Research on White-bellied heron – Abstract

ABSTRACT

The White-bellied Heron (Ardea insignis) is Critically Endangered species of herons that occur in Bhutan’s river system. Habitat degradation and increased disturbance by human actions are seen as major causes for its population decline in Bhutan and elsewhere in its habitat range. Two major rivers of Bhutan, Punatsangchu and Mangdechu in which the White-bellied Heron occur were surveyed in the month of August and September, 2011. Keeping major rivers and streams as transect, a plot of 400 m² was laid at distance of 500 meters alternately at left and right bank and assessed its feeding areas. The nesting and roosting sites were assessed based on the location and availability of nest or roost trees. A total of 48 plots were laid within the study area and 94 households residing within the 500 meters river buffer were interviewed using structured questionnaires. Four numbers of White-bellied heron sighted during the survey accounted sighting probability of this species during monsoon to 14% and population counting probability of 15%. The habitat model projected Kurichu and Drangmachu as suitable habitat in addition to Punatsangchu and Mangdechu. This projection accounts 0.9% (347.85 km²) of Bhutan’s geographical area as available habitat for White-bellied Heron. Chirpine forest was found dominant habitat components in the entire survey areas (65% of trees counted). More than 90% of the available habitats were found suitable to highly suitable. The mean distance between feeding and nesting sites was 248.25 meters. The nests are found on tall chirpine trees rooted on slopes of 35⁰ to 48⁰. The average distance from river to roosting areas (trees) was 418.54 meters and trees are found on mean slope of 29.12⁰. Large chirpine trees are preferred for both nesting (Mean DBH = 67.62 cm and mean height = 29.5 m and roosting (mean DBH = 67.70 cm and mean height = 28 m). More than 71% of the areas surveyed are projected with low to moderate threats. Riverbed Quarry and livestock grazing are major contributing factor for habitat degradation (p = .000, p = .000 respectively). Logging and forest fire are highly correlated threat factor that exhibit high intensity of habitat degradation. The bridge and footpath are significant disturbance factors (p = .000 and p = .001 respectively). The local people’s perception survey indicates some level of social value (43% of the respondent) attached to this bird but extremely low cultural value (9% of the respondent). People have shown high support for conservation initiatives required for the protection of this bird (91% of the respondent).