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The lesser adjutant (Leptoptilos javanicus) is a large wading bird in the stork family Ciconiidae. Like other members of its genus, it has a bare neck and head. It is however more closely associated with wetland habitats where it is solitary and is less likely to scavenge than the related greater adjutant. It is a widespread species found from India through Southeast Asia.
DescriptionEdit
A large stork with an upright stance, a bare head and neck without a pendant pouch, it has a length of Template:Convert (outstretched from bill-to-tail measurement), weighs from Template:Convert and stands about Template:Convert tall.<ref name=hbk>Template:Cite book</ref><ref name=":8">Template:Cite book</ref><ref name="Hancock">Hancock, James A.; Kushan, James A.; Kahl, M. Philip. (1992) Storks, Ibises and Spoonbills of the World. Princeton University Press. Template:ISBN</ref> The only confusable species is the greater adjutant, but this species is generally smaller and has a straight upper bill edge (culmen), measuring Template:Convert in length, with a paler base and appears slightly trimmer and less hunch-backed. The skullcap is paler and the upper plumage is uniformly dark, appearing almost all black. The nearly naked head and neck have a few scattered hair-like feathers. The upper shank or tibia is grey rather than pink, the tarsus measures Template:Convert. The belly and undertail are white. Juveniles are a duller version of the adult but have more feathers on the nape.<ref>Template:Cite book</ref> During the breeding season, the face is reddish and the neck is orange. The larger median wing coverts are tipped with copper spots and the inner secondary coverts and tertials have narrow white edging. The wing chord measures Template:Convert in length. Like others in the genus, they retract their necks in flight. In flight, the folded neck can appear like the pouch of the greater adjutant.<ref name=pcr>Template:Cite book</ref> Males and females appear similar in plumage but males tend to be larger and heavier billed.<ref name= Hancock/><ref>Template:Cite journal</ref>
Distribution and habitatEdit
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The lesser adjutant is often found in large rivers and lakes inside well wooded regions, in freshwater wetlands in agricultural areas, and coastal wetlands including mudflats and mangroves.<ref name=":0" /><ref name=":1">Template:Cite journal</ref> It is found in India,<ref>Template:Cite journal</ref> Nepal,<ref name=":0">Template:Cite journal</ref> Sri Lanka,<ref name=":2">Template:Cite journal</ref> Bangladesh (a colony with about 6 nests and 20 individuals was discovered near Thakurgaon in 2011),<ref>Template:Cite journal</ref> Myanmar, Thailand, Vietnam, Malaysia, Laos, Singapore,<ref name=":1" /> Indonesia and Cambodia.<ref name="Hancock" /> The largest population is in Cambodia. In India they are mainly distributed in the eastern states of Assam, West Bengal and Bihar. It may occur as a vagrant on the southern edge of Bhutan.<ref>Template:Cite journal</ref> They are extremely rare in southern India.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> In Sri Lanka, they are found in lowland areas largely within protected areas, though they also use forested wetlands and crop fields.<ref name=":2" /> In Nepal, surveys in eastern districts had suggested that they preferentially use forested patches with small wetlands, largely avoiding crop fields.<ref name=":0" /> Additional studies, however, are showing the opposite - breeding densities and breeding success of Lesser Adjutant across lowland Nepal are much higher on croplands.<ref name="gopi2016">Template:Cite journal</ref><ref name=":5">Template:Cite journal</ref><ref name=":7">Template:Cite journal</ref>
Behaviour and ecologyEdit
The lesser adjutant stalks around wetlands feeding mainly on fish, frogs, reptiles, large invertebrates, rodents, small mammals and rarely carrion.<ref name="Hancock" /><ref name=":1" /><ref name=":3">Template:Cite journal</ref> Location of prey appears to be entirely visual, with one observation of storks sitting on telegraphic poles apparently scanning a marsh for prey.<ref name="Hancock" />
They are largely silent but have been noted to clatter their bill, hiss and moan at the nest.<ref name="pcr" /> During one of the threat displays called the "Arching display" that is given in the presence of intruders, adults extend their neck and sometimes give a hoarse wail.<ref name=":4">Template:Cite journal</ref>
Courtship behaviour of the lesser adjutant is identical to other species of the genus Leptoptilos. During pair formation, female birds lift their heads in a scooping motion with bill-clattering (called the "Balancing Posture").<ref name=":4" /> They are solitary except during the breeding season when they form loose colonies, never exceeding 20 nests in a single colony.<ref name="hbk" /><ref name="Hancock" /> The breeding season is February to May in southern India and November to January in north-eastern India, beginning as early as July.<ref name="Hancock" /><ref name="fbi2" /> In central lowland Nepal, nesting in 2015 began in July, and new colonies continued to be initiated until November.<ref name=":5" /> The nest is a large platform of sticks placed on a tall tree. In Nepal, nest initiations started in mid-September continuing until mid-November, with all chicks fledging by late-January.<ref name="gopi2016" /> The nest diameter is more than a metre and up to a metre deep.<ref name="hbk" /> The clutch consists of two to four white eggs that are rapidly soiled during incubation.<ref name="Hancock" /><ref name="fbi2">Template:Cite book</ref><ref>Template:Cite journal</ref> Incubation period is 28–30 days.<ref name="Hancock" />
