May 22, 2022
Choosing a territory is one of the most important decisions a loon needs to make. The “perfect” territory will have good water clarity, plenty of prey for both adults and chicks, is easily defensible from other loons, and has at least one good nest site.
In choosing a nest site, the loons are looking for a spot that is protected from terrestrial predators as well as wind and wave action. The more foliage the better, because it helps hide the nest from avian predators and nosy humans. The location that best fits the bill is the lee side of a tiny island in a sheltered cove. But there are not enough tiny islands in sheltered coves to accommodate all the loon pairs so they have to make do with what is available.
But who makes the choice? If you have the good fortune to watch a pair of loons nest site shopping in the spring, the soft vocalizations and head bobbing make it appear that it is a joint decision, made only after a long discussion and agreement between the two. But Walter Piper, a friend and colleague of LPC, has another idea. Walter reviewed the records of mate swaps and nest location changes on numerous loon territories in Wisconsin and found that nest site locations change much more frequently when there was a new male as opposed to a new female. (This is a bit of a simplification. Walter’s study was looking at the “win—stay, lose—switch rule”, but that’s a whole ‘nuther blog.) This is strong evidence that males choose the nest site. What it means for the loons is that it’s to the male’s advantage to keep a territory with which he is familiar; it’s to the female’s advantage to get on a territory that’s been held by one male for a long time.
And who chooses when to start nesting? This is a little more complicated. Sometimes it may not be the pair that makes the choice. If there is interference from other loons the pair may have to forego nesting until they can secure their territory. But when the territory is secure and the nest site is chosen, it’s up to the female; if not rationally, at least physiologically. One thing we know for sure, isotope analysis has shown that the eggshell and contents are from the lake, and not from the ocean, where the loon was before flying to the lake. So the female has to consume enough nutrients to replenish what was spent during the migration, to maintain good health, and then to produce two large eggs – about two thirds of a pound. Any nest initiation in May is earlier than average, which in New Hampshire is around the first week in June. This pair are pretty reliable late May nesters so we are expecting them to be on the nest any day now.