Leptoptilos dubius

Geographic Range

Greater adjutants ( Leptoptilos dubius ) are exceedingly rare in their range from Northern India to Indochina and may breed exclusively in the Brahmaputra Valley of Assam. In the early part of the 20th century, large breeding populations of greater adjutants were common throughout Northern India, Bangladesh, Nepal and Southern Vietnam.

• Biogeographic Regions
• oriental oriental
  • native native

Habitat

Greater adjutants ( Leptoptilos dubius ) have been observed in a variety habitats including marshes, lakes and jheels (shallow expansive lakes) as well as dry grasslands and fields. These birds are most frequently associated with slaughter houses and refuse sites near human settlements and were formerly common on the streets and rooftops of Calcutta. They typically nest in large trees and rock pinnacles near human settlements.

• Habitat Regions
• tropical tropical
• terrestrial terrestrial

• Terrestrial Biomes
• savanna or grassland savanna or grassland
• forest forest

• Aquatic Biomes
• lakes and ponds
• temporary pools

• Wetlands
• marsh marsh

• Other Habitat Features
• urban urban
• suburban suburban
• riparian riparian

Physical Description

Greater adjutants are large birds, ranging in height from 120 to 152 cm with an impressive 250 cm wingspan. A long, thick yellow bill precedes the sparsely feathered, yellow to pink head and neck. The head is typically dappled with dark scabs of dried blood and characterized by the presence of a pendulous, inflatable gular pouch. The legs are naturally dark in color but frequently appear ashen due to regular defecation on the legs. When in flight, greater adjutants are recognizable by their white underside feathers and tendency to retract their necks like a heron. A mixture of white and gray feathers, which appear darker during the non-breeding season, adorn the rest of the body. Juvenile greater adjutants resemble adults, but have duller plumage and more feathers around the neck. The mass of these birds is unknown in the wild, but is estimated to be the heaviest of the storks.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike
• ornamentation ornamentation

Reproduction

Other storks are known to be monogamous, but not always paired for life. It is thought that greater adjutants follow this mating system. Great adjutants are colonial nesters and will build many nests in the canopy of a single tree. Males claim suitable nesting branches and advertise their territory by perching on the branch with bills upward and exhibiting bill-clattering. When females perch nearby, males will present them with twigs as part of courtship. Courtship rituals consist more of courtship postures, where males will hold their beaks close to potential mates or tuck the females heads under their chins. Pairs also perform up-down bobbing motions together.

Greater adjutants nest in large, broad-limbed trees with sparse foliage. This choice of nesting tree is thought to facilitate landing and take-off for the large adult birds. Nests are constructed out of sticks and several pairs will often occupy the same tree. While females lay 3 eggs per season, an average of 2.2 chicks per pair are fledged successfully each year. Both parents participate in incubating eggs until they hatch after 28 to 30 days. Chicks fledge at 5 months of age.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• oviparous oviparous

Both male and female greater adjutants participate in nest building. After the eggs are laid, both parents also incubate the clutch for 28 to 30. The altricial chicks are cared for by both parents until they fledge at 5 months old.

• Parental Investment
• altricial altricial
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • male
    • female
  • protecting
    • male
    • female
• pre-weaning/fledging
  • provisioning
    • male
    • female
  • protecting
    • male
    • female
• pre-independence
  • provisioning
    • male
    • female
  • protecting
    • male
    • female

Lifespan/Longevity

Although the longest lifespan of a captive greater adjutant was 43 years, the longevity of these birds in the wild remains unknown.

Behavior

Greater adjutants are often seen foraging alone or in small groups. In general they are a non-migratory species but some make local movements to winter nesting sites. The name 'adjuntant' comes from their distinctive, military-style gait. Their large wingspans facilitate soaring and they are frequently found near thermals. Due to their hot environments, greater adjutants defecate on their legs and the evaporation lowers body temperature (also known as urohydrosis). As a result of this cooling mechanism, legs of these birds are often stained white with uric acid.

• Key Behaviors
• flies
• diurnal diurnal
• motile motile
• sedentary sedentary
• solitary solitary
• social social
• colonial colonial

Home Range

Little is known about the territory size for greater adjutants. Male greater adjutants will advertise their claim on a suitable nesting branch with beak clattering. They are known to build nests relatively close to one another, so breeding territory size is likely small and limited to a nesting branch.

Communication and Perception

Greater adjutants lack vocal muscles so they rely on unique behaviors and tactile forms of communication to interact with each other. Males often utilize beak clattering to advertise their territory and ward off other males. Males attract mates by presenting them with fresh twigs and later holding their beaks close to the female. Breeding pairs also perform head bobbing rituals that likely reinforce their pair-bond. Like all birds, greater adjutants perceive their environments through visual, auditory, tactile, and chemical stimuli.

