A roaring lion does not catch any prey.

What it means
A lion that only roars catches nothing; it is the hunt that feeds it. The proverb is said of people who boast about what they will do and never act on it.
Acholi · East Africa
Source and context
From: Acholi, East Africa
Source: Acholi (Uganda, South Sudan) oral-tradition proverb — "African Proverb of the Month," November 2011 (afriprov.tangaza.ac.ke)

The source explains it: This proverb is said of those who boast by words without action. The wording of the meaning is ours.