Although it has been over a decade, I still remember that morning vividly. I was observing the banded male and unbanded female on Brown Lake as they foraged on the wide portion of the lake’s eastern side. As is the case with most of our study animals, the loons were quite tame. They reacted indifferently to my red canoe as I tracked their progress slowly down the lake.

The loon pair’s relaxed foraging seemed odd during what had been a most tumultuous year on Brown. Though the female had resided on the lake since April, three different males had vied for and held the position of male breeder for portions of the season. Ultimately, “Mint-burgundy over Silver, Green over Blue-stripe” (Mb/S,G/Bs for short) drove off his competitors and became the male breeder. Evicted from Two Sisters-West in 2008, Mb/S,G/Bs had drifted about for two years before finally seizing control on Brown. Sadly, his victory in late June 2011 came too late for successful nesting to occur. So on the day of my visit, August 3rd, Mb/S,G/Bs and his mate were merely killing time before molting and readying themselves for the southward migration.

As I watched the laid back pair forage, an intruder appeared overhead. The pair watched the intruder as it slowed, descended, and parted the water’s surface to land twenty meters away. The intruder — a female hatched and reared 15 km north on Moon Lake, near St. Germain, three years earlier — was clearly uneasy. She bowed her head, dipped her bill in the water repeatedly as she drew near the pair, and initiated many brief dives as she circled them. For their part, the male and female breeder seemed to be going through the motions. They circled slowly with the intruder and peered at her when she dove but seldom dove themselves. The video below from South Two Lake depicts a similar scenario.

Afterwards I reflected upon the encounter. More clearly than ever before it seemed to me that I was watching a jittery youngster confronting two old, confident territorial loons. I am not sure why it had taken me eighteen years to do so, but I felt that I suddenly understood something very fundamental about loon territorial behavior. Loon pairs watch the behavior of an approaching intruder closely, quickly size it up — estimating the level of threat it poses to their territorial ownership — and then behave accordingly. As a result of this particular lake visit to Brown, my research team began to recognize and record “initiates dive” behavior (i.e. being the first loon in a group to make a short dive) and also “declines dive” behavior (refusing to dive when another loon nearby has done so). These advances led to new data collection and new insights into age-related territorial behavior.

Intruders, we have learned recently, provide ample signals of their age, fighting ability, and level of interest in battling for territory ownership. As the above figure shows, one of the clearest hallmarks of youth among intruders is the “initiates dive“ behavior. Young, timid intruders with no intention of vying for territory ownership are nervous Nellies, like this three year-old female was, and carry out many initiates dives. At the same time, these youngsters almost never show the “simultaneous dive“ behavior (which signals a willingness to escalate conflict), nor do they yodel or show aggression of any kind. Without question, there are dozens of other small signals that territorial pairs pick up from intruders to assess their age and degree of threat they pose.

And territory owners act upon the information they glean from intruders. That is, they treat a harmless visitor within indifference; they behave aggressively toward a dangerous intruder. The keen ability of territory owners to distinguish between intruders helps us understand how they can survive hundreds of intrusions each year without becoming exhausted. They save energy where they can and only get worked up and aggressive when they must.

These conclusions might sound obvious and intuitive. They are. And yet it took some 20 years and dozens of statistical tests to recognize and analyze the age-related patterns in behavior that allowed us to infer how both intruders and pair members betray their motives and strategies during such encounters. Fortunately, our perseverance has been rewarded. A few days ago our paper on interactions between intruders and territory owners was accepted for publication in a good behavioral journal. It should appear in print early next year. Thus, we are incrementally closer to understanding the entire territorial system of common loons.

If you would like to support our work in understanding territorial behavior, measuring population parameters, and conserving loons in the upper Midwest, consider a donation to the Loon Project HERE. At the moment, we are hoping to buy two canoes and a small motorboat, which would allow us to continue our long-term Wisconsin research while adding new lake coverage in our new Minnesota study area in 2022. Thanks for any support you can give us!

One of the challenges of behavioral research is to take notes that adequately describe the totality of what animals are doing. Since I am a behavioral ecologist, I devise a long list of behaviors that both appear important to the evolutionary fitness of loons and are also stereotyped or obvious enough for observers to record confidently on a datasheet. For example, when a loon bows its head so that its bill is pointing downwards instead of horizontally, we can all agree that it is exhibiting a “head bow”. When a territory owner slips quietly underwater, a nearby intruder flees across the water, and the owner resurfaces at the spot vacated by the panicked intruder, we recognize that the owner was “stalking” the intruder. We train field staff also to prioritize the recording of certain critical behaviors, like vocalizations, which reveal the motivational state of an animal and can be linked to particular stimuli occurring just beforehand (e.g. the flight of an intruding loon or eagle overhead). To aid new observers, we include a “cheat sheet”, shown below, that describes behaviors they are to look for and enter with our two-letter codes.

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Naturally, after 27 years of loon observation, we have seen or heard most of what loons can do. Indeed, we have analyzed many of these behaviors statistically to learn why loons carry them out. Yodels are a good example. By playing yodels back from loudspeakers to flying intruders, we were able to show that this call discourages many would-be intruders from landing on a lake and confronting the territorial pair. So a territorial male can employ a yodel as a means of defending his chicks from intruder attacks. Likewise, we have inferred that the mournful wail call must play a role in keeping pairs together and advertising for mates, because loons wail with great frequency: 1) when separated from their mates, and 2) when they lack a mate altogether.

But even two and a half decades of observation and statistical analysis of behavior is not enough to prepare us for everything loons do. This fact was brought home to me a few weeks back on Swamp. Following the death of the breeding female and departure of her former mate to Burrows Lake, an interesting new breeding pair had settled on Swamp. These new breeders fit the mold of many pairs we see: the female is a former breeder on tiny Prairie Lake but was evicted from there in 2015. She is at least fifteen years old and has reared six chicks to fledging. The male is a six-year old hatched on East Horsehead with no previous breeding experience. It is probably safe to say, after watching the video below, that he is still learning. To be clear, copulation in loons, when performed correctly, requires that male and female cloacas (genital openings) make firm and stable contact for several seconds so that sperm transfer can occur.

There are a few points to make here. First, though we might expect copulation, a very simple behavior pattern, to be largely instinctive, there are evidently some motor skills related to copulation (e.g. balancing on the female’s back) that benefit from learning. So males with no previous mating experience apparently fail in some early copulation attempts and must refine the behavior. Second, complex organisms show complex, non-robotic behavior patterns, especially when interacting with others of their species. Call it vertebrate bias if you like, but grasshoppers, crabs, and earthworms show a suite of behaviors that is relatively simple to catalog and describe. Loons, like squirrels and coyotes and turtles, sometimes carry out weird actions that don’t show up in the guidebook. So loon observers need to be ready to drop the two-letter behavior codes on occasion and just write down what the birds did.

Enough about science and field techniques. What I like most about this clip is that we can relate to it. If loons were humans, you could imagine the male saying, “Ok, wait….whoops….oh no…..whoa….oh gosh….umm….ok….nobody saw that, right?”


The deformity was obvious back on May 17th, when we first saw her. The breeding female on Johnson Lake had part of her bill jutting upwards at a crazy angle. At first, viewing her at a distance, we thought that the dark spike that appeared to emerge from her bill might be a lure of some kind that she had latched onto mistakenly and been unable to dislodge. But, as Elaina’s photo shows, the distal half of her bill is bent upwards at a 45 degree angle. We were alarmed at her situation, which appeared uncomfortable, at least, and deadly, at worst.

But she behaved normally. Since we carefully observe, painstakingly describe, and publish articles about loon behavior, we habitually assess any loon’s comportment that we see according to thousands of others seen before. Her diving and foraging was normal. Far from permitting too-close approach by humans — a common red flag that can indicate severe injury — she was actually rather skittish. She pointedly moved away from us whenever we approached in an effort to look for leg bands.

Anatomically, she is far from normal. Bird’s bills consist of a matrix of bony support, covered by a keratinized epidermal layer (rhamphotheca). In other words, the displaced part of this loon’s bill should comprise not merely soft tissue but bone. Mark Pokras, associate professor emeritus at Tufts School of Veterinary Medicine, assures me that the fact that the bony foundation that should extend to the bill tip is missing means that it “will never grow back normally”. The best we can hope for, he says, is that the bent keratinized tissue — all that remains of the end of her upper mandible — drops off eventually. I was chagrined to hear this news but heartened to learn also that Dr. Pokras has, during his decades of loon anatomical study, seen about 10 cases where large portions of loon bills have been missing. These cases include a male in Maine that had only half of an upper mandible (as this female does) but that fed itself normally, held its territory, and produced offspring in multiple years.

That loons can survive an injury of this kind to a crucial feeding organ and still breed seems remarkable. I suppose their resilience might be explained partly by the  challenges they face routinely across the range of different landscapes they inhabit. That is, an animal that must locate, pursue, and capture a broad spectrum of actively-swimming prey — in water that is sometimes fresh, sometimes salty; sometimes clear, sometimes turbid, must be a flexible and adaptable creature indeed.