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PRI's Environmental News Magazine

New Threat to Bald Eagles

Air Date: Week of February 13, 1998

The bald eagle was headed for extinction in the 1960s de to DDT, that caused eagles to lay eggs with thin shells. Since then the ban of DDT in 1972, eagle populations have slowly rebounded. Now, there is a new threat. In 1994, fishermen found an eagle carcass on Degray Lake near Little Rock. So far, wildlife officials say, at least, 55 eagles have died from unknown causes there and at two nearby lakes. The duck-like water fowl the American Coot, is also affected. Dr. Kimberli Miller, a veterinarian at the National Wildlife Health Center in Madison, Wisconsin, is helping coordinate research on the die-off. She told Steve Curwood that before they perish, the birds develop a mysterious illness.

Transcript

CURWOOD: Chosen in 1782 as our national emblem, the majestic bald eagle was headed for extinction in the 1960s. The turning point came with the 1972 ban on the pesticide DDT that had caused eagles to lay eggs with thin shells. Since then, eagle populations have rebounded. Now, there appears to be a new threat. In 1994 fishermen found an eagle carcass on Degray Lake near Little Rock, Arkansas, Then they found another, and then another. So far, wildlife officials say, at least 55 bald eagles have died from unknown causes there and at 2 nearby lakes. The American coot, which looks like a duck or a goose, is also affected. Dr. Kimberli Miller, a veterinarian at the National Wildlife Health Center in Madison, Wisconsin, is helping coordinate research on the die-off. She told me that before they perish, the birds develop a mysterious illness.

MILLER: Sick birds in the field have been observed flying into rock walls, flying into trees, flying very wobbly. The coots have been described as looking like they're drunk, almost. They will walk along the ground, putting their wings out for balance. Some birds have been observed on their backs in the water with their feet in the air, trying to swim. They end up swimming in circles.

CURWOOD: Now, eagles are birds of prey, although they're also rather scavenger-like, aren't they, in the wildlife?

MILLER: Yes, that's true. They will feed on anything that's available, and certainly carcasses along the road or on the shore are very easy prey to catch. And they also will eat fish and ducks, coots.

CURWOOD: So if eagles eat water fowl like coot, do you think that the eagles are getting this illness from the coot? Or is there some other reason why both birds, and only those two birds, are being affected?

MILLER: That certainly is one possibility that the eagles are becoming affected by eating affected coots. Or, it could be that the coots and the eagles are coming in contact with the same disease agent independently of each other.

CURWOOD: Is there anything that you've learned so far about what's causing this problem?

MILLER: We really feel that what we're dealing with here is some type of toxin. When you look at the birds, they're in good body condition. They have good fat stores. They look like they should be healthy birds. But the only consistent finding in the eagles and in the coots is a small, microscopic change in the brains and the spinal cords of these birds. And this lesion, this change that we're seeing, there's only some very specific things that are known in the literature to cause that type of change.

CURWOOD: If there's a toxin in the environment that's causing this, what could it be? What kind of toxins cause these changes in the brain, these lesions that you say are there?

MILLER: Well, the things that are known of in the literature to cause this, it's a pretty short list. There's a rodenticide that has been associated with this. There are toxic plants in South Africa and Australia that have been associated with this. Some human medications for tuberculosis or copper deficiency.

CURWOOD: Are there any signs of toxins in the bodies of these birds?

MILLER: No, not really, in terms of toxins showing up in the tissues that we've examined. We're really not finding anything significant that will point us toward the answer as to what's going on here. Actually, one thing I should point out is that this year, we found coots on a lake in North Carolina and a lake in Georgia that have the same neurologic lesion.

CURWOOD: So, this is quite a mystery. Somehow, something is happening, you think it's likely a toxin and yet you can't find the toxin.

MILLER: It's certainly possible that whatever it is may only be present in the body for a short time. And so, perhaps, you know, we're seeing the manifestations of the problem, but perhaps the compound can no longer be detected. Or perhaps we're not using the right analytical method to pinpoint what that compound might be. There are a lot of questions, and you're right, it is a mystery as to just what it is that is causing the microscopic change that we're seeing in these birds. And that's something that we're working very hard at trying to determine, so that we aren't continually faced every fall and winter with mortality in eagles at these sites.

CURWOOD: Kimberli Miller is a veterinarian and wildlife disease specialist at the National Wildlife Health Center in Madison, Wisconsin. Thank you so much, Dr. Miller, for taking this time with us.

MILLER: Thank you, Steve.

 

 

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