But the link between the drop in chimney swift numbers and chimney loss is not clear.

但是，烟囱雨燕数量的下降和烟囱减少之间的联系尚不清楚。

But the link between the drop in chimney swift numbers and chimney loss is not clear. The flying insects that swifts eat also appear to be declining.

但是，烟囱雨燕数量下降和烟囱减少之间的联系尚不清楚。雨燕捕食的飞虫似乎也在减少。