Finding Just the Right Territory

Pickiness is familiar to humans. We all invest considerable time and energy when looking for a home where we might live for a decade or more. But who knew that loons were equally choosy? Elaina and I have had a fresh reminder this past week of how finicky loons can be.

Sure, we have crunched the numbers. We know from the analysis that Mike Palmer and I ran six years ago that loons show a strong statistical preference for lakes that resemble their natal one in size and acidity. The figure above — though cropped for artistic effect — shows that both males (yellow arrows) and females (orange arrows) tend to settle on a breeding lake of similar size to their natal lake.

Knowing that loons eventually settle as breeders on lakes similar to their natal ones does not, unfortunately, tell us much about the exact means by which they choose a lake. That we must learn about by noting the sequence of lakes that a young loon visits, how long it stays on those lakes, and with whom it interacts while there. Although we have published a preliminary paper that dispels one popular idea about how loons might try to claim a first breeding territory and have long known that loons are strongly attracted to territories that are proven chick producers, we have quite a ways to go to nail the process down completely.

When we are out in our canoes, of course, we cannot see broad patterns. We simply note, for example, that a certain banded loner was at the north end of Birch Lake during the hour or so that we visited. At the end of each day, we check the database to learn the identity of any banded loon whose legs we saw clearly. Since we are tired, the discovery of a banded ABJ (“adult banded as juvenile”; i.e. a loon that we originally banded as a chick) that no one on the study has ever seen before elicits little more than a grunt of satisfaction. Then we ready ourselves for the next day in the field.

But the data accumulate. A loner that Elaina, Evelyn, and Tarryn saw yesterday at Katherine Lake, “Green over Green Stripe, Pink over Silver” matched a bird that I had encountered 24 days prior on East Horsehead Lake and that Elaina had seen on June 7th of last year on Bearskin. Three sightings do not constitute a publishable pattern, but this is a familiar observation on the project: a loon appears repeatedly on lakes of a certain size. The fact that we have seen this female only on large lakes (200 acres or more) and that she was also reared on a large lake (Two Sisters) suggests that she has a natal habitat preference for large lakes. What’s more, her apparent favoritism towards large water bodies at the tender young age of four indicates that she has already narrowed her choices, even though she will not settle to breed for two to three more years.

Our recent sightings of G/Gs,P/S — when combined with those of the 383 other young loons we have observed in the process of scouting out breeding territories — will help us piece together the strategy that young loons use to zero in on a breeding territory. If G/Gs,P/S is typical, young males and females cherry pick certain kinds of lakes to visit within their home region, skipping over many intervening lakes that do not catch their fancy. In another case, B/B,Ts/S, a male, was raised on tiny Fox Lake (15 acres), visited mainly small and medium-sized lakes when searching for a territory, and settled on Schlect Lake (25 acres). Since G/Gs,P/S and B/B,Ts/S have completely opposite ideas of what a good territory looks like, they could both inhabit the same cluster of 20-30 lakes during the two-to-three-year pre-settlement period, both search feverishly for a territory, and never meet.

We are nearing the point where we will formally analyze visitation patterns such as I have described to learn more about how loons decide on a breeding territory. Our data include sightings not only of adults but also of young juveniles in the late summer and fall after they have fledged but before their first fall migration. It seems quite possible that a rough picture of its ideal breeding lake forms very early on in the brain of a young loon.