selected times of the year.

The Pacific Koel is highly vocal, with male birds producing an easily recognizable and unique call that plays an essential function in territory establishment, pair formation, and reproduction. The Pacific Koel’s vocalization, coupled with its physiological and metabolic mechanisms, enables it to thrive in different climates and landscapes.



The Pacific Koel long legs and curved bills make them well-equipped for climbing and moving through trees. The Pacific Koel’s locomotion behavior primarily occurs in a tree canopy, where they obtain their food from fruiting trees.

Self Maintenance

Self-maintenance behavior is common among many bird species, and the Pacific Koel is no exception. These behaviors include preening and sunbathing.

Preening is essential for maintaining feathers and removing parasites, while sunbathing helps regulate body temperature and maintain the bird’s physical health.

Agonistic Behavior

Agonistic behavior refers to a range of competitive behaviors demonstrated by animals as they seek to establish dominance and defend territory, mates, or resources. The Pacific Koel shows agonistic behavior during breeding season as males compete for females.

These behaviors can include calling, aggression, or displays of dominance.

Sexual Behavior

During the breeding season, male Pacific Koels establish territories and call out to attract females while defending their territory against competing males. When a female Pacific Koel enters their territory and responds to their vocalization, the male will continue to call and follow the female until they mate.

Male Pacific Koels use a variety of vocalizations during and after mating. After breeding, the Pacific Koel’s behavior shifts from territorial to traveling in search of food.


The breeding behavior of the Pacific Koel is regulated in part by the onset of the rainy season. The breeding season varies across different parts of the Pacific Koel’s distribution range.

In Australia, the breeding season typically lasts from October to January, while in Southeast Asia, the breeding season is from April to August. During the breeding season, male Pacific Koels establish territories and call out to attract females.

When a female enters the male’s territory, the male follows and vocalizes to her until she agrees to mate. After mating, the female Pacific Koel lays a single egg in the nest of a suitable host, often a crow or magpie.

The female Pacific Koel will monitor the host nest to ensure that her young offspring receives her proper nutrition, after which the parent will leave the host nest and be independent.

Demographics and Populations

Pacific Koel populations are currently stable and do not have any significant conservation concerns. However, as introduced species in Australia, Pacific Koels have been associated with the decline of some native bird species.

In southeast Asia, the populations of Pacific Koels are currently threatened by the loss of habitat due to deforestation and large-scale land conversion.

Habitat loss has led to reduced populations of fruit trees, the primary food source of the Pacific Koel.

Despite threats to its habitat, the Pacific Koel remains relatively common across much of its range. While limited data is available on population trends for most regions, a recent study in southern Thailand and Peninsular Malaysia noted a 12% decline in Pacific Koel populations over the last 20 years, indicating habitat loss and fragmentation may be one possible threat to the species.

Populations of the Pacific Koel need to be monitored more closely to identify any significant threats as they arise. In conclusion, observations of Pacific Koel behavior suggest that these birds are well adapted to a frugivorous lifestyle and their native habitats with effective breeding and vocalization behaviors.

The Pacific Koel demonstrates agonistic behavior during the breeding season and uses vocalizations to establish territory and attract mates. While not experiencing population decline, habitat loss is observed in some areas, reducing the food source and perhaps resulting in long-term population transformation.

The Pacific Koel is an intriguing bird species that inhabits much of Southeast Asia, Australia, and some Pacific Islands. The species exhibits notable geographic variation, depending on a combination of environmental factors and historical influences.

With its unique and recognizable vocalization, the Pacific Koel can help identify its presence in the area. The Pacific Koels’ frugivorous diet and physiological adaptations reveal the species’ importance in seed dispersal and conservation.

The Pacific Koel’s behavioral traits, such as agonistic and mating behaviors, demonstrate the species’ capacity to maintain a healthy and stable population. While facing some threats due to habitat loss, the Pacific Koel continues to find and adapt to new habitats while establishing territories, mating, and breeding

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