The researchers said there are close ties between duck grazing patterns and rice cropping intensity.

研究员指出，放养鸭子和水稻栽种密度也有密切关联。

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They looked at five variables: duck abundance, human population, chicken Numbers, elevation and rice cropping intensity.

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。

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Researchers reviewed three outbreaks in early 2004 through late 2005. They looked at five variables: duck abundance, human population, chicken Numbers, elevation and rice cropping intensity.

研究人员检查了2004年初到2005末的三次爆发，他们注意到了五个变化的因素：鸭子的多少，人类的人口，鸡的数量，海拔和稻米种植密度。

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