The literal observation that ducks are the first to sense the warming of river water in spring, marking the arrival of the season.

所谓春江水暖鸭先知，看那群野鸭在河里游得欢，就知道春天已经到了。

The figurative sense that experts or those directly involved in a field are the first to detect emerging trends or shifts.

春江水暖鸭先知，在这个行业打拼多年的他，最先察觉到了市场的变化。