At 3:56 pm yesterday, a full ten hours after nest abandonment, Dad returned and continued incubation. Mom took over a couple hours later and we’ve had constant incubation since then. So everything is copacetic, right?

Maybe. Ten hours is a long time for an egg to go without incubation. A lot depends on the weather during the time the egg was exposed. The good news is the temperatures were mild (afternoon maximum of low 80s) and there was very little direct sunlight before mid-afternoon (conditions ranged from fog to overcast to cloudy). So it’s unlikely the egg heated up to more than 100 degrees F. Normal incubation temperature is estimated to be in the mid to high 90s. However, the morning temperatures during the fog and overcast ranged from low to mid 60s for the first four hours of exposure. Minimum temperature and exposure time tolerances are not definitively known for loon eggs. We can’t be certain that the egg is still viable but we also think there could be a good chance that the egg could still hatch.

Some might argue that the first egg in a two egg clutch is sporadically incubated, sometimes left unattended as much as this egg was, and it will still hatch. But that’s not a fair comparison. A freshly laid egg has a fertilized embryo that can remain in suspended animation. An egg midway through the incubation process has numerous metabolic functions occurring that can be temporarily slowed down. But if metabolism stops, the the egg will be damaged.

Folks have asked if going 10 hours without an egg turn could hurt viability. Again, we don’t have any definitive data for loons but other species that have been studied show that egg turning twice a day is adequate for proper development. This shouldn’t be an issue.

Like all else in nest sitting, all we can do is wait and see. If the egg hatches, we’ll have an interesting data point for our understanding of incubation. If the egg doesn’t hatch, all we can do is scratch our heads and wonder.