阿彌陀經要解 1.56

1.56

恐有疑曰：既是淨土，何有眾鳥？故今釋曰：非罪報所生，乃彌陀欲令法音宣流故變化作此諸鳥耳。

Fearing there might be doubts saying, 'Since it is a Pure Land, why are there birds?', it is now explained: they are not born from retributions for sin, but rather Amitābha, desiring that the sounds of the Dharma be proclaimed and spread, transformationally created these birds.