What is a kookaburra thinking?

The laugh is not a laugh. It's a territorial call, usually run as a duet or a full family chorus, and the job is to tell every other kookaburra exactly where this family's patch begins and ends. Dawn and dusk are the shifts, which is why it lands at the two times of day you least wanted it.

The judging is real enough though. Kookaburras are kingfishers that gave up on fishing, and they hunt by sitting completely still on a high perch and watching the ground until something moves. Lizards, snakes, insects, the occasional mouse. So a bird that appears to be silently assessing your lawn is, in the most literal sense, silently assessing your lawn.