Science is, by nature, cumulative. Theories put forward centuries, decades, or years ago form the foundation of ideas we test today. If those theories fail to explain patterns we see in nature, they are refined or discarded and replaced by new theories that themselves must be tested ceaselessly and revised or rejected.

For our part, we scientists spend years learning our field, which means achieving a deep understanding of the sweeping theories that have withstood the test of time. We also must have an intimate knowledge of recent findings of colleagues in the sub-discipline that forms the context of our own research.

The way that scientists carry out the scientific process should sound robust and logical. It is. This approach has led to steady progress in our understanding of the world and a guarantee that — although we may occasionally take a wrong turn in understanding some process or phenomenon — we shall not stray too far and for too long.

But the innate teamwork that typifies the scientific process has a major drawback. So desperate are scientists to keep up with discoveries and hypotheses of others in our own discipline that we expect to replicate their findings in our own work. Of course, such replication is vital to the scientific process; repeated similar findings confirm for scientists that we are seeing consistent patterns and have a solid understanding of nature. In our tendency to look for and find what others have found, though, we are often blind to what is novel. Indeed, if we discover some oddity, we are more likely than not to try to reconcile it with current theory by treating it as an aberration or an artifact of our procedures, rather than a truly new pattern that we do not yet understand.

So it was with spotlighting by loons. For years, I had observed the visits of territorial loons to their neighbors’ lakes. This behavior was curious, to be sure, but my training convinced me that these visits must have an explanation within the fabric already woven by other scientists. No, we would not expect territorial pairs with chicks ever to leave them at home and visit their neighbors with chicks. It made no sense. But until I took a long, hard, robust look at our data, I simply shrugged and trusted that someday we would be able to make sense of it based on what my scientific colleagues had found in other species.

On the other hand, all scientists are aware of this bit of wisdom familiar to fans of Sherlock Holmes:

When you have eliminated the impossible, whatever remains, however improbable, must be the truth. —Arthur Conan Doyle

Most ecologists encounter this situation seldom. It is, as you must imagine, a most unsettling outcome. However, in trying to test hypotheses to explain intrusions by loons with chicks into neighboring lakes, I encountered this situation exactly. Territorial loons, I thought, might be visiting their neighbor’s territories to look for food. That possibility did not stand up to scrutiny; intruders rarely forage during intrusions. Neighboring pair members, I reasoned, might intrude to learn about nearby territories, so that they would be positioned to “trade up” to a new one, given the opportunity. This possibility works for neighbors that failed to produce chicks, which sometimes trade up to the territory next door, but not for neighbors that hatched chicks themselves, which do not. Neighbors with chicks might intrude because — if they wish to draw attention away from their own chicks — they must go somewhere. This explanation fails because parents would be better off, in that case, visiting one of the many uninhabited lakes throughout the study area, where they could forage without interference from other loons and replenish their energy reserves. The fact that parents target other territories with chicks in precise, laser-like fashion rather than studiously avoiding them indicates that they are visiting specific territories with a specific goal. Thus, the improbable explanation that remains after all impossibilities fall away is spotlighting.

To conclude that loons are reciprocally spotlighting each other’s chicks is unsettling. No one has ever proposed such a convoluted mechanism of territory defense before. Our ability to develop the spotlighting hypothesis depended upon knowing loon behavior intimately. When you consider that: 1) nonbreeding floaters are obsessed with finding chicks to gauge territory quality for eviction attempts, 2) pairs with chicks are desperate to hide them from floaters, and 3) floaters are strongly attracted to other adults already intruding in a territory, it is not a great conceptual leap to suppose that adults eager to hide their own chicks would visit the neighbors to draw floaters to the neighbors’ territory and the neighbors’ chicks.

Since I am on a roll, I will add that the form of eavesdropping that loon pairs appear to do on each other’s yodels to keep track of each other’s breeding success is rather novel. That is, behavioral ecologists have long known the animals listen to each other and intercept each other’s messages in order to boost their own reproductive opportunities. Nightingales, for example, use their neighbors’ songs to determine where intruders are, so that they can defend their territories more effectively. But the kind of eavesdropping that I propose in loons — whereby loons use intercepted yodels to learn about neighbors’ chicks, spotlight neighbors’ chicks, and thus cause nonbreeders to evict neighbors — is far more sinister. The fact that eavesdroppers are causing harm to the loons whose yodels they intercept sets the loon system apart from other forms of eavesdropping that have been described in animals.

2009 video from Spider Lk, Oneida County.

I know. Web sites, books, “loon experts” — and our own hearts — tell us that loons are fundamentally good. Even when a pair with chicks hides them along a shoreline while confronting a raft of intruders, all of the attendees of the social gathering seem so respectful to each other, so congenial. But I am going to ask you to take the same sort of journey that I did as a scientist recently. Despite having been steeped for decades in narrow, Pollyannaish loon lore that holds that all loons are friends and are looking out for each other and the population as a whole, open your mind to the possibility that loons, like humans, do not always see eye to eye. Maybe, like me, you will find that this brings you closer to them.

If you have been reading my posts, you are aware that we now have good evidence for spotlighting of chicks. That is, our data suggest that: 1) parents of chicks systematically visit neighbors that also have chicks; 2) the added presence of these visitors draws in more young adult “floaters” to those neighboring lakes; 3) some of the floaters induced to visit neighboring lakes spot the neighboring chicks; and 4) these added chick detections by floaters result in increased attempts to evict the neighboring pair during the following year. Thus, adult loons with chicks draw the attention of local floaters to neighboring lakes and chicks and away from their own lake and chicks, decreasing the risk of losing their own territory to eviction.

Like most newly discovered behavioral processes, spotlighting alters the landscape and forces us to inspect some aspects of loon behavioral ecology more closely. Here is one puzzle raised by spotlighting: how do loons with chicks find out about the chicks of neighbors? Put another way, how does a breeding pair that is in the midst of protecting, feeding, and hiding their own young have time to spy on the neighbors so that they know where to spotlight? Remember that floaters, unlike established breeders, have no territories or chicks to defend, so they can spend weeks and weeks doing nothing but obsessively intruding into lakes to spot chicks and thus planning future eviction attempts. Territorial breeders with chicks, in contrast, must defend their territory, incubate eggs, and forage for and guard chicks. At best, they only have an hour here or there when they might leave their chicks behind and search for the chicks of others.

The answer probably has to do with territorial yodels. Yodels — like the one I recorded above on Muskellunge Lake (Lincoln Co.) in 2008 — are quite rare, and they occur mostly in a few narrow contexts. Specifically, yodels are frequent in all territories during the first few weeks after territory resettlement in the spring, are quite infrequent throughout incubation, and then suddenly spike again right at the time of hatching. This very precise, predictable pattern of territorial yodels thus conveys reliable breeding information to all loons (and knowledgeable humans) within acoustic range. Imagine, for a moment, that you are a territorial loon with close territorial neighbors both north and south of you. You hear: 1) an early burst of yodels from the north in late April and early May, 2) few or no yodels from the north for a four-week period, 3) a sudden burst of yodels from the north over a two-week period, and 4) occasional yodels for a few more weeks after that. This yodel pattern almost certainly indicates that a loon pair settled on the territory north of you, incubated their eggs for four weeks, hatched chicks, and reared them successfully for at least several weeks. Hence, this yodel profile from the north territory gives you vital information about the presence or absence of chicks without you ever having to leave the safety of your own territory. In fact, you might even be able to infer whether the north pair has two chicks or only one, because males defending two chicks yodel about three times as often as males defending a singleton chick! The fate of the breeding efforts of the pair to the south of you will also be evident acoustically. If you hear the same pattern of yodels to the south as you heard from the north, you know that the south pair too has a chick or chicks. And if the south pair yodels often only in April and May but seldom during the remainder of the summer, then they have failed to hatch chicks. When we look at the system closely, therefore, we realize that the fact that a breeding pair can collect a wealth of information about the neighbors without ever leaving their territory makes it much easier for them to detect the chicks of neighbors than it is for floaters (which intrude only occasionally) to do so.

In summary, the greatest puzzle regarding spotlighting — “How do breeding pairs know where to do it?” — is easily solved. Furthermore, scientists salivate at a behavioral system of this kind. Why? Because we can do a simple experiment to confirm it. Specifically, we can record yodels from Lake A, which is adjacent to Lake B, play Lake A yodels back to the pair with chicks on Lake B so as to simulate chick production on Lake A, and see if the Lake B pair intrudes into Lake A to spotlight the chicks there. If, as we surmise, pairs with chicks are spotlighting neighbors’ chicks, we should be able to induce a pair with chicks to intrude into a neighboring lake without chicks by playing yodels to them in a seasonal pattern that simulates settlement, incubation, and hatching of chicks by the pair next door!