The Giant Ibis has a varied diet consisting of invertebrates (particularly locusts and cicadas), crustaceans, small amphibians and reptiles, and seeds. It forages using its long, curved bill to probe into cracks and feel for food deep in the mud or water. Slit-like nostrils are situated at the base of the bill allowing continued breathing whilst the bird’s bill is submerged. In flight, the bird stays low, seldom rising above the tree canopy. Like all ibises, this species is diurnal and prefers to feed in damp substrates, relying on the soft mud around seasonal pools (known as ‘trapeangs’ in Khmer) to survive. These pools are often dug by large animals such as water buffalo. In response to local disturbance and seasonal water-level changes, the bird will range widely to find its preferred feeding conditions. In the absence of damp, submerged habitats, the bird will forage in dry areas. A shy bird, this species nests in trees, often more than 5km from human habitation. They live in singles, pairs or small groups and tend to nest away from villages in deciduous forests located close to grassland and pools.
The decline of the species is primarily due to destruction of habitat, human disturbance and possibly hunting. Wetlands are being drained for agriculture and lowland deciduous dipterocarp forests are being cleared to make way for rubber, sugar cane, cassava and teak plantations. The Giant Ibis is sensitive to human presence. This becomes a problem in the dry season when humans gather at available watering holes, discouraging the ibises from using them. Disturbance at feeding sites, agricultural expansion and hunting, as well as loss of breeding habitat, all contribute to the shrinking population. Recent studies also suggest that nest predation by mammalian carnivores, such as the common palm civet and yellow-throated marten, may be having a huge impact on the Giant Ibis population. A decline in the number of large grazing animals, particularly wild water buffalo, has also been cause for concern, as these birds rely on the pools and wallows dug by the buffalo as feeding sites.
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