What's the difference between skirl and skirr?

Skirl

Definition:

• (v. t.& i.) To utter in a shrill tone; to scream.
• (n.) A shrill cry or sound.

Example Sentences:

Skirr

Definition:

• (v. t.) To ramble over in order to clear; to scour.
• (v. i.) To scour; to scud; to run.
• (n.) A tern.

Example Sentences: