There were nine main large waterbird colonies at Prek Toal in the 2008/9 season. The breeding season started in August 2008, and the last birds left the colonies in June 2009.
The total number of nests counted in the peak surveys in 2009 increased significantly from the previous year for Asian Openbill (2008: 9340 nests, 2009: 11364 nests, confidence interval: 9892-12836). The number of nests of Oriental Darter increased from 5447 (confidence interval: 4745-6149) in 2008 to 7308 (confidence interval: 6537- 8079) in 2009. The number of nests also significantly increased for Lesser Adjutant from 220 (confidence interval: 189-251) in 2008 to 348 (confidence interval: 312-384) in 2009.
Little change of nest numbers for Greater Adjutant, Milky Stork and Spot-billed Pelican were seen between 2008 and 2009. Overall, between 2004 and 2009 the average number of nests per trees has increased steadily for Asian Openbill, Oriental Darter, Lesser Adjutant and Painted Stork, while increasing slightly for Greater Adjutant and Milky Stork, and generally fluctuating for Spot-billed Pelican. The shift towards earlier peak nesting periods observed for Lesser Adjutant, Oriental Darter and Asian Openbill is something that merits further study.
A detailed analysis of the arrival, nesting and departure times of colonies over the past six years could establish whether there are real changes in nesting times for the majority of species, or whether this is simply due to small fluctuations over a relatively long peak breeding period. If this is the result of a real change in bird behaviour, an investigation into the possible causes would be necessary to identify any potential threats for these species.