Early yesterday morning, one egg was crushed while the female was on the nest. A while later, the male removed the broken egg from the nest. Crushed eggs during incubation is not that uncommon. It is a possibility we need to investigate any time we determine a nest failure cause.

So, what’s the deal? Are loons just naturally clumsy? Well yeah, they are, at least when they are out of the water. But there are other factors that can exacerbate the problem.

One factor is eggshell thickness. The legacy contaminate DDT is still in our lakes. DDT has a noticeable effect on loon eggshells, as it does on eagles and other species. Although loon eggshell thickness has slowly recovered from a minimum in the 1970s, it is still a little shy of the average thickness of pre-DDT eggshells.
And then there are neurotoxic contaminates that affect a loon’s behavior, mercury and lead being two of the most common found  in northeastern lakes. Loons can not only be a bit “loony”, some of them might also be “mad as a hatter”, or at least have compromised motor skills.
And in this case, judging by the egg contents that spilled out, we have an over-incubated, inviable egg that is subject to abnormal chemistry, gas expansion/contraction or hydrostatic pressure. It’s not surprising that it broke.