June 1, 2021
Loon watchers who follow the Chat on YouTube may have seen references to “forks”. It’s a means of using the loon’s necklace to differentiate between the male and female when the bands are not visible. The necklace consists of two rows of vertical white pinstripes, one on each side of the loon’s neck (or you could describe it as a ring with gaps in front and back). Most of the pinstripes are simple, straight lines but there are usually one or more pinstripes that diverge into a “Y” shape, which can either be right-side up (fork up) or up-side down (fork down). In the case of this pair, it’s been reported that, on the right-hand side, the female has two forks up and the male has one fork down.
During my first year at LPC as a neophyte loon biologist, I noticed this variation in necklace patterns and I suggested to a wise and venerable veteran of loon biology that it could be used as a unique identifier, just as oceanographers use the color patterns on whale tails. I was flatly informed that it wasn’t reliable; necklace patterns could change during preening or molting. That was fourteen years ago. In the interim, I’ve learned that my observations were certainly not unique and there has been much discussion about necklace patterns. Although I haven’t found any published studies on the common loon, a group in Finland did a study on variations in the neck patterns of arctic loons. They found that the patterns remained constant between years but use as a unique identifier was successful only 70% of the time in a population of 127 loons.
There is no doubt that loon watchers on YouTube or residents on loon lakes can use physical characteristics to distinguish between individuals. But when you are following 750 loons and covering 382 lakes, identifying loons by neck patterns becomes awkward and unreliable. We also have to deal with the simple fact that, for most of it’s life, a loon is not in breeding plumage and it has no necklace. Juvenile plumage lasts for the first three years and adults are either in or transitioning into or out of winter plumage from late September through March.
LPC and all other loon study groups rely solely on colored bands for identifying individuals. It’s a simple system to learn and it remains reliable throughout the entire life of the loon. But by all means, use physical (and behavioral) differences for keeping track of your favorite group of loons. It’s a great way to better know these fascinating birds.