Has Chick Growth Slowed in Recent Years?

The Audubon report put me on notice. Loons are not immune from climate change. While I have wondered at times whether their aquatic habitat might somehow buffer them from the warming of the Earth and increased moisture in the atmosphere, this was a false musing. Recent changes in temperature and precipitation have myriad and complex effects on lakes and their inhabitants. Loons will have to confront the changing conditions just like all other organisms must.

I wondered whether my long-term data on loons might show climate-induced changes. I am not a climate scientist — nor even a hard-core ecologist who might routinely measure fish populations, water temperatures, or lake chemistry. But we do weigh all loons that we capture and band. Perhaps masses of adult loons or chicks have fluctuated in response to the changing climate.

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My findings are quite striking. Chicks have decreased in mass consistently since my team began capturing and marking loons. This finding alone is worthy of concern, but it is not the only one. Breeding males (see below) too show a decline in mass during our study. Breeding females, on the other hand, show no steady loss in mass.

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What are we to make of these patterns? Are populations of small fish down in the past few decades such that chicks and their male parents struggle to put on or maintain body mass? Or are lakes changing in ways (e.g. clarity) that might make fish more difficult to catch? Whatever the cause of these decreases in mass, why are female loons not affected similarly? These questions must remain unanswered for the time being. In fact, these results are so new that I must run some more double-checks before I fully trust them. Even if they are real effects, as it appears, it is much too early to attribute them to global warming. My worrying self, though, fears that these significant declines in body condition might be the leading edge of a changing climate’s impacts on Wisconsin loons.