Nest Duties

If you’ve been watching at the right time, you’ve seen a nest change and you realize that the male and female share nest duties. This video shows an early morning nest change, just before dawn, with the male relieving the female. This is typical of most loon pairs. Females tend to do the majority of night time nest sitting while the males patrol the territory for intruders.
There have been numerous published studies of loon nest duties and, all consolidated, it just shows that loons are individuals and they also adjust their behavior for local conditions. For example, on single-territory ponds (like this one), the loons tend to have longer periods of nest sitting than on lakes with numerous territories. All in all, they average around 3 or 4 hours between nest changes, but there is a wide variation.
Males tend to do more nest sitting in the early stages of incubation, presumably so the female can feed and replace all the nutrients she lost when laying eggs. Females tend to do more of the nest sitting during the second half of incubation.
When the sitting loon feels an urgent need to get off the nest, it will call to its mate by wailing. If that doesn’t work, it will go in search of the mate, leaving the nest unattended. Short periods of no incubation will not hurt the eggs. The major risk of leaving a nest unattended is vulnerability to egg predation.