Understanding the Social Dynamics of Loon Territory Holders and Outsiders

By Natasha Bartolotta, Communications and Outreach Coordinator

Time seems to slow in those serene summer moments spent watching a pair of loons tend to their young. One can almost imagine the long life of a loon is made up of countless tranquil days like this on the lake waters.

A common loon adult on the lake’s surface with its chick by its side. Both are facing away from the camera, but the adult’s head is turned to the right, showing its side profile.
Photo by Brandi Grahl

In reality, there are many not-so-peaceful moments in the life of a loon. Common loons breeding on northern lakes are very territorial of their breeding grounds. They prefer to nest on quiet, protected shorelines and gain the knowledge of which specific locations are safe from predators by trial and error. It is the males who choose the nest locations and hold this valuable nesting site knowledge. Males will fiercely defend these territories from competitors looking to evict them, with territorial battles even becoming fatal. For young loons, it is a slow process before they can even begin to nest on a territory, with young males and females typically spending at least 2 years searching before settling on a territory. This creates an interesting social dynamic of loon territory holders and “floaters” a.k.a nonbreeding individuals that may compete with territory owners for a few years.

Two common loons face each other on a lake. The one on the left has its wings outstretched and neck craned forward.
Photo by Karen Field

For so long, the territorial dynamics of the common loon was a topic we could only speculate on. With dedicated behavioral research spanning decades, we have begun to know more. Using colored bands on loons to identify individuals has been invaluable to understanding the behavioral ecology of these birds. With each year, more and more loons in the population are banded, including these previously hard to track floaters. Countless mornings observing identifiable banded loons has led to new discoveries on the interactions between territory holders and outsiders.

The newest findings are summarized in a recent paper by National Loon Scientist, Dr. Walter Piper:

graph showing chick age (days) on the x-axis and number of yodels on the left y-axis (red line) and number of aggressive behaviors on the right y-axis (blue line). The red line for yodels peaks at chick age 0 then declines after that. The blue line for aggressive behaviors increases to peak around 15–20 days and generally declines after that.
Graph from Piper et al. 2022

By visiting territories, floaters learn if the location is a high quality nesting site via the presence of chicks. Floaters also sense the competitive abilities of the territory owners. As long-lived species, loons aim to acquire high quality territories for as long as possible. Interestingly, when an intruder lands on a territory, the defending loons can seemingly use the social behaviors of the intruders to assess what level of threat they pose. Only the male of a loon pair will yodel so perhaps this call can signal aggression among competing males.

As we enjoy our summer mornings along the lakeshore, we may hear the calling of loons echo across the water and be comforted by the sound. For the loons, however, this could be a sign of more treacherous waters ahead.

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National Loon Center

The National Loon Center restores and protects loon breeding habitats, enhances responsible recreation, and catalyzes critical loon and freshwater research.