The beginning of the tale is heart-rending. A gosling is orphaned before hatching. A loon pair fails to hatch chicks of their own and, seeking to fill the void, sits on eggs they find near their nest. When these two desperate parties converge into a single — if nontraditional — family, they produce a heart-warming story*.

To see two species coexist despite 90 million years of evolutionary time spent apart is surprising. To see them not merely tolerate each other but become thoroughly interdependent, as parent and offspring, is truly striking. Such an improbable scenario makes one hopeful. This story suggests that differences between groups — even vast ones such as between geese and loons — can be overcome.

On the other hand, the sight of a gosling nestled comfortably on a loon’s back is also strange. It is a reminder — like exploding black fly populations, loss of water clarity, devastating storms, and the sudden abundance of wake boats — that the loon’s world has changed.

*Thanks to photographer Brad Thompson, who shared his beautiful photo.

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I love the painting because it is not about loons. John Seerey-Lester’s artwork*, pictured above, is about rain. The painting recalls those moments when you were out on a lake — taking in the vast expanse of its surface; gazing at an eagle circling high above; or watching a loon pair drift by with their four-day-old chick — and a rogue cloud emptied upon you. Most of us who have ventured out onto lakes can recall such an experience. In the moment, there is panic: a hastily zipped jacket, a vain attempt to find some form of shelter to thwart the impending deluge. But there is wonder and beauty in the storm itself. As Seerey-Lester’s painting shows, raindrops transform a lake’s monotonous surface into an astonishing palette of dancing splashes. Accompanied by a soothing whisper, the spectacle of a rainstorm on a north-country lake is one of nature’s wonders.

Loons cope well with rain, of course. What harm is more water, after all, when you live in water? Like most birds, loons assiduously preen their feathers, coating them with oil from a gland at the base of their tail, so water beads up on their heads and backs, but ultimately rolls harmlessly off them — like water off a loon’s back. A downpour might necessitate a few shakes of the head, inspire a few extra wing flaps, and prevent foraging for a time, owing to reduced visibility. But loons greet rainstorms with little more than a shrug.

Considering the grace with which rain appears in loons’ lakes — and, of course, its fundamental importance in supporting all life — I was unpleasantly surprised to learn this week that rainfall has likely contributed to the reproductive decline of loons in northern Wisconsin. You see, rain does not merely stimulate plant growth, raise water levels, and rinse car windows. Rainfall also washes all sorts of matter into lakes. This includes visible organic matter such as sticks, leaves, and soil but also invisible nutrients and chemicals. Many substances that reach lakes via rainstorms reside naturally in soils or on the forest floor. Others, like fertilizers and sewage, have been added by humans to the environment. Human-added materials that contribute nitrogen and phosphorous to lakes can cause populations of phytoplankton to surge, which reduces water clarity.

And this brings us back to loons. Loons rely strongly upon their vision to catch fish and other prey underwater. As our recent investigations have shown, reduced water clarity hinders loon foraging. We now know that reduced water clarity leads to poorer body condition both in breeding males with chicks and in chicks themselves. The decline in chick body condition and accompanying rise in chick mortality are essential components of the breeding decline now underway in northern Wisconsin.

Water clarity in loon breeding lakes in July declines with increased rainfall in June and July.

Why am I so determined to blame it on the rain? Because a few days ago I examined water clarity estimates from my collaborators — Kevin Rose and Max Glines of Rensselaer Polytechnic Institute — and found that water clarity in July, the best predictor of adult male and chick mass, is, in turn, strongly dependent the amount of rainfall in June and July. Just as April showers bring May flowers, June and July showers bring July algal blooms in Wisconsin lakes that make it more difficult for loons to find their prey.

Of course, rain itself is not the true villain. Rather it seems to be fertilizers, leaky septic tanks, and maybe even pet waste that human lake residents have added to the ecosystem that are contributing to the loss in lake clarity.

You might wonder if there is truly a sustained, irreversible downward trend in water clarity or whether water clarity fluctuates according to natural cycles and is merely on a downward trend at the moment. If we are simply on a temporary downward trend, then it is a decade-long trend, according to Max and Kevin’s measures of water clarity (see graph just below).

Moreover, as I reported recently (see graph below), loon males have been losing body mass for the past 30 years. So the data we currently have indicates that we are on a prolonged downward slide with respect to both water clarity and loon mass.

Male loons have been gradually losing body mass for the past 30 years; female loons do not show such a decline.

So what do we do? All hope is not lost, I think. But if our data and interpretation are correct, then we must immediately begin to monitor — and curb — chemical runoff from shorelines into lakes from sources such as fertilizers and septic systems. In the long-term, we need to understand that summer rainfall will only increase as the Earth continues to warm and cloud formation accelerates. In short, it is a bit harsh to blame the rain for loons’ current reproductive woes, but increasing rainfall in coming decades will probably push us more rapidly in the wrong direction.

*”Sudden Rain”, copyrighted by Sir John Seerey-Lester