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.

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.

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 loon biologist, Dr. Walter Piper:

1. As these nonbreeding “floaters” got older they became more likely to intrude on territories of pairs that had chicks the previous year, less likely to be submissive to the territory owners, and more likely to be aggressive or yodel (note, it is only male loons that yodel).
2. Compared to neighboring loons of territory holders, floaters were more likely to intrude on the territories and will remain for a longer period of time. Floaters were also less likely than the neighboring loons to intrude on territories with chicks.
3. When floaters intruded on lakes that were home to hatched chicks the year before, the social interactions of floaters increased.
4. Territory owners were not any more aggressive to floaters than they were neighbors, but they did behave aggressively towards older floaters. Older floaters are more dangerous, because they have the size and fighting ability to challenge owners in battle and evict them.
5. Territory owners were particularly defensive when chicks are small. Males with young chicks seemed to yodel to discourage intrusions and relied on more aggressive tactics to defend chicks once they are older.

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.