March 13 notes: time for diligence
Look for subtle behaviors in this period. An adult may rise up, step around the eggs, and reach down to roll them with its beak. If a prolonged absence is planned, a departing adult may cover its eggs with nest lining before departure. When resuming incubation, the female is likely to almost go face down before settling into a position where its brood patch is pressed snugly against the eggs. This is a thinly feathered area on the upper breast enabling an incubating bird to transfer most of its body heat to the eggs.
Incubation duty is not as easy as it sounds. On March 12, I watched an incubating eagle at a Penobscot County nest sit tightly while a crow perched on the edge of the eagle nest: an apparent attempt to lure the incubating eagle into aggressive pursuit and perhaps allow other crows nearby to predate the eagle egg(s). This eagle did not budge, and its mate appeared after a 10-minute standoff to chase away the crows. Raccoons and fisher may also climb into lofty eagle nests for eggs or nestlings, and biologists may prescribe a predator guard to deter them.
Management comments: Eagles have varying levels of tolerance to intrusions. If you or I get too close to a nest, an incubating bird may abandon its primary mission of egg care to circle the nest vicinity (often with an exaggerated flapping flight: not the typical, effortless soaring) and vocalize in protest. This behavior can be misinterpreted as "the eagles are putting on a show for us" when, in fact, they are imploring you to leave. Please do so! -- Charlie Todd, Maine Dept. of Inland Fisheries and Wildlife