SPEAKER 1: Loons face a number of threats in their environment. In the first place, as we've seen, they breed on freshwater lakes, and freshwater lakes are highly desirable for summer recreation, both building cottages around the lake and for the use of the lake itself for recreation. This causes a real problem. It causes a problem in several ways.
First off, there's the problem of a place to nest. If the shoreline is all developed into lawns and houses, there's no suitable place for the loons to nest. Some loons become very tame. This loon nest is close to both docks and houses.
Secondly, there is the interference from jet skis, speedboats, even canoes that cause wake and disrupt the nesting, or distract the parents and the baby loons. In some parts of the country, lakes have a tremendous variation in their water height. They're used to hydroelectric power, and therefore they're high in the spring.
And then, as the season progresses the water is drawn down. And so the loons find themselves a long, long way from the water, and their nests fail. Or alternatively, a large thunderstorm upstream causes the water level to rise, submerging the loon's nest.
The solution to those problems is floating nest platforms. This nest platform is made of PVC pipe and plastic mesh. Loons nested on it successfully this year.
Another difficulty that loons have is lake acidification. Power plants and so on have caused an increase in acid rain. This has caused lakes, particularly in the Adirondack section of New York, to become highly acid. And as they become acid, they are unable to support a sufficient fish population for the loons to survive on. And as a result, the loons are extirpated.
SPEAKER 2: Perhaps more importantly, loons accumulate methylmercury. And they accumulate what appear to be dangerous levels of methylmercury. This has not been a topic of study for us, in particular, but we know that they accumulate these levels of methylmercury that can be harmful.
And so, since mercury levels are rising currently, largely as a result of human impacts, it's important to monitor loon populations in order to see what the potential health implications of mercury is on fishes that loons eat and also humans consume. It's coming from a variety of sources. There's a natural amount of methylmercury in the system. There's sort of a baseline level.
But it also comes from, I guess, paper pulp processing plants, coal burning plants as well-- that are generating electricity. So naturally, those levels of mercury have increased somewhat. And loons already, at least in northern Wisconsin, appear to be at a potentially dangerous, hazardous level. And so the likelihood that the level of mercury is rising still further is cause for concern.
SPEAKER 1: Loons apparently forage on the bottom to pick up stones for their gizzards. That's how they grind up their food. And if they find lead sinkers, they will often ingest these lead sinkers. And it turns out that one lead sinker is sufficient to poison a loon. And therefore, it's very important for fishermen to substitute other kinds of metal for lead. And there are programs around the country where one can take one's lead sinkers into a place and exchange them for those made out of a less toxic metal.
Finally, there is the problem of botulism. In the Great Lakes particularly, there are fish which apparently have the botulinum toxin in them. And so loons eating these fish, I think particularly gobies, are often killed. And substantial numbers of loons are killed every fall on migration in the Great Lakes. And that's an obvious problem.
In addition, there are things like oil slicks. In the wintering grounds of the loons, there was a big spill off Rhode Island some years ago that killed several hundred loons due to oil contamination of their feathers. There are problems of gill netting in the Great Lakes, gill netting for fish. And the loons chasing the fish also get tangled in the gill nets and drown. So it seems that there are all sorts of problems that beset loons. And it's really remarkable that they're doing as well as they are.
But in part they're doing that well because people care about loons. One of the real tricks was to get lake owners to care about the loons on their lake. And once they do that, they serve as a much better police force than the game wardens and so on. Because the lake owners are there, and they can go out to people who are disturbing the loons and say, hey, don't disturb our loons.
And as a result of that, the breeding rate, particularly in New England, I think, has increased quite dramatically. The use of signs at the entry way to lakes cautioning fishermen and recreational boaters about the fact that this is a lake that is used by loons to breed is also an important way to go. So I think overall the situation is really relatively cheerful for loon populations. But in order to be effective, all of us are going to have to work hard in our various ways to understand loon biology, to understand what kind of mitigating factors we can apply, and then to apply these findings in the real world to preserve loon populations.
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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 3 of 6 in the Understanding Loons series.