Unlike in the past years, conservationists experienced the biggest jolt when white bellied heron (WBH) this year, refused to produce even a single fledgling. Among the 24 WBH individuals present in the country, only two nests belonging to two families were discovered and none succeeded in producing a hatchling.
White bellied heron (Ardea insignis) is a critically endangered bird because there are just only 200 of them left in the world. It is among the 50 rare bird species that are in the threshold of extinction.
According to the recent report published in the ministry of agriculture and forests (MoAF) website, as usual, the team of researchers and bird lovers, expectant of being able to record the hatching of new WBH fledging were out in the field since February this year. Initially, they were able to spot two nests, which signaled some positive breeding activities.
From among the two nests, researchers sighted the first one at Zhemgang’s Bertichu, a stream which forms the tributary of Mangdechu basin while the second one is spotted in Burichu, another stream that contributes water to Punatsangchu basin.
The report stated that, “While the former nest was used in the previous year, the latter was a new nest.” Hence, having spotted couple of nests in primary habitat of the bird, they were hoping to see at least one chick to hatch.
Unfortunately, the nest spotted in Bertichu was found destroyed due to unknown reasons. With less human disturbance seen in the area, the human intervention was ruled out. Hence, the report assumes the cause to be that of natural predation. “The cases of chicks of the white-bellied heron falling prey to predators like the serpent eagle, pallas fish eagle, osprey, yellow throated martin, and to some small cats was reported in the past,” the report stated.
However, the second nest at Burichu fared a little better than the one in Bertichu. Having laid the eggs, the family of the heron is said to have tried all they could to incubate the eggs. Researchers observed the breeding pair by the nest for long time.
“Despite the breeding pair sitting on the nest till the end of June 2013, the egg failed to hatch,” stated the report.
But when the eggs refused the hatch, the pair had to abandon the nest. “By the first week of July, it was seen that the breeding pair had already abandoned.” The pair left the nest because the infertile egg didn’t even show the sign of hatching. Though the team have seen so much commitment from breeding pair to incubate their lone egg, it was unusual to see such a long sitting on the nest,” the report stated.
Officials opined that due to the fact that the nest was located at the proximity to Wangdue-Tsirang Highway, the vehicular disturbance stressed the breeding pair. Officials didn’t rule out human disturbance in this case. But contradictorily, it is the conservationist and visitors themselves who may be to blame. They said such nature conservation team made several trips on a regular basis to photograph and monitor the nesting site.
It is considered normal not to expect all eggs hatch and produce chicks. Although yet to confirm, the inexperienced breeding couple are also suspected to render their eggs sterile failing to hatch.
The studies done by Royal Society for Protection of Nature (RSPN) in the past pointed out that heron’s chicks normally hatch in April and by July they fledge out of nest.
In Bhutan, heron are found mainly within banks of Punatshangchhu basin and Mangdechu basins. Despite their low occurrence in the world, WBH has its own set of predators. In fact, attacks on birds and their eggs by predators have been cited to be a major cause in their population reduction.
It is also considered that Bhutan forms the largest home with population recorded as on last count at 24.
It is estimated that globally, there are less than 200 birds. In addition, Bhutan is also credited to be the first country where the heron chick have been successfully incubated, hatched and raised in captivity by RSPN.
Researchers in the past concluded that heron eggs hatch in about 31 to 35 days.