Ruminations on Spotlighting

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!