The researchers said there are close ties between duck grazing patterns and rice croppingintensity.
研究员指出，放养鸭子和水稻栽种密度也有密切关联。
2
They looked at five variables: duck abundance, human population, chicken Numbers, elevation and rice croppingintensity.
他们考察了五个变数：鸭丰度，人口，鸡只数量，海拔高度和水稻种植密度。
3
Researchers reviewed three outbreaks in early 2004 through late 2005. They looked at five variables: duck abundance, human population, chicken Numbers, elevation and rice croppingintensity.