This morning we visited the nest about 9:15 and watched for 30 minutes. An adult was on the nest, fluffing its feathers. Before I could get my camera out, it had settled deep in the nest, with the top of its head and the tips of its wings and tail barely visible above the rim. A second adult was roosting in the Australian Pine along the road just west of the nest tree, preening.
My impression is that this bird is rather heavy and its forehead forms a greater angle with the bill than the male. It may be possible that the pair just exchanged incubation duties, based upon their behavior.