What is unusual here?

Pilot Joe Duff wrote: "While Chris was training with Cohort One in July, three of the birds dropped to lie in the grass next to the aircraft. They first went down on their hocks with their feet sticking out in front of them. Then they lowered their bodies to cover their legs. It took a couple of seconds, and this was very unusual behavior. Cranes are vulnerable in this position, and they are not normally that relaxed outside the pen.

"Chris and I stared for a few minutes, baffled by this posture. We checked to make sure the birds weren't overheated and trying to cool themselves. We watched for the depression that is evident in a bird too sick to stand. We even taxied the aircraft away and watched them chase after it, checking their gait and steadiness on their legs. As soon as we stopped, the birds were back down on the ground. Finally we realized it was likely an attempt to protect their legs from mosquitoes! They poked at the ground and seemed happy enough enjoying the momentary relief."