Asian openbills rely heavily on sight and touch to perceive their environment; however studies involving closely related species such as turkey vultures suggest that they may also utilize olfactory cues. Enlarged olfactory bulbs make olfaction possible. Asian openbills, like other storks, are largely mute due to the absence of syrinx muscles, hence vocalization is minimal. Their calls can be described as a mournful “hoo-hoo” and at very close distances, they can be heard making a low grunting noise. Asian openbills resort to bill-clattering as their primary method for various forms communication. Bill-clattering also serves as an important form of communication during breeding season.
Communication Channels: visual ; tactile ; acoustic ; chemical
Perception Channels: visual ; tactile ; acoustic ; chemical
Asian openbills are largely unthreatened, however several threats exist which can potentially cause their populations to decline. Invasive weed species can choke wetlands, resulting in reduced water flow and drying of wetland habitat. Large animals such as buffaloes tend to destroy wetland habitats and consume many of their resources. Fishing further reduces food sources for Asian openbills. Pesticides used by farmers in agricultural wetlands can increase mortality among members of this species. In addition, farmers use rockets, polythene bags and other harmful devices to scare away storks. Asian openbills are often victims of poaching, which can have detrimental impacts on population size. Reclamation of wetlands by the government for developmental purposes also poses a major threat.
In recent years, several measures have been taken in an effort to conserve Asian openbills. Strict laws have been implemented which prohibit poaching and fishing in wetland areas. The government has also strived to increase public awareness by offering educational classes and transforming wetland reserves into eco-tourism sites. Various conservation committees have been established by former poachers, who have been successful in recruiting other poachers by promising them an alternate source of income. More stringent regulation of developmental undertakings has also been implemented to increase the effectiveness of conservation.
US Migratory Bird Act: no special status
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
Asian openbills carry and transmit H5N1, a form of avian influenza. It is questionable whether Asian openbills have the ability to transmit H5N1 directly to humans. Researchers have hypothesized that this is quite unlikely, as Asian openbills tend to keep a great distance from human civilization. They can contract the virus by coming in contact with fecal matter of infected birds. Once infected, Asian openbills house the virus for long periods of time and transmit it to smaller terrestrial birds which come in contact with poultry frequently. In turn, humans who come in contact with infected poultry are highly susceptible to the virus. However, again researchers that they are an unlikely vector for transmission.
Negative Impacts: injures humans (carries human disease); causes or carries domestic animal disease
Asian openbills produce feces that serve as fertilizer for wetland plants, leading to increases in both the plants and fish and crab populations which feed on them. Fishermen benefit from the abundance of such organisms.The meat and eggs of Asian openbills are regarded as delicacies, and are sold at high prices in the market, enabling poachers to earn substantial profit. Asian openbills also feed on golden apple snails, which are major rice pests in Asia, effectively reducing their populations.
Positive Impacts: food ; produces fertilizer; controls pest population
Asian openbills serve as effective indicators of the ecological health of wetlands. They are also vital components of wetland ecosystems in that they establish significant links in food webs and nutrient cycles. Asian openbills produce fecal matter that is rich in nitrogen and phosphorus, serving as an effective form of fertilizer for wetland plants. This in turn causes substantial increases in fish and crab populations which feed on them. Asian openbills feed on golden apple snails , a major rice pest in Asia, and effectively reduce their populations.
Trematodes (Chaunocephalus ferox) commonly use Asian openbills as a host species. They inhabit the small intestine, producing a series of nodular lesions. Trematodes live in the host up through much of its adult life, producing more severe symptoms with increasing age. Symptoms generally include diarrhea, convulsions, and loss of appetite. The trematodes eventually kill the host. Other trematodes (Echinoparyphium oscitansi) have also been found in the intestinal nodules of Asian openbills. Their pathology in Asian openbills has not been well-studied.
Commensal/Parasitic Species:
Asian openbills are carnivores. Their diet primarily consists of golden apple snails and small aquatic invertebrates such as molluscs, crabs, and worms. Frogs, lizards and snakes, insects, and fish also make up a large part of their diet. Asian openbills leave their colonies from time to time in search of food. They typically feed alone, but may form flocks in areas saturated with food. Asian openbills wade in the water and locate their prey using touch and sight. Sometimes, they are seen stalking their prey in an effort to capture them. In most cases, these storks swallow their prey whole, however, they may use their sharp, pointed lower mandibles to crush hard-shelled prey and extract their flesh.
Animal Foods: amphibians; reptiles; fish; insects; mollusks; aquatic or marine worms; aquatic crustaceans
Primary Diet: carnivore (Molluscivore )
Asian openbills are native to the oriental biogeographic region and are largely found in India, Sri Lanka, and certain parts of Indochina. They occupy their entire native range all year round, migrating to specific destinations during breeding season.
