I arrived at the nest at about 12:45 PM today and found one adult deep in the nest. Only the top of its head was visible.
After 15 minutes another adult flew in from the east, carrying some fine nesting material.
The arriving bird seemed to be quite large, and its gape extended well past the middle of its eye, suggesting it was the female. Other observers have noted a "dark spot" on the right side of the female's face. This bird had black smudges at the base of its bill on the right and its forehead was also stained. Ground observations suggest that incubation had commenced about 2-3 days ago. Both were off the nest 4 days previously, which would be unusual if egg-laying had commenced. One observer said that he witnessed an exchange of incubation duties 2 days previously.
The (presumably male) bird stayed deep in the nest for the entire 45 minutes that I observed the nest. The other bird rearranged some nest material and then, after about 5 minutes, flew to roost on the right nest support branch.
This photo shows the roosting bird's prominent halluxes (hind claws), which are longer in the female than the male, but there is no basis for comparison: