Influence of wet and dry seasons on the breeding of barn owl and its relation to rat damage

The effects of wet and dry season paddy crops on the breeding of barn owl (Tyto alba) and its relation to rat damage was studied in the district of Tanjung Karang, Selangor, Malaysia. The first site was at Sungai Burung where the nest box density was one box per 45 hectares of rice field. The second study site was in Sawah Sempadan which involved three experimental plots designed to investigate the effects of nest box density on rat damage, with densities of 1 box per 5, 10 and 20 hectares. The nest box occupancy rates for both seasons were 72.2% but can increase to 83.3% during the wet season crop. Mean clutch size during the dry and wet season crops were 5.38 and 4.07 respectively. Hatching success was 85.7% during the dry season and 79.2% during the wet season. Fledging success for both seasons were greater than 93%. Higher occupancy and hatching success during the dry season crop suggests that T. alba responded in a functional way in dealing with increasing rat numbers. Lower rates during the wet season crop serve to limit population growth of T. alba. Damage levels to paddy crop at Sungai Burung, during the tillering stage for both seasons were less than 2%. Damage levels during the booting and harvesting stages were also < 2% but increased to 3.22% and 3.39% respectively for the dry season crop. Higher crop damage level during the dry season can be associated with limited alternative food sources and the rats rely on paddy as their main food source. Damage levels at Sawah Sempadan were low throughout both crop seasons with mean crop damage levels of 0.65 + 0.10% far the 5 ha/box plot, 0.78 ± 0.28% for the 10 ha./box and 1.57±0.15% for the 20 ha./boxplot. This indicates that higher density ofT. alba at Sawah Sempadan can control rats better throughout paddy crop seasons.