Tuesday, September 12, 2006


C D Kaluthota, D K Weerakoon & S W Kotagama
Field Ornithology Group of Sri Lanka, Department of Zoology, University of Colombo

Kumana villu is one of the oldest known breeding sites for many waterbird species that breeds colonially. The canopy of mangrove trees located inside the villu provides nesting facilities for the large water birds such as Painted storks, Spoonbills, Black headed Ibises, egrets, cormorants and globally threatened Spot billed Pelicans. A detailed study of this breeding colony was done in 1983 By Kotagama. After 22 years, the breeding bird survey was reinitiated in July 2005.

First, a roosting count was done to estimate the population size of breeding birds in the Kumana villu. The counts were conducted from 3 pre-identified locations between 1700 to 1900h in the 2nd week of July. Three mangrove vegetation patches of 5000m2 were chosen for a detailed nest count. In each patch, the number of trees used for nesting was recorded. Then for each tree, number of nests, the species to whom the nests belonged, the height of each nest and the current status of nesting were recorded.

Many species of birds use this villu for roosting while Painted Storks showed the highest population density (728). Among other water birds, spot billed pelicans (422), spoonbills (57), cormorants (187), egrets (184), Black headed Ibises (74) and darters (41) are the most common taxa. In 1983, 228 painted storks, 565 pelicans, 125 ibises and 609 egrets were recorded. Five flight paths of birds that come to roost were identified in 1983. However, only 3 flight paths were observed during this survey.

A total of 293 nests were recorded that belonged to five species namely purple herons, little cormorants, painted storks, spot billed pelicans and spoonbills. Most common nesting species in this period was painted stork and 97.6% of their nests were still active. In May 1983, total of 701 nests belonged to seven species were recorded and most nests were of painted storks (529). In 1983, nests of four additional species, grey herons, ibises, egrets and night herons were recorded while purple herons and cormorants were not recorded to be nesting.

The mangrove vegetation has changed from a diverse habitat to a single species (S. caseolaris) stand during last 22 years. Reduction of mangrove area was also observed. Further, invasion of the common weed species Typha angustifolia is another major change that has taken place during this period.

Isolated mangrove trees and trees that are located beyond the perimeter of the villu are not selected by birds for nesting. Low density of vegetation inside the villu is a limiting factor for breeding birds. Most remaining trees in the villu are not in good condition and therefore a replanting programme is recommended to ensure continuous breeding of this colony.

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