June 15, 2023
Our Cam 2 pair deposited their second egg in the nest yesterday morning, exactly 62 hours and 30 minutes after the first egg was laid. Going by the general rule of thumb I learned when I was first introduced to the natural history of loons (2 eggs one or two days apart), we might think this was an abnormally long time between appearances but loon cam records over the past seven years show otherwise.
Of the nine nests where we are sure of the dates and times for both eggs (+/- an hour or so) we get an average of about 61 hours between eggs and a range of 58¼ to 63½. If we make subsets of the three females we’ve been following over this period, their individual time ranges are even smaller. Female #1 (the old Cam 1) had a range of 58¼ to 59½. Female #2 (Cam 2) has range of 61 to 63½. Female #3 (the current Cam 1) has two clutches so far, both had 62¼ hours between eggs. I feel comfortable in saying that our New Hampshire loons lay eggs about two and a half days apart.
So where did this “one to two days apart” thing come from? Well, for starters, we’ve never had 24/7 observation coverage until the loon cams became a thing. Prior to that, the best any nest had was a daily visit. Biologists covering numerous small lakes scattered over a region of the state would be doing fantastic work just to get weekly visits. The one data point we had to get was the OTN (on the nest) date. More often than not, that was “calculated”: the date half-way between two inspection dates. Determining the time between eggs was a practical impossibility..
The other issue is that the first egg is usually only sporadically incubated. A biologist might pass by the nest and not see a loon sitting on it, and just move on, not realizing that there was an egg in the bottom of the nest. Many recorded OTN dates are likely to be a day or two after the first egg was laid. And then after all that, the eggs hatch about a day apart. Logical reasoning based on low-accuracy data would result in an estimate of one or two days between eggs being laid.
This is just one of the revelations the loon cams have provided us. They will continue to give us more insights into the lives of breeding loons.