The large bird to the right of the nest is a pigeon that was delivered sometime on the 6th of March. Mom has been off the egg and out of sight throughout the late afternoon. Because the camera is zoomed in tight it is impossible to tell if she is perched nearby.
The dead pigeon sitting only inches from the egg is interesting. Many birds eat away from their nests until the eggs hatch. Peregrines for example almost always leave their nests to consume food during the egg incubation phase. One of the ways that you know peregrine eggs have hatched is that you can see the parents bringing food directly into the nests. These red-tails are a different case altogether---throughout the past three seasons their nests have regularly been litered with the remains of their prey. I am always amazed by how wild eggs can survive even in the most filthy of environments. I have monitored peregrine nests where the parents literally laid their eggs on a bed of pigeon feces. Yet the eggs seem to hatch just fine. When we raise wild bird eggs in captivity even the slightest contamination in the incubator often leads to failure.
The fact that mom is off the nest for an extended period is not necessarily cause for alarm. Wild bird eggs can tolerate significant amounts of cooling. It typically only slows the rate of development unless it is truly prolonged. Eggs are much more vulnerable to overheating where an increase of even a few degrees above normal can cause failure. The parents may not begin incubating in earnest until the entire clutch is laid.