The population of endangered species is declining in other oldest habitats in the country
Bhutan counted 22 white-bellied herons (WBH) during the recent annual population survey, which is the lowest in five years.
The five-day population survey that ended on March 3 recorded 19 adults and three sub-adult individuals, which has decreased by five individuals compared with 2020.
Sixty-four percent (14 individuals) of the birds were found in the Punatsangchhu basin, and 46 percent (8 individuals) were counted in the Mangdechhu basin.
Of the 10 sighting areas, six fall under Punatsangchhu basin, and four under Mangdechhu basin. An individual has been recorded for the first time in the Chamkharchhu basin.
However, the decrease in population, according to the survey report was observed in the upper Punatsangchhu basin—Phochhu, Mochhu, Adha, and Harachhu—the oldest and previously most abundantly used habitats in Bhutan.
“For the first time in 19 years, no heron was sighted in Phochhu and Mochhu areas that once hosted the highest and oldest known population in the country,” said the chief of species and habitat conservation division with Royal Society for Protection of Nature (RSPN), Indra Prasad Acharja.
Phochhu and Mochhu areas had eight birds during 2007 and 2008.
No birds were sighted in Kurigongri and lower Mangdichhu basins.
The population is also decreasing in Adha, Nangzhina, and nearby areas, which were historically preferred feeding and nesting habitats until 2010.
Eighty-two surveyors from RSPN, the forest department, and local conservation support groups surveyed 53 priority zones, spanning more than 800 kilometres.
The survey covered all currently known and expected habitats along Punatsangchhu, Mangdechhu, Chamkharchhu, Drangmechhu, Kurichhu, Kholongchhu, and major tributaries.
Three live nests were located during the survey, of which two had three eggs each and one pair of herons was found building a nest.
Indra Prasad Acharja said that for every WBH sighted, observer, date, time, GPS location, count, age, and activity were recorded. The survey was conducted using Epicollect5 digital data collection platform.
“Other 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.”
Studies have attributed the decrease in WBH population to habitat loss and damage from infrastructure development, agriculture expansion, hydropower projects, extractive industries, climate change and increasing pressure on habitats. The small population is under crisis with increased mortality and declining breeding success.
The distribution of WBH in undisturbed freshwater river systems and its feeding habits signifies the health of the ecosystem. “WBH presence in rivers indicate 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,” said Indra Prasad Acharja.
WBH (Ardea insignis) is a large heron species found in freshwater ecosystems of the Himalayas. It is critically endangered under the IUCN Red List of threatened species.
In Bhutan, WBH is protected under Schedule I of Forests and Nature Conservation Act 1995. It was listed as threatened in 1988, uplisted to endangered in 1994, and to critically endangered since 2007.
The first WBH population survey was conducted in 2003 and has become an annual event. In the last five years, the highest number was recorded at 28 individuals in 2016.