Who Likes Record-High Water Levels? Loons on Hodstradt and Dorothy!

Most scientific research comprises snapshots of a biological system. That is, we usually study the behavior or ecology of an animal for a year or two in a forest, on a coral reef, or in a desert. On the basis of such a short term study, we pontificate about what constitutes a good territory and what constitutes a bad territory for the animal we are studying. Then, feeling that we have described the system accurately, we fold our tents and move on to the next study and habitat.

But time changes things. My team and I got a demonstration of the impact that time can have yesterday when we visited two lakes located towards the northern part of our study area. Life has always been hard for loons on Dorothy and Hodstradt lakes. They are both rather clear lakes and full of fish. But they have been disasters reproductively, because they lack the islands, marsh, and bog that loons seek out to keep their eggs safe from raccoons.

The gradual but now-dramatic rising of lake levels in the Northwoods has produced a spectacular reversal of fortune for loons on Dorothy and Hodstradt. What had been an unremarkable spit of land on Dorothy has become an island several meters offshore, reachable only by water (see photo below). What once was a long curving peninsula on Hodstradt has been transformed into an island, accessible only after a lengthy swim. In short, two lakes for which chick production was a freak occurrence have now become prime real estate, because they offer offshore nest sites inaccessible to all but the most ambitious raccoon.

Of course, the rising waters have not been kind to all lakes. Heiress Lake had a handy island that saw regular chick hatches in the late nineties and early 2000s. But no more. That raccoon-proof site is now four feet underwater, and Heiress no longer supports a breeding pair.

The take-home message is clear: territory quality is not fixed and unchanging. Instead, changing climatic patterns transform the landscape in surprising ways. A goldfinch’s lifespan is short enough that habitat transformations probably matter little. But loons live long enough to see poor nesting habitat become good nesting habitat and vice-versa; this species should be able to detect and respond adaptively to fluctuations in territory quality.

In fact, loons do exhibit some ability to respond to changing landscapes. We see this ability in the willingness of breeding pairs to explore vacant lakes near their original one and sometimes nest at sites different from those they have used to hatch chicks. And, of course, young nonbreeders use the presence of chicks on a territory as a measure of current reproductive quality so that they can target lakes for eviction attempts that will reward them with many offspring. On the other hand, many adults settle on a productive territory during the prime of their lives only to see its quality decline along with their own body condition. Lacking the fitness to defeat an opponent in a battle for a new territory, such birds are stuck breeding on a failing territory. These old codgers could tell ecologists a few things about territory quality and the passage of time.