A long time ago I learned the Dutch canon Als de zwaan zingt (“If the swan is singing”). This canon is very well suited for warming-up. Inspired by this, I created a warming-up exercise which can be used in several ways. The melody is like this:

You might sing these notes in parallel fifths:

But you might sing the notes in canon as well:

Another possibily is to sing parallel fifths in canon:

Instead of letting the voice groups enter after a bar, you might let them enter after a half bar:

And this compacted version may again be sung in parallel fifths: