Bird O'clock

Unveiling the Mysterious Habits of the Black-billed Koel

The Black-billed Koel, Eudynamys melanorhynchus, is a bird species that belongs to the cuckoo family and is widely distributed in tropical Asia. This bird is known for its distinct plumage, unique vocalizations, and interesting breeding habits.

If you’re curious about this fascinating bird, read on to learn more about its identification, plumages, and molts.

Identification

Field

Identification: The Black-billed Koel can be easily identified by its glossy jet-black plumage, long tail, and bright red eyes. The male is slightly larger than the female, measuring around 43 cm, while the female measures around 38 cm.

Both sexes have a distinctive black beak that helps in differentiating them from other koel species. Similar Species: The Black-billed Koels can be easily confused with the Asian Koel, especially during the non-breeding season where both male and female have similar plumage.

However, the Black-billed Koel is smaller than the Asian Koel, and the male’s tail is shorter, while the female has a shorter crest.

Plumages

The Black-billed Koel has several plumages throughout its life cycle. When the juvenile birds hatch, they have cream-colored down feathers.

After about a week, their feathers turn brown, and they start to develop the black feathers on their head and body. By their third week, they are almost fully feathered and have a dark beak.

The juvenile plumage is similar to the female plumage. The adult female plumage is predominantly brown, with rufous or chestnut streaks on its underside.

Its head and beak are black, and it has a long and pointed black crest. The male plumage is entirely jet-black, with no visible streaks or markings, and it has a shorter crest than the female.

Black-billed Koels have a unique iridescence that occurs when sunlight hits their black feathers from certain angles, making them shine with different colors.

Molts

Like other birds, Black-billed Koels molt their feathers annually. During the molting season, birds shed old and damaged feathers and replace them with new ones.

Molting also triggers changes in plumage colors and patterns. Most birds undergo a complete molt, where they replace all their feathers, but some birds undergo a partial molt, where they only replace certain feathers.

The Black-billed Koel undergoes a partial molt, where they replace their body feathers in a sequence, starting from their head towards their tail. This process usually takes several months.

During this period, it is common to see Black-billed Koels with patchy plumage some parts of their body will have new feathers, while others will still have old ones. This process can affect their flight and make them more vulnerable to predators.

Conclusion

The Black-billed Koel is an intriguing bird species that is fascinating to observe. Identifying them requires a keen eye for details and knowledge of their unique features.

Their various plumages and molting process add to their charm. Observing the process of molting and the different stages of plumage that the Black-billed Koel go through, makes it a pleasure to watch.

Whether you’re a bird enthusiast or just someone who enjoys observing nature, encountering a Black-billed Koel is an experience that you won’t forget.

Systematics History

The Black-billed Koel, Eudynamys melanorhynchus, belongs to the cuckoo family and has been subject to taxonomic revisions over the years. Initially, it was classified as a subspecies of the Common Koel but was later separated due to differences in vocalizations, plumage, and morphology.

In 1818, Johann Friedrich Gmelin named it Cuculus melanorhynchus, which stands to date.

Geographic Variation

The Black-billed Koel exhibits geographic variation in terms of their size and plumage. Birds from the southern parts of its range tend to be smaller and have darker plumage than those in the northern regions.

Additionally, females in southern regions have chestnut-colored plumage, while those in northern areas have rufous-colored feathers.

Subspecies

There are five recognized subspecies of the Black-billed Koel:

1. Eudynamys melanorhynchus melanorhynchus – This subspecies is found in southern India, Sri Lanka, and the Maldives.

2. Eudynamys melanorhynchus kelaarti – This subspecies is found on the southern tip of Sri Lanka.

3. Eudynamys melanorhynchus bourdilloni – This subspecies is found in the Andaman and Nicobar Islands, Thailand, and Indochina.

4. Eudynamys melanorhynchus microrhynchus – This subspecies is found in Sumatra, Java, Bali, and Borneo.

5. Eudynamys melanorhynchus polonicus – This subspecies is found on the Philippine Islands.

Related Species

The Black-billed Koel belongs to the genus Eudynamys, which has eight known species. The other species are:

1.

Asian Koel (Eudynamys scolopacea)

2. Philippine Koel (Eudynamys luzonica)

3.

Moluccan Koel (Eudynamys cyanocephala)

4. Long-tailed Koel (Eudynamys taitensis)

5.

Brown-backed Kokako (Eudynamys melanorhynchus)

6. Pacific Koel (Eudynamys orientalis)

7.

Silver-eared Mesia (Eudynamys melanorhynchus)

8. Blue-headed Chirathia (Eudynamys melanorhynchus)

Historical Changes to Distribution

The Black-billed Koel’s range extends over southern India, Sri Lanka, Indochina, Philippines, Malay Peninsula, Sumatra, Java, Bali, Borneo, and the Andaman and Nicobar Islands. Over the years, the distribution of this species has undergone several changes.

