How Bad Was 2020 for Loon Chicks?

I feared in May that 2020 would be a forgettable year for breeding among loons in northern Wisconsin. As many followers of the blog may recall, I wrote numerous posts this spring and summer warning of reproductive struggles of loons in Oneida, Lincoln, and Vilas counties. Before I was even able to visit my study lakes in late May, the die was cast. Black flies, Linda told me in early May, were worse in 2020 than any year during the 28-year study — worse even than in 2014, when about 80% of all first nests were wiped out by the relentless blood-suckers. Indeed, only 3 breeding pairs out of the 109 that we followed this year were able to incubate to hatching a nest that they began in May. The flies were a painful punch to the gut from which the breeding population never recovered.

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Despite the huge setback caused by the flies, most pairs forced to abandon their first nesting attempt renested in June. Many such pairs used promising nest locations on islands, protected boggy shorelines, or marshy mounds formed from emergent vegetation; still others placed their eggs of artificial nesting platforms anchored on lakes by lake residents anxious to boost their efforts. And so, in spite of the challenges, many nesting pairs hatched late chicks. These successful pairs included several on lakes that had not produced chicks in many years, such as Hodstradt, Shepard, and Dorothy. They included a few lakes where entirely new breeding pairs had settled, found good nesting places, and hatched young, like South Two, Silver, and Miller. Finally, one breeding pair — on Baker — performed the most impressive feat of all, raising their own loon chick in 2020 after having reared a mallard duckling to fledging in 2019.

Yet all of these heart-warming breakthroughs combined were not enough to lift the breeding rate this year to respectability. As the graph shows very clearly, 2020 continued the steady decline in the reproductive fortunes of northern Wisconsin loons that began over two decades ago. The decline is marked not only by increased black fly harassment but by increased losses of chicks after hatching — both young and old chicks.  Altogether 9 of our pairs patiently sat on their eggs for 4 long weeks only to lose chicks in their first week of life. An additional 8 pairs reared chicks past the “danger period” of the first two weeks but lost one or both chicks later (and a few more, perhaps, will be lost in the coming weeks). In short, we can no longer breathe a sigh of relief after chicks hatch — or even after they reach 2, 3, or 4 weeks. As a matter of fact, I no longer know at what age we should count chicks as having survived. Mortality of chicks of all ages is much higher now than in the 1990s or early 2000s. Statistically, 31% more young loon chicks (<2 weeks) die now than before, and the death rate of old chicks (>5 weeks) has increased by a staggering 81% in the past 28 years.

After having blithely focused my attention on the territorial behavior of loons for a quarter century, I am now compelled to look at what is causing the sharply higher mortality among chicks and young adults. I feel as though I owe it to the folks who live on the lakes of the Northwoods and imagined that they would always hear the sounds of loon calls echo across the water. And I owe it to the loons themselves.