Biogeographic Regions: oriental (Native )
Asian openbills inhabit wetland habitats including flooded fields, shallow estuarine marshes, and lakes with brackish water. Flooded fields are often agricultural areas and serve as rice paddies. Such wetlands are on average 385 to 1100 m above sea level and 10 to 50 cm in depth. Asian openbills are wading birds and as such, require ample amounts of rainfall for moist feeding grounds. Nests are built on tree branches which are usually 15 to 60 ft above the ground.
Range elevation: 385 to 1100 m.
Range depth: 0.1 to 0.5 m.
Habitat Regions: tropical ; freshwater
Aquatic Biomes: lakes and ponds; brackish water
Wetlands: marsh
Other Habitat Features: estuarine
The longest lifespan of Asian openbills in captivity is 18 years. However, in one study, an Asian openbill stork was found to survive for more than 18 years in captivity.
Range lifespan
Status: captivity: 18 (high) years.
Asian openbills are medium-sized storks. They are, on average, 81 cm long with a wingspan ranging from 147 to 149 cm. Their mass has not been well-documented, however, storks typically weigh anywhere from 1.3 to 8.9 kg. Asian openbills have pale white or gray plumage with black wings and a forked black tail. Their legs are red and their bills are a dull, yellow-gray color. A notable feature is their open bill, formed by the downward curvature of their lower mandible, which only meets the upper mandible at the tip. Asian openbills are often mistaken for herons, as are other stork species. Storks generally are of a heavier build and fly with their necks outstretched as opposed to retracted.
Males and females are sexually monomorphic, and are usually distinguished by position during copulation rather than by physical appearance. The young contain traces of brown in their plumage, enabling them to be easily distinguished from adults.
Range mass: 1.3 to 8.9 kg.
Average length: 81 cm.
Range wingspan: 147 to 149 cm.
Other Physical Features: endothermic ; bilateral symmetry
The eggs and nestlings of Asian openbills, are commonly preyed upon by crows, Indian spotted eagles, and monitor lizards. This usually occurs at times when parents are away from the nest during incubation and chick-rearing periods. Asian openbills employ several anti-predator adaptations. Parents take turns incubating and foraging to more effectively defend their offspring from predators. Asian openbills also form mixed colonies with other stork species and waterbirds such as herons to establish safety in numbers. Colonies are isolated from their surroundings in a moat-like fashion and nests are typically built in tall trees to make them more difficult for predators to reach.
Known Predators:
Asian openbills are largely monogamous, however rare cases of polygyny have also been reported. Monogamous pairs typically occupy nesting sites in trees early on during breeding season. Male storks, which arrive at these trees after they are fully occupied are compelled to share nesting sites, hence engage in intraspecific attack. In doing so, they attract several single male storks to join the fight. In the end, a male stork joins the monogamous pair or replaces the male which the female originally mated with. Males in polygynous pairs exhibit displays in the same manner as do those of monogamous pairs. Members of polygynous nests generally share the responsibilities of nest-building, incubation, and caring for offspring in a non-discriminant manner. Polygynous nests are also highly successful in terms of hatching, fledging, and protection against intraspecific attack.
Courtship involves male display of nest-building behavior, a sexually-selected trait. Males do this by showing females potential nesting sites and manipulating materials for nest construction. In doing so, males demonstrate the qualities of their genes and willingness to invest in reproduction. Females choose good nest-builders so they can save energy and maintain good physique to meet the costs of reproduction.
During the mating process, Asian openbills fly near each other, often above one another, and eventually pair. Males and females rest side by side on a branch for hours, pecking each other’s heads and behaving aggressively. During copulation males stand on females backs and touch females necks with their bills while establishing cloacal contact for sperm transfer.
Mating System: monogamous ; polygynous
Asian openbills breed on an annual basis, usually between June and December. Breeding reaches its peak during the monsoon months when there is sufficient rainfall to moisten feeding grounds. Both parents work together to build the nest using leaves, grasses, branches, and twigs. Females lay 2 to 5 eggs per reproductive cycle. Both parents incubate the eggs until they hatch at 27 to 30 days. The nestlings are completely dependent on the parents through fledging at 35 to 36 days and continue to remain dependent until reaching sexual maturity at 60 days. At this time, the nestlings leave the nest and are able to breed within the same breeding season in which they have hatched.
Breeding interval: Breeding season for Asian openbills occurs once each year.
Breeding season: Asian openbills breed from June to December.
Range eggs per season: 2 to 5.
Average eggs per season: 3.
Range time to hatching: 27 to 30 days.
Range fledging age: 35 to 36 days.
Average time to independence: 60 days.
Average age at sexual or reproductive maturity (female): 2 months.
