[LOON CALLS] CHARLES WALCOTT: If you have ever spent time on lakes in the northern United States and Canada, I'm sure you are familiar with the common loon. Here, a pair quietly interacts.
And here, in the early morning mists, a pair produces the characteristic tremolo, or laughing call.
[LOON TREMOLO CALLS]
But all is not peaceful in the world of loons. These two females are fighting over a territory.
Why do loons fight? And why is a territory so important to a loon? My colleagues and I have been studying a population of banded loons for the past 18 years, and we have begun to find the answers to some of these questions.
In the normal course of events, one loon looks very much like another loon. And it was the work of David Evers, now of Biodiversity, who figured out how to catch loons and put bands on them. And Professor Walter Piper, my colleague, will show you how that's done.
WALTER PIPER: It's tense to find them--
STUDENT 1: OK.
WALTER PIPER: --once they start diving. That's tricky and testy. But [INAUDIBLE] find is to not get things--
STUDENT 2: Whoa, that's great.
WALTER PIPER: I have another thing that's a spotlighter.
STUDENT 2: [INAUDIBLE]
WALTER PIPER: [WHISTLING]
The battery is dying. The motor is dipping. Silver over mint, silver over mint. White over taupe stripe.
STUDENT 2: White over taupe stripe.
WALTER PIPER: When you mark and can individually recognize an animal, especially an animal like loons, like the loon in which all individuals are identical, you've really got a leg up on the system.
And if you can consistently-- if you can mark individuals and then consistently find and see all of the markers that you put on them to recognize who you've actually got there day after day after day so that if anything-- you have any departure from that, like that bird being displaced from its territory, you can pick that up, that gives you a real window into the system that doesn't otherwise exist.
But the real driving force of the study is our desire to learn about territorial behavior, to use the loons to learn, ask questions about territorial behavior that are hard to address in other systems, because we can mark the loons, because they're long-lived. And once marked, they tend to remain so because they're faithful to their territories.
Do they mate for life? And this legend has grown about loons over the years. And of course, it could grow-- it makes sense that it can grow because until you band and kind of individually identify loons, all of them look more or less alike.
It's very difficult to tell one loon from another. Males are larger than females, but otherwise, it's very difficult to tell them apart. And so the people who come up to their lake, they see a pair of loons that look just like loons from last year, and they say, well, the loons are back.
And the answer-- and loons don't mate for life. There are takeovers that occur, and both males and females are liable to lose their breeding slot to a male-- could lose it to another male who comes in and displaces it from the territory, sometimes fatally. Females also get displaced commonly from their territories.
And so they don't mate for life. They seem to practice the strategy that if you can't be with the one you love, love the one you're with. It's a little bit of a rough way of stating it. But loons seem to have an allegiance to their territory that's very strong, and they'll remain on that territory, in most cases, for many years. But they don't have a strong allegiance to their mate. When their mate gets displaced from a territory, the loon will pair with the usurper of the pair.
And so one of the hypotheses is that males become senile. And our evidence for that is that males do tend to lose mass over time on their territories, whereas females do not. And so that is consistent with the idea that perhaps males are becoming less-- are declining in their condition to a point, perhaps, where they become easy prey for a large, fit, aggressive intruder.
Another part of the story, inevitably I'm sure, is that males and females have an interesting contrast in their nesting behavior, their contributions to nesting behavior. This is something that no other study has found to our knowledge.
Males and females both look for nests together. And to observe them, it looks like both males and females are interested in finding the best nest location. But if you look at it closely and you look at the data, what you find is that it's males that are the ones that are looking for the nest. They're the ones that are positioning the nests.
Male loons have a very simple rule, as do many species of animals. And that rule is-- it's called the win-stay, lose-switch rule. And it just means if you've succeeded in producing chicks or produce young at a certain breeding site, we use that site. Very common sense rule of thumb that many animals employ. And so males-- so we know that breeding pairs-- years ago, we would have said, well, breeding pairs obviously use the win-stay, lose-switch rule.
But we've accumulated enough data on marked pairs, and we have enough cases where one or the other member of a pair has been displaced so that we can look and see, well, what happens if a pair produces chicks from this nest site, and then the male gets displaced and the next year it's a new male and an old female? Do they use-- do they still continue to use the rule?
