For the first time in 19 years, no heron was sighted in Phochhu and Mochhu which once host highest and oldest known population in the country
By Tandin Wangchuk
The White-bellied Heron (Ardea insignis Hume 1878) is a large heron species of the family Ardeidae, order Pelecaniformes, found in freshwater ecosystems of the Himalayas. It is categorized as critically endangered under the IUCN Red List of threatened species and protected under the Schedule I of Forests and Nature Conservation Act 1995 of Bhutan.
It was listed as threatened in 1988, uplisted to endangered in 1994, and to critically endangered since 2007.
To ensure its protection the Royal Society for the Protection of Nature (RSPN) conducted the 19th White-bellied Heron (WBH) annual population survey early this year and counted 22 herons in the country.
The survey confirmed 19 adults and three sub-adult individuals, which is five less than the previous year.
RSPN said the decrease in population was mainly observed in upper Punatsangchhu basin; Phochu, Mochhu, Adha and Harachhu which were oldest and previously the most abundantly used habitats in Bhutan.
The survey covered all currently known and expected habitats along Punatsangchhu, Mangdechhu, Chamkharchhu, Drangmechhu, Kurichhu, Kholongchhu and major tributaries.
A total of 82 surveyors from the RSPN, Department of Forests and Park Services (DoFPS) and Local Conservation Support Groups (LCSG) were engaged in the survey. For every White-bellied Heron sighted during the survey, observer, date, time, GPS location, count, age, and activity were recorded.
In addition, all bird species sighted during the survey were also enumerated for record and to study the diversity and population trend of associated species within the area. A total of 117 bird species; 59 waterbirds and 58 other species were recorded during the survey.
The distribution of WBH to undisturbed freshwater river systems and its piscivorous feeding behaviour can be easily associated with the health of the ecosystem and pristinely environment. They are the indicators of our freshwater river systems.
Their presence in our rivers indicates the health of the rivers, the fish population, water quality, the health of associated freshwater biodiversity, level of disturbances, pollution, and above all, intactness of our nature.
Research has shown that by protecting them and their habitats, we protect our rivers, waters, landscapes, biodiversity, food, and the livelihoods of the local communities.
RSPN attributes the extremely low and shrinking population of the WBH globally is to human exploitation, disturbances, and loss of riverine habitat.
In Bhutan the bird is threatened by three major challenges across the region one being that habitats are being lost to infrastructure development, agriculture expansion, hydropower projects, extractive industries, and climate change.
It further states that most of the few remaining habitats are increasingly under pressure due to incautious eco-tourism and recreation, diminishing food resources, pollution, fragmentation, forest fires, and both man-made and natural calamities.
Therefore, RSPN states, it is easily foreseeable that such human-made and natural disturbances would lead to the extinction of this highly vulnerable bird if timely conservation interventions are not taken.
Concerning the risk, RSPN, in collaboration with relevant agencies and stakeholders, has been working on recovery of population size through research and surveys of population, nests, feeding habitat, distribution, movement, habitat needs, and associated threats.
“Since the inception of WBH conservation projects at RSPN, the annual population survey has been an annual event and it helps us understand the trend, priority habitats and it is a basis for needful further conservation interventions,” RSPN stated.
The annual population survey effectively covered all currently occupied and potential habitats across the country, dominantly Punatsangchhu, Mangdechhu, Chamkharchhu, Drangmechhu, Kurichhu, Kholongchhu and major tributaries. The whole stretch of potential WBH habitat was divided into 53 priority zones, spanning to more than 800 kilometers.
Of the 10 sites, where herons were recorded this year, 6 falls under Punatsangchhu basin, and four under Mangdechhu basin. For the first time, an individual has been recorded from Chamkharchhu basin. Although its presence is Chamkharchhu was known before, only this year, it has been observed during the annual survey.
Similarly, 64% (14 individuals) of the birds were found in the Punatsangchhu basin, and 46% (8 birds) in Mangdechhu basin. Overall, there is decrease in population by five individuals from the previous year.
The change is population was mainly observed in the upper Punatsangchhu basin; Phochu, Mochhu, Adha and Harachhu which were oldest and previously the most abundantly used habitats in Bhutan.
Unfortunately, for the first time in 19 years, no heron was sighted in Phochhu and Mochhu which once host highest and oldest known population in the country. No birds were also sighted in Kurigongri basin and lower Mangdichhu basin.
There is a noticeable change in local population demographics in key foraging habitats over the years. The population in older habitats; Phochu, Mochhu, Punakha, Zawa, Kamechhu, Adha, and Nangzhina has drastically declined over the surveyed years.
Phochhu and Mochhu areas had eight birds during 2007 and 2008, but none were observed this survey. Similarly, no birds were seen after 2013 in Zawa and the Harachhu area, the oldest nesting site, where 6–8 birds were found before 2008. Overall, population trends are decreasing in Adha, Nangzhina, and proximate areas, which were historically preferred feeding and nesting habitats until 2010. The population in Berti was highest in 2009.
While no birds were seen during the 2010 census, the population in lower basin of Mangdechhu is improving today, particularly in Goling and Tsaidang. In contrast to these declining areas, in recent years, more individuals have been sighted in lower regions of Punatsangchhu and Mangdechhu basins, which are also newly discovered sites.
The survey also recorded that Mithuntar, Dagachhu catchment, Balwani, in lower basin of Punatsangchhu and Tsaidang in lower basin Mangdechhu are the most promising sites with both population trends and nesting sites in sharp increase, today
The first WBH population survey was conducted in 2003, and it has been an annual event since then. Today, the conservation of WBH is not only a flagship program but it is at the forefront of RSPN’s core mandate.