Average age at sexual or reproductive maturity (male): 2 months.
Key Reproductive Features: iteroparous ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; oviparous
Both parents make significant investments throughout the various reproductive stages in a cooperative fashion. During nest-building, males generally gather the construction materials while females defend the nesting site. Both sexes construct the nest together, with the female typically taking charge. After the female lays the eggs, both sexes take turns incubating them while simultaneously enlarging the nest. During hatching, both parents work together to drop the shell and other particles. When the offspring are very young, both parents are continuously present at the nest to protect them from predators and harsh weather conditions. When the offspring become more mature, the parents take turns foraging, however the females spend more time in the nest. Both parents partake in feeding and watering their offspring.
Parental Investment: altricial ; male parental care ; female parental care ; pre-hatching/birth (Protecting: Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female); pre-independence (Provisioning: Male, Female, Protecting: Male, Female)
The Asian openbill or Asian openbill stork (Anastomus oscitans) is a large wading bird in the stork family Ciconiidae. This distinctive stork is found mainly in the Indian subcontinent and Southeast Asia. It is greyish or white with glossy black wings and tail and the adults have a gap between the arched upper mandible and recurved lower mandible. Young birds are born without this gap which is thought to be an adaptation that aids in the handling of snails, their main prey. Although resident within their range, they make long distance movements in response to weather and food availability.
The Asian openbill was described by the French polymath Georges-Louis Leclerc, Comte de Buffon in 1780 in his Histoire Naturelle des Oiseaux from a specimen collected in Pondichery, India.[2] The bird was also illustrated in a hand-coloured plate engraved by François-Nicolas Martinet in the Planches Enluminées D'Histoire Naturelle which was produced under the supervision of Edme-Louis Daubenton to accompany Buffon's text.[3] Neither the plate caption nor Buffon's description included a scientific name but in 1783 the Dutch naturalist Pieter Boddaert coined the binomial name Ardea oscitans in his catalogue of the Planches Enluminées.[4] The Asian openbill is now placed in the genus Anastomus that was erected by the French naturalist Pierre Bonnaterre in 1791.[5][6] The genus name Anastomus is from the Ancient Greek αναστομοω anastomoō meaning "to furnish with a mouth" or "with mouth wide-opened". The specific epithet oscitans is the Latin word for "yawning".[7]
The Asian openbill stork is predominantly greyish (non-breeding season) or white (breeding season) with glossy black wings and tail that have a green or purple sheen. The name is derived from the distinctive gap formed between the recurved lower and arched upper mandible of the beak in adult birds. Young birds do not have this gap. The cutting edges of the mandible have a fine brush like structure that is thought to give them better grip on the shells of snails.[8] The tail consists of twelve feathers and the preen gland has a tuft.[9] The mantle is black and the bill is horn-grey. At a distance, they can appear somewhat like a white stork or Oriental stork. The short legs are pinkish to grey, reddish prior to breeding. Non-breeding birds have a smoky grey wings and back instead of white. Young birds are brownish-grey and have a brownish mantle. Like other storks, the Asian openbill is a broad-winged soaring bird, which relies on moving between thermals of hot air for sustained flight. They are usually found in flocks but single birds are not uncommon. Like all storks, it flies with its neck outstretched. It is relatively small for a stork and stands at 68 cm height (81 cm long).[10][11][12]
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While feeding over snail in Mangaon, Raigad, Maharashtra
In flight over marsh habitat
The usual foraging habitats are inland wetlands and are only rarely seen along river banks and tidal flats. On agricultural landscapes, birds forage in crop fields, irrigation canals, and in seasonal marshes.[13] Birds may move widely in response to habitat conditions. Young birds also disperse widely after fledging. Individuals ringed at Bharatpur in India have been recovered 800 km east and a bird ringed in Thailand has been recovered 1500 km west in Bangladesh.[10][14] Storks are regularly disoriented by lighthouses along the southeast coast of India on overcast nights between August and September.[10] The species is very rare in the Sind and Punjab regions of Pakistan, but widespread and common in India, Sri Lanka, Nepal, Bangladesh, Myanmar, Thailand and Cambodia.[15] It has recently expanded its range into southwestern China.[16]