In eastern Nepal, four colonies consisting of 61 nests were all built on the tree species Haldina cordifolia and Bombax ceiba.<ref name=":0" /> In central lowland Nepal, 35 colonies with 101 nests were located on four tree species namely Haldina cordifolia, Bombax ceiba, Ficus benghalensis and Ficus religiosa with the majority of colonies located on Bombax ceiba trees.<ref name=":6">Template:Cite journal</ref> Another study the subsequent year across five locations along lowland Nepal monitored 65 colonies with 206 nests from which 280 chicks fledged, and the most frequently used tree species were B. ceiba, H. cordifolia and F. religiosa respectively.<ref name=":7" /> Other tree species on which nests have been found in India and Myanmar include Alstonia scholaris and Salmalia malabarica with some nests located as high as 46 m.<ref name=":3" /> Nests have not yet been located in Sri Lanka, though young birds have been observed feeding in crop fields and in freshwater wetlands.<ref name=":2" /> The average size of 35 colonies with a total of 101 nests in central, lowland Nepal was 2.9 nests, ranging in size from one nest to 13 nests.<ref name="gopi2016" /> Location of colonies in central lowland Nepal was not related to tree density available on the landscape suggesting that nest trees are still adequate here. However, lesser adjutant storks strongly selected non-domestic trees almost entirely, also preferring trees that were much taller and bigger relative to available trees on the landscape.<ref name=":6" /> Religious beliefs and agro-forestry practices appear to be responsible for retaining trees that are preferred by lesser adjutants for locating their colonies.
Breeding success in lowland Nepal was positively correlated to colony size, possibly due to reduced predation at colonies.<ref name=":5" /> Colony-level breeding success was also impacted by extent of wetlands around colonies, which ameliorated negative impacts of proximity to human habitation. Colonies located on trees in agricultural landscapes of lowland Nepal had a higher breeding success relative to colonies located on trees in forested areas or protected wetland preserves suggesting that current agricultural practices with one season of flooded crops (rice during the monsoon season) followed by winter crops that need some pulsed irrigation (e.g. wheat) are conducive to Lesser Adjutant breeding.<ref name=":5" /> Multi-site evaluations showed Lesser Adjutants used cues such as tree height to locate colonies, with taller trees hosting bigger colonies, which in turn resulted in higher fledging success.<ref name=":7" />
Adult storks took an average of 30 minutes to return to nests with food for nestlings and fledglings, though there was considerable variation in this measure. Time taken to return to nests by adults was impacted by colony size, age of chicks, amount of wetlands around colonies, and the progression of the season.<ref name="gopi2016" /> Adults returned faster when brood sizes were higher, but took longer to return as chicks aged. The breeding season in Nepal extended from the middle of the monsoon, when the primary crop on the landscape was flooded rice, to winter, when the cropping was much more mixed and the landscape was much drier. This variation was clearly represented in the changing amount of time it took adults to return to nest after finding food.<ref name="gopi2016" /> They returned much faster during the monsoon, but took longer when the crops changed and the landscape dried out suggesting that changing cropping patterns can have serious implications on their ability to raise chicks.
A lesser adjutant paired and hybridized with a painted stork at Dehiwala Zoo, Sri Lanka and at Kuala Lumpur Zoo.<ref name="Hancock" /> The hybrid young had plumage and bill-size of the adjutant, but stance and bill shape of the painted stork.
ConservationEdit
The Lesser Adjutants were moved from "Least Concern" to "Vulnerable" in 2020, but this reclassification was based nearly entirely by assumptions that were based on surveys in forested areas. The assumptions asserted that the species was relatively rare, and that it was affected to their detriment by agricultural expansions.<ref name=":0" /> Subsequent work in South Asia, that has been far more detailed and nuanced, with analyses covering robust colony-level and landscape-level evaluations, have shown these assumptions to be incorrect and likely part of generic assumptions that appear to be overlaid on all agricultural areas and birds by scientists in developed countries.<ref name="gopi2016" /><ref name=":5" /><ref name=":7" /><ref name=":6" /> Like for many other large waterbirds, the south-east Asian populations of Lesser Adjutant storks appear to be greatly at risk due to a combination of hunting and habitat destruction.<ref name=":8" /><ref>Template:Cite book</ref> Subsequently, additional research has shown their population sizes to be much higher than previous estimates that were based on guesses. The assertion that this species was declining rapidly was also found to be incorrect given the high breeding success and large number of breeding colonies documented across lowland Nepal. Subsequently, the conservation status of the species was downlisted to "Near Threatened" to more appropriate reflect evidence.
ImagesEdit
- Lesser Adjutants with its nesting at Nehra, Darbhanga, Bihar.JPG
Nesting at Nehra, Darbhanga, Bihar
- Lesser Adjutant in flight at Nehra, Darbhanga, Bihar.JPG
In flight at Nehra, Darbhanga, Bihar
- Lesser adjutant (Leptoptilos javanicus) in Assam JEG0739 a.jpg
In flight at Dadara, Assam