SPEAKER 1: One of the interesting avenues that we're following up now is that since we started to mark many chicks beginning in 1998, essentially saturation banding of all the chicks that are produced in our territory, and 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 ABJ, 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 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 its 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, on this territory. And so it's giving us a great deal of exciting information.
By quality, I mean the potential of that territory to produce chicks, which is the evolutionary goal of loons and all animals, so to speak. And so quality has to do with certainly the number of fish that are available in the lake. There has to be a large enough lake with enough food, chiefly fish, for them to be able to feed their young. But most lakes in this area meet that threshold. And so the more critical dimension is nesting habitat. Does the lake have marshy areas-- boggy areas often are favored by loons-- or islands because islands and marshy areas tend to be less visited by things like raccoons, fishers, foxes, skunks, which are substantial predators on loon eggs.
And so, you might have one lake that has a large island far from shore where even the most courageous raccoon is likely to swim to. And if the loons place a nest there, they're likely able to produce chicks year after year after year on that territory. On the other hand, you might have another lake where it doesn't have any islands at all, maybe all of the shoreline is upland and not boggy. It doesn't have any marshy, emergent vegetation where they could nest and maybe get the nest far from shore and protect it from raccoons and other predators. So lakes do vary enormously in their intrinsic quality.
Loons don't mate for life. There are takeovers that occur. 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 territory.
There's a major difference between males and females. We initially thought that there wasn't much difference. But if you have a pair on a lake and a male intruder comes in and he's able to displace the established resident male on the lake, that resident male would move somewhere else and the usurper would pair quickly with the resident female. And that certainly occurs, and that occurs among females too. An intruder female can come and displace the resident female and pair.
This is the bird that's the apparent victor, at least in that round. Looked pretty roughed up anyway. That's the resident female after she's been driven on to shore after that chase. . As we started to look at our data more closely and reports started to roll in of dead loons occurring on territories, we realized there was a pattern. And the pattern was pretty clear that male loons often die in the context of a territorial takeover, and female loons don't.
And so it appears, and in fact, the loons that are dying are-- it'll be a battle between the resident male and intruder male. And the loons that are dying are the resident males. And so it appears-- and we're still learning about this. This is still a topic for investigation-- but it appears that resident males are fighting too hard sometimes for their territories and paying with their lives for it.
SPEAKER 2: This chase around the lake lasted for 16 minutes.
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 territory, whereas, females do not. And so, that is consistent with the idea that perhaps males 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, and what you find is that it's males that are the ones that are looking for the nest, or their the ones that are positioning the nests. And, therefore, males are the ones that year after year remember where the good nest sites are. We know that the males also reuse good nest sites, and they avoid bad nest sites. And so over time, males accumulate useful information about their territory. It makes that territory uniquely valuable to them.
Male loons have a very simple rule, as do many species of animals. And that rule is, it's called the win-stay loose-switch rule. And it just means if you succeeded in producing chicks or produce young at a certain breeding site, reuse that site-- very common sense rule of thumb that many animals employ. 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 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. 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.
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Common loons are large, fish-eating birds that winter on the ocean but breed on freshwater lakes. Loons have been studied for years, but it is only in the last fifteen years that we have a large enough population of banded individuals to begin to understand the details of their behavior. Breeding territories can be founded on vacant lakes by replacing a missing pair member or by actively evicting a member of the pair. When an intruding female takes over a territory, the displaced female moves to an adjacent lake. In contrast, when the intruder is male, about 30 percent of the territorial battles are fatal. If a loon is killed, it is always the resident male, never the intruder. We don't know why there is this asymmetry in the behavior of the two sexes. But since it is the male loon that seems to select the nest site with improving reproductive success every year, this may be the reason.
Many of us know loons by their haunting vocalizations. There are three long distance calls: the wail, the tremolo, and the yodel. Each plays a role in the establishment and maintenance of the breeding territory.
Loons are at the top of the food chain and tend to accumulate toxins, like methyl mercury, in their tissues. One reason for studying loons is to see whether an increase in mercury has any effect on their reproduction or behavior. These CyberTower videos describe how this research is conducted.
This video is part 5 of 6 in the Understanding Loons series.