• Communication Channels
• visual visual
• tactile tactile
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

In their native range, where they are primarily scavengers of large carrion, greater adjutants are known by the name "hargila," meaning bone swallower. They were once prevalent in Calcutta, where their tendency to consume human corpses left to rot in the streets was valued. One record indicates that a single greater adjutant effortlessly swallowed two buffalo vertebrae, measuring approximately 30 cm in length, in less than five minutes. Greater adjutants are most commonly found scavenging in mixed flocks near human garbage dumps or large carcasses. They can also be seen foraging independently near drying pools where they hunt insects, frogs, large fish, crustaceans and injured waterfowl. When foraging, greater adjutants use a method of tactile foraging where they hold their beaks open underwater and patiently wait for a prey item to swim between the open mandibles.

• Primary Diet
• carnivore carnivore
  • scavenger scavenger

• Animal Foods
• birds
• mammals
• amphibians
• fish
• carrion carrion
• insects
• aquatic crustaceans

Predation

No natural predators have been reported for this species. Unhealthy or young birds are likely preyed upon by local carnivores.

Ecosystem Roles

Greater adjutants are important scavengers of large carrion and likely contribute to sanitation and disease control in the environment. Like many birds, greater adjutants are hosts to avian lice including Colpocephalum cooki and Ciconiphilus temporalis .

• Ecosystem Impact
• biodegradation biodegradation

Economic Importance for Humans: Positive

Greater adjutants are valuable scavengers of discarded human waste, including unburied corpses as well as other large carrion. This service may have a role in preventing the spread of disease.

Economic Importance for Humans: Negative

While greater adjutants pose no threat to humans they are often looked upon with disgust because of their general appearance, habit of defecating on their own legs, as well as diet of carrion.

Conservation Status

Many consider greater adjutants to be the most endangered stork in the world. Captive breeding programs have failed thus far, but efforts to protect natural habitats are active. Unfortunately, their tendency to nest near human settlements may prove fatal.

In the early part of the 20th century, the population size of greater adjutants is said to have numbered in the millions. They were common in Northern India, Bangladesh, Nepal and Southern Vietnam. Beginning in the mid 1980's the population began to decline heavily. Today an estimated 1,000 birds remain and likely breed only in the politically unstable Assam state of northern India. Populations are still declining and the IUCN red list lists greater adjutants as endangered.

Felling of large nesting trees, pollution of freshwater systems and a decline in the disposal of human corpses in public trash dumps are all thought to contribute to the rapid loss of this species. In Assam, recent reports of disease in this species also seems to be a contributing factor in its decline. Results of a survey of Assam residents revealed that only 30% of those polled knew greater adjutants are endangered. Greater community awareness of this unique species may help in its recovery.

Additional Links

Encyclopedia of Life

Contributors

Christina Kwapich (author), Florida State University, Emily DuVal (editor), Florida State University, Rachelle Sterling (editor), Special Projects.

References

Brouwer, K., M. Jones, C. King, H. Schifter. 1992. Longevity and breeding records of storks Ciconiidae in captivity. International Zoo Yearbook , 31/1: 131 - 139.

Elliot, A., J. Del-Hoyo, D. Christie. 1992. Handbook of the Birds of the World. Vol 1: Ostrich to Ducks . Barcelona, Spain: Lynx Edicions.

Price, R., J. Beer. 1965. A Review of Ciconiphilus Bedford (Mallophaga: Menoponidae). The Canadian Entomologist , 97/6: 657-666.

Price, R., J. Beer. 1965. The Colpocephalum (Mallophaga: Menoponidae) of the Ciconiiformes. Annals of the Entomological Society of America , 58/1: 111-131.

Rahmani, A., G. Narayan, L. Rosalin. 1990. Status of the Greater Adjutant (Leptoptilos dubius) in the Indian Subcontinent. Colonial Waterbirds , 13(2): 139-142.

Singha, H., A. Rahmani, M. Coulter, S. Javed. 2003. Surveys for Greater Adjutant Leptoptilos dubius in the Brahmaputra valley, Assam, India during 1994–1996. Forktail , 19: 146- 148.

Singha, H., A. Rahmani, M. Coulter, S. Javed. 2002. Nesting Ecology of the Greater Adjutant Stork in Assam, India. Waterbirds , 25(2): 214-220.

International Union for Conservation of Nature and Natural Resources. 2009. "The IUCN Red List of Threatend Species" (On-line). Accessed February 05, 2010 at http://www.iucnredlist.org/apps/redlist/details/144792/0 .