Individual study: Effects of rice field management on winter densities of waterbird species in the lower basins of the River Sado and River Tejo, Lisboa / Alentejo, Portugal
Lourenco P.M. & Piersma T. (2009) Waterbird densities in South European rice fields as a function of rice management. Ibis, 151, 196-199
Rice Oryza sativa fields can be an important seasonal habitat for waterbirds. In Portugal, they are drained in September/October to facilitate the harvest, after which stubbles are left standing until they are ploughed or (typically later) burned; the water level over winter depends on a combination of rainfall and agricultural management. This study investigated how water level and straw management affected winter densities of waterbirds using rice fields in 10 study areas in the lower basins of the River Sado (38º29'N, 08º38'W) and River Tejo (38º56'N, 08º51'W), Lisboa / Alentejo, south-central Portugal.
In total, 120 rice fields (covering 280 ha) were selected at random from across the 10 (unnamed) study areas. Numbers of waterbirds present in these fields were monitored during surveys every two weeks between October 2005 and March 2006, and December 2006 and January 2007. During surveys, fields were categorised according to their water level (flooded, moist or dry) and the stage of rice straw management (mature rice, standing stubble, ploughed fields or set-aside fields).
Of the 39 non-passerine species recorded during surveys, only data for the 13 most common species were analysed.
The densities of five species (cattle egret Bubulcus ibis, black-winged stilt Himantopus himantopus, common snipe Gallinago gallinago, lesser black-backed gull Larus fuscus and black-headed gull L. ridibundus) were found not to be affected significantly by any of the field management variables investigated. Unsurprisingly, seven of the remaining eight species (i.e. little egret Egretta garzetta, grey heron Ardea cinerea, white stork Ciconia ciconia, greater flamingo Phoenicopterus roseus, pied avocet Recurvirostra avosetta, northern lapwing Vanellus vanellus and black-tailed godwit Limosa limosa) showed significantly higher densities in flooded fields than in dry and (for all except little egret) moist fields.
Seven species were found to be significantly influenced by the stage of straw management. Little egret, grey heron and white stork showed significantly higher densities in standing stubble fields than in all other types (apart from set-aside fields in the case of white stork). Densities of avocets, black-tailed godwits and common redshanks Tringa totanus were significantly higher in ploughed fields than in mature rice, standing stubble and (except in the case of redshank) set-aside fields. Lapwings occurred in significantly higher densities on set-aside fields than on all other field types.
Note: If using or referring to this published study, please read and quote the original paper, which can be accessed from http://www3.interscience.wiley.com/journal/121410495/abstract.