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In a sense, our ability to identify loons as individuals hangs by a thread. As most of you know, we rely upon a unique combination of three colored leg bands — together with the mandatory numbered USGS metal band — to ID our study animals. The Upper Kaubashine female, for example, is “silver over yellow on right leg, red over green on left leg”, while the Lee Lake male is “blue with white stripe over taupe with white stripe on right, red with white stripe over silver on left”. (He is nicknamed “Stripe Hell” by my staff.)

The system seems simple enough on its face. Together with the DNR, however, we have banded over four thousand adults and chicks in northern Wisconsin since 1991. Thus, we have used a lot of color combinations over that span. Inevitably, certain individuals differ only slightly from other individuals in their band combination. While we make every effort to use contrasting band combos on mated pairs, loons move around between lakes because of natal dispersal (movement from natal lake to breeding lake) and eviction. Sometimes birds with similar band combos end up close together. For instance, the male on the southeastern end of Squash Lake, which we caught last night, is “yellow over taupe stripe, green over silver”, while the female at the northwest end of the same lake is “red over taupe stripe, green over silver”. A single band is crucial to distinguishing one bird from the other on Squash.

I describe our identification system as fragile, because the loss of only one of its four bands by a loon can throw its identity into question. In several cases, a loon with one or more missing bands could only be ID’d when it was captured and we read the number on its USGS metal band. In most years, there is at least one such “mystery loon” in our study area.

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Our mystery loon of late has been the female on Bear Lake (pictured above in Linda’s photo). She has lost one band and is now “orange over mint burgundy, silver only”. A check of our banding records finds four birds that could match that combo, if they lost a single band. All are “ABJs”: adults banded as juveniles. In other words, all were marked as chicks: one in 2004, one in 2005, and two in 2007. I was excited to see that Bear Lake had a chick this year, because this gave us a reasonable chance of being able to capture Mystery Female and learning her age and natal origin from her metal band. But she is a skittish bird, and we failed to catch her.

So we left it to Linda. Linda is a great photographer and a very patient naturalist. Many times she has taken photos so crisp that one can read the numbers stamped into the metal band on birds legs. Below is an example of a photo by Linda in which one can make out several numbers on the metal band on the right leg, above the “auric with red stripe” band. I thought that Linda might pull off the same magic with

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the Mystery Female, which would permit us to discover her age and natal lake. Thus far, she has been able to make out three separate digits on the bird’s metal band. That information has allowed us to eliminate two of four possibilities; we now know that the Mystery Female was hatched on either North Nokomis Lake in 2005 or on Buck Lake in the same year. The tendency of young adults to settle on breeding lakes similar in size to their natal lakes makes us favor North Nokomis as the more likely natal lake. If we are lucky, Linda might get a chance to nail the numbers well enough for a certain ID.

Now you might wonder why we are so obsessed with the identity of a single loon. After all, we have identified scores of other lake settlers who held onto all four of their bands. We have come to feel that each data point is precious, because each one allows us to refine our population models and survival estimates. Females are particularly valuable to us, because most of them disperse so far from their natal lake that we cannot relocate them as breeders. (Males, in contrast, often settle within a few kilometers of their natal lake, so we have far more data on male settlement.) So please send positive vibes Linda’s way, as she hunts the skittish Mystery Female of Bear Lake.