This is always the most asked question on the Loon Cam chat. Since we know exactly when the eggs were laid, we should know exactly when they will hatch. Right? Not necessarily; it isn’t that simple. Just as an expectant mother would be unwise to schedule, in advance, a hospital appointment for her due date, we would be taking a big chance to advise viewers when to tune in for the hatch.
If you peruse the literature and the web for the incubation period of common loons, you will find a smorgasbord of days or ranges of days for egg incubation. For instance, a 1980 study in Saskatchewan determined that the incubation period was 26 days. The New England Nature website currently claims that it is 29 days. This demonstrates an issue that all biologists are aware of: Any ecological study only describes what happened at the location of the study during the time period of the study. The value of the study is not so much predictive as it is comparative. It is comparing the differences between populations that help us understand how loons react to their environment. In the examples given above, the difference in incubation time might well be explained by the difference in body mass between the two populations. Northeastern loons are significantly larger than Saskatchewan loons.
There are numerous environmental, genetic and health factors that can affect incubation period. LPC has been collecting loon nesting data for 43 years now and we feel confident that the average incubation time for New Hampshire Loons has been about 28 days. You can reasonably expect any one egg to hatch within the range of 26 to 30 days. In this case, July 20 – 24. But outliers occur; don’t hold us to it.