https://en.wikipedia.org/wiki/Chinese_calendar

The true arrival of autumn is marked by 白露 (Báilù). As temperatures cool, moisture in the air turns into dew on grass and trees during night.

In China

• 鴻雁來, ‘The wild geese come’ – referring to the southward migration of geese.
• 玄鳥歸, ‘The dark birds return’ – ‘dark birds’ refer to swallows.
• 群鳥養羞, ‘Birds stock their hoards’ – i.e. in preparation for winter.