"A cooling behavior in which birds rapidly flap membranes in the throat to increase evaporation.
Owls are able to reduce their body temperature in hot weather by "panting" through partially opened bills. This is called "gular fluttering" - gular having to do with the throat area.
Warm air is exchanged ambient air which is drawn into the highly vascular throat where the blood vessels are constricted, thus enabling heat dispersion
Also at high temps, owls may stand erect, droop wings & use gular flutter to self-cool
She is also getting antsy with the upcoming hatch day and may be feeling the movement from inside her egg that is about to hatch