While we were having equipment problems, our camera zoom was set half-way out, rather than zoomed tightly on the nest box, and we recorded several copulations on the nest ledge. Each time, the pattern was the same. Bell arrived on the ledge while Stewart was incubating. Through vocalizations, posture, and feather position, she gave him an invitation, and he responded. After a brief copulation, he flew off, and she took over incubation duties. It's not surprising that they would copulate occasionally during incubation; there usually aren't abrupt transitions from one behavior to another. This pair has been observed copulating in every month of the year; presumably the copulations outside the breeding season are pair-bonding behavior.
Incubation is proceeding steadily, day by day, one shift change at a time. On some days, Stewart does up to a third of the incubation; he has done over 40% in some years, but this appears to be at Bell's discretion. While the adults are taking turns on the nest box, looking sleepy, fidgety, or alert, the real activity is inside the eggs. We are over halfway through incubation now, so the embryos are becoming fixed within the shell as they move into position for hatching. During the first half of incubation, the embryos are more or less free-floating, and turning of the eggs by the adults keeps them from sticking to the inside of the shell; sticking would prevent their life support systems from forming. The heat that the adults transfer to the eggs via their incubation/brood patches is necessary for embryo development; all the turning and care that the adults provide would not do a thing if they did not warm the eggs.
The result of all this adult attention to those eggs should be tiny chicks. We expect hatching the first week in May - probably beginning mid-week.
