Something feels different in northern Wisconsin this summer. Loon chicks are doing far better than in years past — and there are far more of them. Historically, chicks weighing over 3000 grams comprise only 1.4% of all chicks we capture. And we had not captured a chick of this size since 2017. Yet during the past five nights, we caught four such monsters on three different lakes. Gone too are the emaciated chicks from small lakes whose prominent skeletons cast doubt on their survival prospects. Last night, for example, we caught two fat, healthy chicks on tiny East Twin Lake. Their high and similar masses told us that their parents had not been forced into the usual Sophie’s Choice of favoring the older chick over the younger in feedings. Finally, there are more two-chick broods this year. At last count, 26 of 53 pairs with chicks in the Wisconsin Study Area still had two chicks, not just one. The robustness and abundance of loon chicks this year makes 2023 look like 1995.*
Two years ago, I would have scratched my head to see a sudden bounty of healthy chicks on lakes in Oneida, Vilas, and Lincoln counties. I have grown used to the demoralizing downward trajectory of loon reproduction in the area: 80% singleton broods, striking size asymmetry of two-chick broods on small lakes, and high chick mortality. Two years ago, I would have offered a few hypotheses to explain loons’ strange reversal of fortune in 2023. But I would not have understood it. However, we have been able to pinpoint specific environmental factors that affect body condition and survival of loon chicks.
How can we explain the abundance of fat, sassy chicks that we see in Wisconsin in 2023? In a word, drought. We now understand that the ability of loon parents to feed their chicks depends critically upon short-term water clarity. That is, water that is clear during the period of chick-feeding allows parents to find food for their chicks; murky water hinders chick provisioning. Furthermore, we have recently learned that heavy rainfall reduces water clarity — probably because rain washes lawn fertilizer, pet waste, and other human-related matter into lakes that supports phytoplankton growth. The low rainfall in northern Wisconsin during June and July 2023 exposed the region to a greater hazard of fires, but it kept lakes clear. That was great news for loon chicks and their parents.**
I am thrilled about the throwback year loon chicks are having in 2023. Each night I am dazzled by the size and vigor of the chicks we are marking. But since it has taken a substantial drought to produce chicks as healthy as those we saw routinely in the 1990s, the thriving chicks of 2023 also remind me how far we have fallen.
*The featured photo shows the 2023 field techs in Wisconsin holding the three strapping chicks from Kawaguesaga-North.
**Folks in Minnesota must be thinking, “Hey, we are in a drought too! What about our water clarity….what about our loon chicks?”. Our capture effort in the Minnesota Study Area occurred in mid-July. We marked dozens of new adults, but most chicks were small at that time. So we were not able to get good enough measures of older chicks in Minnesota to learn whether the drought gave loon parents a boost there, as in Wisconsin, by keeping lake water clear. However, we strongly suspect that the positive “drought effect” for chick feeding spanned the two states.