Sticking to a Nest

We’re now at 31 full days of incubation, and the chances that the single egg will hatch are low. Loons sometimes stick with a nest, or overincubate, long after the egg should have hatched. Most inviable eggs are abandoned in the first week after expected hatch, but some loon pairs overincubate for a month more.  A new record of 84 total days on the nest–eight weeks past the expected hatch date—was set last year by a pair on Squam Lake.

Eggs that don’t hatch may have been inviable from the start, or may have been chilled, overheated, or otherwise compromised during incubation. Loon Preservation Committee field biologists collect confirmed inviable eggs for analysis and archiving, following a protocol under state and federal permits.  On average, about 10% of successful nests, where at least one egg hatches, yield a whole, unhatched second egg.  This gives some indication of how often eggs are inviable from the start, since we know the conditions were adequate for the second, successful egg in these nests.   Infertility, and failure of a fertilized egg to develop, may be influenced by the health and contaminant burden of the loon pair as the egg is formed, as well as the host of factors that can inhibit development once the egg is laid.  Protecting loons means understanding and preventing these factors where that can done.  But even when some factors, like environmental mercury, are clear problems in general, it’s usually impossible to pinpoint a single cause at particular nests.  So the unhatched egg we’re watching so closely on the webcam will likely remain an unsolved mystery.   We are rooting for these loons to move on soon to a second nest attempt, with better luck.  And remembering that the loons are in it for the long haul—this female loon has fledged nine chicks since she was originally banded in the late 1990s, already enough to assure her legacy in the gene pool.