And to make a long story short, when the male turns over the pair suddenly stops using the rule altogether. Even though the old female is there and potentially possesses the information about where to nest, that information doesn't make it to the next nesting attempt.
Being that old female has been on the territory for a dozen years is completely at the mercy of her ignorant new mate when he comes in, and she just has to nest wherever he decides to nest [AUDIO OUT] attempt.
On the other hand, if you have a female displaced on a territory and a new female come in with the old male, that pair continues to act just like a pair that's completely unchanged from the previous year. That is, they continue to use the rule.
Loons are long-lived organisms. Now that we've started to mark a large number of them, we're realizing, somewhat to our chagrin, how long-lived they are. Just hoping to outlive some of my study animals. And so considering that these birds live 25 or 30 years, it means that an average loon will have to deal with breeding on at least two or three or four or perhaps more different territories during its lifetime.
Since we started to mark many chicks, beginning in 1998 and essentially saturation banding of all the chicks that are produced in our territory beginning in 1998 and it's now 2008, it's been 10 years since we've started that process. And we've had well over 100 of these young birds-- we call them ABJs, Adults Banded as Juveniles, that's our little terminology-- we've gotten a lot of ABJs coming back-- birds coming back to the near vicinity of where they were banded three or four or five years before.
And so that allows us-- gives us really a unique window into the process of territory acquisition by young animals. Very few studies have enough animals marked as young individuals who are looking for territories to be able to say, ah, this animal was hatched here four years ago.
It's setting up a-- it's visiting, intruding in these territories in this particular area. It's living on this big lake over here, and it ultimately evicts a male or usurps the territory from this male in this territory. And so it's giving us a great deal of exciting information.
CHARLES WALCOTT: Loons have a number of different vocalizations. And I've asked John Mager, a professor at Ohio Northern University, to tell you a little bit about the sounds they make and what we believe to be the meaning of those sounds.
JOHN MAGER: Loons characteristically give three vocalizations that are able to be communicated over long distance. The first is a wail, which is the haunting call of the loon, the laugh-like tremolo, and the yodel. The wail has been long believed to be a contact call. It is a call that's often given by mates to find one another or perhaps mates looking for misplaced chicks.
[LOON WAIL CALLS]
The tremolos are basically when loons are agitated. So it's believed to be a signal given when they're threatened.
[LOON TREMOLO CALLS]
Whereas the yodel tends to be a call-- it tends to be territorial in nature and that it's only given by males. And it's usually given in the context of when an intruder has flown into or is flying over the territory.
[LOON YODEL CALLS]
As being communicated by the yodel are three things. First of all, what I think the yodel is communicating is something about the identity of the individual male giving the yodel. That is, it's indicating that I am Bob or I am Ted or I am the resident loon in this particular territory.
I also believe that the yodel is communicating something about the relative fighting ability or strength of the bird, that is, how big the individual is, and therefore, what type of a physical struggle that an intruder might be looking at as a potential threat.
Lastly, I think the yodel is also communicating something about the aggressive motivation or willingness to defend that territory, that is, how agitated they are and how willing they are to try to displace any type of intruder.
CHARLES WALCOTT: That each individual male loon has his own characteristic yodel. The surprise, however, is that when a male is displaced or takes over another territory, it changes its yodel. And it doesn't just change it at random. It changes it to be as different as possible from that of the previous male on the territory. For some reason, it seems to be very important for the loon to say, new loon on the block, as it were.
So now the next time you see loons on a lake or listen to their haunting cries in the early morning mist, you can appreciate what an interesting and complex social system they have and how much we have been able to learn by studying marked individuals.
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Common loons defend breeding territories on fresh water lakes in the northern US and Canada. While a great deal is known in general about their breeding biology it was the advent of banding that enabled identification of individual loons.
Cornell professor of neurobiology and behavior Charles Walcott and colleagues Walter Piper and Jay Mager have been studying a banded population of loons near Rhinelander, WI for the past 18 years. They have found that loons are quite faithful to the lakes on which they breed returning for an average of 5 years. Loons looking for a breeding site will either pick a vacant lake, replace a missing breeder or actively displace a pair member.
Female fights are relatively benign with the winner taking over the territory and the resident male, the loser moving to another lake in the vicinity. For males, fights are more serious; in 30% of such fights a male is killed. And if a male is killed it is always the resident, never the intruder.