Historically, the Black-billed Koel was widespread in the Indian subcontinent. However, in recent years, its distribution and abundance have declined due to habitat loss and fragmentation.

It is still found in some urban areas, where it benefits from the presence of fruiting trees.

In Sri Lanka, the Black-billed Koel is commonly found in lowland forests and urban areas but is less common in the hill country.

Its presence in Sri Lanka was widely reported in the early 1900s, but its habitat has since declined due to deforestation. In Indochina, the Black-billed Koel is found in Vietnam, Cambodia, and Laos.

This species is currently listed on the Vietnam Red Data Book as a threatened species due to habitat loss and hunting. In the Philippines, the Black-billed Koel is a relatively common bird found in lowland forests, scrublands, and rural areas.

However, its habitat is under threat from deforestation. In Indonesia, the Black-billed Koel is widespread in Sumatra, Java, and Bali.

In Borneo, it is found in the lowlands and up to elevations of around 1700 meters. Additionally, the Black-billed Koel is a vagrant to the Maldives, where it was observed for the first time in 1953.

Since then, there have been several sightings on the islands.

Conclusion

The Black-billed Koel remains a fascinating species for ornithologists due to its morphological, vocal, and behavioral characteristics. Its historical distribution has witnessed several changes due to habitat loss and fragmentation, presenting a challenge for conservationists.

Further research is required to gain insights into the population status of the different subspecies and the species as a whole.

Habitat

The Black-billed Koel is a tropical bird species that inhabits a variety of habitats, including forests, degraded forests, rural gardens, and urban areas. In Malaysia, it is commonly found in lowland dipterocarp forests and wooded areas up to elevations of around 1500 meters.

In Indonesia, it is found in primary and secondary forests, cultivated areas, and mangrove forests. In the Philippines, the Black-billed Koel inhabits scrublands, lowland forests, and rural areas, while in Sri Lanka, it is found in lowland forests and urban gardens.

The Black-billed Koel’s range also extends to urban areas, where it benefits from the presence of fruiting trees.

Movements and Migration

The Black-billed Koel is a sedentary bird species in some parts of its range, while in other areas, it exhibits seasonal movements and migratory behavior. In India, the Black-billed Koel is resident, and its movements are mainly altitudinal.

During the non-breeding season, it moves to lower elevations and can be found in urban areas, sometimes in significant numbers. In the Philippines, the Black-billed Koel is considered resident and non-migratory.

However, there are reports of seasonal movements, suggesting that some birds may undertake dispersal movements depending on food availability. In Indonesia, the Black-billed Koel is also considered non-migratory but exhibits seasonal movements depending on fruit availability.

For example, in Sumatra, the Black-billed Koel can move between highland and lowland forests in search of fruiting trees. In Sri Lanka, the Black-billed Koel is resident and does not undertake long-distance migrations.

However, there are reports of seasonal movements within the country, with birds moving from the lowlands to the hill country during the non-breeding season. Some populations of the Black-billed Koel in Southeast Asia are migratory, with birds moving from breeding grounds to non-breeding areas in the winter.

Birds in the Andaman and Nicobar Islands are known to undertake altitudinal movements, moving from higher elevations to the coast during the non-breeding season. Overall, the Black-billed Koel’s movements and migrations are primarily influenced by food availability, with birds moving to areas where fruiting trees are abundant.

The species’ tolerance for different habitat types allows it to persist in degraded forests and urban areas, where fruiting trees are often present, contributing to its adaptability to different environments.

Conclusion

The Black-billed Koel’s adaptability to a range of habitat types allows it to persist in different environments, including urban areas, making it an accessible bird species for bird watchers and ornithologists. Its sedentary lifestyle in some parts of its range and seasonal movements and migration in other areas reflect its dependence on food availability.

Protecting the forests and fruiting trees that the Black-billed Koel depends on is essential for its conservation, and further research is required to gain insights into the species’ movements and migration within and between countries.

Diet and Foraging

The Black-billed Koel’s diet is primarily frugivorous, feeding on a variety of fruits, including figs, guavas, and papayas. Although their diet is predominantly fruit-based, they also consume insects, larvae, and caterpillars.

They prefer ripe fruits, which are soft and easily crushed by their beaks.

Feeding

The Black-billed Koel forages for food in trees and shrubs. They use their beaks to pluck fruits that hang suspended from branches and leaves.

They may also use their beaks to rip open the fruits and eat the flesh inside. They have been observed eating fruits that are almost as large as their own body.

Diet

The Black-billed Koel’s diet varies depending on the availability of food in different regions and seasons. In India, they feed on figs, while in Indonesia, they consume large quantities of guavas.

