White-bellied heron a species on the verge of extinction: Ensemble model reveals loss of habitats and resultant prolonged isolation driving the species to extinction

Abstract

Habitat degradation and loss have affected many species across all major groups in India and elsewhere. However, the water birds are among the most impacted in terms of habitat loss and drastic decline in populations. The White-bellied heron (A. insignis) (WBH), a Critically Endangered and top conservation priority species, has lost much of its habitat throughout its range and restricted to small and isolated forests habitats. Hence, we attempted to evaluate the changes in habitat and area of occupancy in its entire distribution range using a binary ensemble of both past and present models. We observed a drastic loss in the habitat of WBH by 59.18% in the last century, out of which the novel niche occupied, was around 12,139 km2 in the northern undisturbed areas. The Centroid shift in its range reveals a notable shift in the north and north-eastern areas current in relation to its past distribution. The loss of suitable areas was highest in its range in India, followed by Myanmar and Bangladesh. Whereas in the present scenario, northern areas of Bhutan tend to become more suitable for the species (60% gain), and species may occupy novel niches in the northern region of Bhutan. The Precipitation of Warmest Quarter (bio_18), water runoff in the river and human footprint in its habitat were the significant predictors of the species habitat in the past and present scenario. We speculate that the species might lose some of the evolutionary traits meant for group foraging fish-eating birds because of this shift in range. The species largely occupy forested areas along the fast-flowing rivers such as Namdapha and Lohit in Arunachal Pradesh. We hypothesize that prolonged isolation by sticking to fast-flowing rivers only inside remote areas without much interaction from other group foragers driving WBH to extinction in India and possibly across its range.