Are you a bird brain?
Do "proud as a peacock," "sitting duck" or "dumb goose" sound familiar? Just like English, the German language often uses birds in language idioms: blinde Hühne (blind hen) and schräger Vögel (an oddball), to name just a couple.
The common sparrow, or Spatz, was once kept by the ancient Romans as a pet. Spatzenhirn derives in part from Gehirn, the German word for brain. Because sparrows have relatively small skulls in comparison to the big birds that roam the wild, it was thought that their intelligence was limited. However, don't underestimate the power of small - sparrows can even swim!
From Spatzen there are idioms with both positive and negative connotations. You might use Spatzi or Spatz as a term of endearment for your children, like little sparrow in English, but should they do something really stupid, then Spatzenhirn it is! It is commonly used with the verb haben (to have) as in "Du hast ein Spatzengehirn!" if you forget this week's word…