They are known to feed on over 80 different types of fruit, making them an important seed disperser in tropical forests.

Metabolism and Temperature Regulation

The Black-billed Koel’s metabolism and temperature regulation are adapted to their foraging and feeding behavior. They have a large crop, which allows them to store food for later digestion.

This adaptation is particularly useful during times of fruit scarcity, where they store excess food in their crops to maintain their energy levels. Additionally, the Black-billed Koel is exothermic, meaning that their body temperature is regulated by the environment rather than internally.

This adaptation allows them to conserve energy when food is scarce and regulate their body temperature in hot tropical environments.

Sounds and Vocal

Behavior

The Black-billed Koel’s vocalizations are striking and considered to be one of its most distinctive features. The male’s call is a melodious, repetitive “koo-o”, while the female’s call is a series of harsh, whistling notes.

Their vocalizations are used for communication and attracting mates.

Vocalization

The Black-billed Koel’s vocalizations are particularly noteworthy during the breeding season. The male’s call is a clear, ringing sound that can be heard for long distances.

It is usually heard in the early morning hours and may contribute to their territorial defense. During the breeding season, males also sing songs to attract females.

The female’s call is more raucous than the male’s and is used to communicate with other females. They may also use their calls to discourage males from approaching them, especially during the non-breeding season.

Young Black-billed Koels also make vocalizations, which are used to communicate with their parents. Their vocalizations are softer and weaker than the adults and are often ignored by other adults in the area.

Conclusion

The Black-billed Koel’s frugivorous diet and foraging behavior allow it to play an essential role in seed dispersal in tropical forests. Their crop size and exothermic metabolism are adaptations that help them conserve energy and regulate their body temperature when food is scarce.

The Black-billed Koel’s vocalizations are unique, with the male’s melodious call serving as a territorial defense and a means of attracting mates. Further research is required to gain more insight into the Black-billed Koel’s vocal behavior and the role it plays in communication and breeding behaviors.

Behavior

The Black-billed Koel’s behavior is characterized by various locomotion styles, self-maintenance, agonistic behavior, and sexual behavior.

Locomotion

The locomotion style of the Black-billed Koel is perching; they are primarily arboreal and are adapted to moving through the forest canopy. They are not strong flyers and rely on their short, rounded wings to maneuver through the treetops.

Self Maintenance

The Black-billed Koel is known for its self-maintenance behavior, particularly in preening, a crucial activity for the maintenance of feathers and maintaining the health of the bird. Preening takes place daily, and Birds use their beaks to distribute preening oil and clean their plumage.

Agonistic

Behavior

Black-billed Koels have a social hierarchy, and squabbles are frequent between individuals. This behavior intensifies during the breeding season when males compete for females.

They engage in chasing, posturing, or other agonistic behaviors. Sexual

Behavior

The Black-billed Koel’s sexual behavior is characterized by elaborate courtship rituals during the breeding season.

The male courts the female through displays of plumage, vocalization, and the offering of fruit or insects. The female usually lays her eggs in the nest of other bird species, where the Black-billed Koel chick is raised as a brood parasite.

Breeding

The Black-billed Koel’s breeding cycle is linked to the onset of the monsoon season. This period coincides with an abundance of fruit, which provides a reliable food source for the birds.

The breeding season typically starts in the late spring and peaks in June as the monsoon rains begin. The Black-billed Koel does not build its nest; instead, it lays its eggs in the nests of other bird species and relies on them to raise the young.

The female selects a host nest that is compatible with the size of an adult Black-billed Koel, and lays one or two eggs. The eggs are laid approximately one day apart, and incubation lasts around 13 to 14 days.

Once the eggs hatch, the Black-billed Koel chick begins to compete with the host’s chicks for food and attention. The Black-billed Koel chick usually hatches first and is stronger than the host chicks.

It may push out the other eggs or chicks from the nest, ensuring that it is the only chick left to be raised by the host parents. The young Black-billed Koel matures quickly and can fledge in as little as 20 days.

Once they have fledged, it is common for them to remain with their host parents for several days before becoming independent.

Demography and Populations

The population status of the Black-billed Koel is not well understood, and there is limited data on its population size. However, habitat degradation and fragmentation are significant threats to the species, and there is evidence of population declines in some areas.

Illegal trade and hunting are also threats to the Black-billed Koel, with the birds being captured for their striking feathers and utilized for traditional medicine. Because of this, the Black-billed Koel is listed as a “Least Concern” species by the International Union for Conservation of Nature and Natural Resources, and measures are required to monitor populations and mitigate threats.

Conclusion

The Black-billed Koel’s behavior is characterized by strong territorial and social behavior during the breeding season, which intensify with greater competition. Their breeding habits are unique, with the species laying eggs into the nests of other bird species.

Threats, such as habitat loss and hunting

Popular Posts