During the warmer part of the day, Asian openbills soar on thermals and have a habit of descending rapidly into their feeding areas. Groups may forage together in close proximity in shallow water or marshy ground on which they may walk with a slow and steady gait. The Asian openbill feeds mainly on large molluscs, especially Pila species, and they separate the shell from the body of the snail using the tip of the beak. The tip of the lower mandible of the beak is often twisted to the right. This tip is inserted into the opening of the snail and the body is extracted with the bill still under water. Jerdon noted that they were able to capture snails even when blindfolded. The exact action being difficult to see, led to considerable speculation on the method used. Sir Julian Huxley examined the evidence from specimens and literature and came to the conclusion that the bill gap was used like a nutcracker. He held the rough edges of the bill as being the result of wear and tear from such actions.[17] Subsequent studies have dismissed this idea and the rough edge of the bill has been suggested as being an adaptation to help handle hard and slippery shells.[8][18] They forage for prey by holding their bill tips slightly apart and make rapid vertical jabs in shallow water often with the head and neck partially submerged. The gap in the bill is not used for handling snail shells and forms only with age. Young birds that lack a gap are still able to forage on snails. It has been suggested that the gap allows the tips to strike at a greater angle to increases the force that the tips can apply on snail shells. Smaller snails are often swallowed whole or crushed.[18] They also feed on water snakes, frogs and large insects.[19] When foraging on agricultural landscapes with a variety of habitats, Asian openbills preferentially use natural marshes and lakes (especially in the monsoon and winter), and irrigation canals (especially in the summer) as foraging habitat.[13]
The breeding season is after the rains, during July to September in northern India and Nepal, and November to March in southern India and Sri Lanka.[13] They may skip breeding in drought years. The Asian openbill breeds colonially, building a rough platform of sticks often on half-submerged trees (often Barringtonia, Avicennia and Acacia species), typically laying two to four eggs. The nesting trees are either shared with those of egrets, cormorants and darters, or can be single-species colonies like in lowland Nepal.[20] Nesting colonies are sometimes in highly disturbed areas such as inside villages and on trees located in crop fields.[21][13] In lowland Nepal, 13 colonies found in an agricultural landscape had an average colony size of 52, ranging from 5 nests to 130 nests.[13] The majority of these colonies were located on Bombax ceiba trees, with much fewer located on Ficus religiosa and Dalbergia sissoo tree species. Asian openbills preferred trees that were much taller and bigger than trees that were available on the landscape, and selectively used wild and native tree species entirely avoiding species that were important for resources such as fruits (e.g. Mangifera indica) despite such trees being much more common.[22] Religious beliefs have secured important trees such as Ficus species, and agro-forestry has secured the most preferred species, Bombax ceiba, that Asian openbills prefer to locate colonies in lowland Nepal.[22] The nests are close to each other leading to considerable aggressive interactions between birds on neighbouring nests. Both parents take turns in incubation, the eggs hatching after about 25 days. The chicks emerge with cream coloured down and are shaded by the loosely outspread and drooped wings of a parent.[10]
Initiation of nests in lowland Nepal was highly synchronized, with colonies started during July and August. Breeding success at nests in these colonies was impacted by proximity of colonies to human habitation, and the progression of the breeding season.[23] Colonies closer to human habitation had lower success, and colonies initiated later during the breeding season (when flooding of the rice fields had reduced to allow ripening of the crop) had lower success. Number of chicks that fledged from colonies located on trees in agricultural landscapes in lowland Nepal were similar to that observed in a protected, mangrove reserve in eastern India suggesting that agricultural areas are not always detrimental to large waterbirds such as Asian openbills.[23]
Nesting openbills in Nepal took an average of 27 minutes to return to nests with food for nestlings and fledglings.[20] The time taken to find food was most impacted by the location of wetlands around colonies, and the progression of the breeding season. Adults look the least time to return with food earlier in the season when the dominant rice crop was most flooded, and time increased as the rice ripened along with the drying out of the fields.[20]
Like other storks, they are silent except for clattering produced by the striking of the male's bill against that of the female during copulation. They also produce low honking notes accompanied by up and down movements of the bill when greeting a partner arriving at the nest.[15][24][25] Males may sometimes form polygynous associations, typically with two females which may lay their eggs in the same nest.[26]
Young birds at the nest are sometimes preyed on by imperial, steppe and greater spotted eagles.[27] Chaunocephalus ferox, an intestinal parasite, is a trematode worm found in about 80% of the wild populations in Thailand[28] while another species Echinoparyphium oscitansi has been described from Asian openbills in Thailand.[29] Other helminth parasites such as Thapariella anastomusa, T. oesophagiala and T. udaipurensis have been described from the oesophagus of storks.[30][31]
In colonial India, sportsmen shot the openbill for meat, calling it the "beef-steak bird" (although this name was also used for the woolly-necked stork[32]).[33]
The Asian openbill or Asian openbill stork (Anastomus oscitans) is a large wading bird in the stork family Ciconiidae. This distinctive stork is found mainly in the Indian subcontinent and Southeast Asia. It is greyish or white with glossy black wings and tail and the adults have a gap between the arched upper mandible and recurved lower mandible. Young birds are born without this gap which is thought to be an adaptation that aids in the handling of snails, their main prey. Although resident within their range, they make long distance movements in response to weather and food availability.
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