Life on the Margins

For the past several years, I have begun to turn my attention to the effect of lake size on breeding success of common loons. Clearly loons on large lakes produce more and healthier chicks than those on small lakes. We showed that on our paper from six years ago. This raises the question of why loons ever attempt to breed on small lakes. They are doomed to failure — or at least to greatly reduced likelihood of success. The water is muddied further by the fact that loons reared on small lakes prefer to breed on small lakes themselves. That’s right: chicks fortunate enough to avoid starvation on small, food-limited lakes replay the whole scenario as adults, subjecting their young to the same travail they themselves faced.

The puzzle of loons breeding on small lakes was thrown into start relief again yesterday, when I visited the Wind Pudding-West territory on a scouting trip for nocturnal capture. After not finding the chick and parents in the shallow bay on the lake’s western side, where we had seen them on previous visits, I headed towards the channel that connects that bay with the main lake. I was crestfallen when I reached the channel, as it was choked with lily pads and grasses to the point where it was difficult for me to find a passage through — even in a canoe. This discovery led me to doubt whether the pair might lead their chick through the channel and into the main lake as a means of finding more food for it. I began to fear that — walled off from an abundant source of food — the chick had probably starved to death on the shallow western bay since our last visit.

I had underestimated the determination of the pair to provide for their chick. As I paddled to the end of the navigable portion of the channel, I heard a chick’s desperate cries to its parents. I spotted the chick about half way across the marshy isthmus that now separates the shallow western bay from the main lake. The isthmus is no more than 20 meters wide perhaps, but it is densely overgrown with marsh grass to the point where the chick — equipped only with legs at the very posterior of its body — was forced to lunge awkwardly forward in order to make headway towards the main lake. To make matters worse, the chick had no clear idea of where it was going. I caught the chick’s initial confusion on video, as it sits within the marsh grass, uncertain how to extricate itself.

The second installment shows the chick after it has blundered around in the grass for a time but finally gotten a sense of where its parent wants it to go. The chick stops to give a distress call, then hears its parent call to it, which seems to give the chick the strength to complete its journey. (Apologies for the nervous narration and grainy video!)

The fact that the parents can entice this year’s chick to cross the isthmus and take advantage of food in both the western bay and main lake means that they are better off than they were here in 2016, when a chick wasted away and finally died of starvation. However, we caught the chick and female in the video last night. They are both severely underweight. The female, in fact, has the lowest mass we have ever measured for an adult loon. So even if the pair can find enough food to fledge the chick, chick-rearing seems to have taken a toll on the parents. Add yet one more item to the growing list of reasons to avoid breeding on small lakes with limited food.