Ask the Experts '97

QUESTIONS AND ANSWERS

1. How do frogs hear?
2. I spend my summers at Matlock Manitoba. Over the summers I have noticed the frog population of Nothern leopard frogs and wood frogs has decreased. Yet this summer there was a huge increase. Has this happend in Minnesota too?
3. I catch frogs in the ditches near Lake Winnipeg in a cottage area. As the frog populations decreased I never saw a deformed frog and as the populations increased I never saw any either. Is it strange not to see any deformed frogs when the population is increasing? Or is it just really good news?
4. Why do frogs have nucleated red blood cells (RBC)?
5. If I wanted to start caring for some tadpoles now, how could I care for them in an aquarium? I live in the north west part of Minnesota and would like to have some frogs next spring. I believe that some tadpoles overwinter in my area. Can you help?
6. I have seen many frogs but never heard of any endangered frogs. Are there many endangered frogs?
7. We have noticed that frogs collect in our window wells. We think that they do this because: they are trying to get away from the wind; for warmth; it's damp; and there are bugs available for food. Are our assumptions correct?
8. We know that frogs breathe through their skin and that the skin can carry toxins. Does their skin have other important jobs?
9. We have read the recent reports on frog deformity causes--the pollutants in the water and the UV light. What do these do to the eggs to cause the problems?
10. Are you finding more deformed frogs than toads as we suspect? We ask this because the frog spends more of his life in the polluted waters.
11. Concerning the contaminated ponds where the frogs are being found, are fish or other animals also showing up deformed? If not, is it because the frog's skin is so sensitive?
12. Are there other suspected causes of the deformities other than pollution and UV light?

1. How do frogs hear?

Harris: Frogs hear in a similar way to the way that humans hear. However, a frog has a thin membrane called the tympanic membrane which can be flush with the side of their head and is located behing the eyes. They pick up sound waves in almost the same range as humans. I would recommend that people interested in this, read Duellman and Trueb's "Amphibian Biology" (1985).

Moriarty: Other books that discuss hearing in frogs are: Holmes "Biology of Frogs," Wever "The Amphibian Ear" (this is a major academic monograph).
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2. I spend my summers at Matlock, Manitoba. Over the summers I have noticed the frog population of Nothern leopard frogs and wood frogs has decreased. Yet this summer there was a huge increase. Has this happend in Minnesota too? (Submitted by Ken McCullogh, Canada)

Moriarty: There are a number of reasons why frog populations fluctuate. The main one being drought. In Minnesota, in the mid-1980's we had a series of drought years which caused a major decrease in frog populations. The dried up wetlands limited breeding sites and the dry uplands caused increased mortality because of improper microhabitats (moist grass or leaf litter). Our frog populations have been increasing since 1991 and are back to normal levels.
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3. I catch frogs in the ditches near Lake Winnipeg in a cottage area. As the frog populations decreased I never saw a deformed frog and as the populations increased I never saw any either. Is it strange not to see any deformed frogs when the population is increasing? Or is it just really good news? (Submitted by Ken McCullogh, Canada)

Moriarty: The presence or absence of malformed frogs is not tied into the population densities, but rather the habitat quality. While researchers do not know the exact cause, it is now thought to be caused by something in the water. You may be fortunate in not having this contaminant in the Lake Winnipeg area. You should know that, even though the news reports make it sound like most of Minnesota's frogs are malformed, most of our frogs are very normal and healthy.
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4. Why do frogs have nucleated red blood cells (RBC)?

Harris: This is a good question, and scientists aren't sure. Nucleated RBCs means that the cells have a nucleus present in them. Some think that a better question might be "Why do some animals, like humans and birds, have non-nucleated RBCs?" A good source for frog-related anatomical questions is "Biology of Amphibians" by William Duellman and Linda Trueb (1985).
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5. If I wanted to care for some tadpoles now, how could I care for them in an aquarium? I live in the north west part of Minnesota and would like to have some frogs next spring. I believe that some tadpoles overwinter in my area. Can you help? (Submitted by Cay Donlin, Thief River Falls, Minnesota)

Moriarty: In Northwest Minnesota the only frog that will overwinter as a tadpole is the Northern Leopard Frog. They can be raised in aquaria over the winter, but will go through metamorphis early, if they are fed and kept warm. You will end up with frogs in January!
It would be better to collect some Wood Frog or American Toad eggs in the spring and raise them. They grow rapidly and should go through metamorphis in early July.
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6. I have seen many frogs but never heard of any endangered frogs. Are there many endangered frogs? (Submitted by Mike Harney)

Moriarty: Any endangered frogs are very rare and hard to find. In Minnesota, there is one endangered species, the Blanchard Cricket Frog. In the United States there are a number of species. Two include the Houston Toad and Wyoming Toad. There are several species in California. For further information you should check the US Endangerd Species List published by the Fish and Wildlife Service. Species from other countries can be found on the CITES list.
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7. We have noticed that frogs collect in our window wells. We think that they do this because: they are trying to get away from the wind; for warmth; it's damp; and there are bugs available for food. Are our assumptions correct? (Submitted by The Friends of the Frog and Phenology Group, Valley Crossing Community School, Woodbury, MN)

Moriarty: They are all very good assumptions but the frogs are in the window wells for a very simple reason--they are traps. The frogs are moving from one habitat to another (marsh to upland, etc.) and encounter a foreign object (house) blocking their path. As they try to get around the house they fall in the window wells. During frog migrations, it is helpful to check window wells on a daily basis and remove the frogs. Move them away from the house and let them go.
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8. We know that frogs breath through their skin and that the skin can carry toxins. Does their skin have other important jobs? (Submitted by The Friends of the Frog and Phenology Group, Valley Crossing Community School, Woodbury, MN)

Moriarty: Skin is also important in the regulation of water uptake by frogs. Frogs don't really breathe through their skin, except under very cold water condition, such as hibernation.
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9. We have read the recent reports on frog deformity causes, the pollutants in the water and the UV light. What do these do to the eggs to cause the problems?

Moriarty: We don't know exactly what the effects of the pollutants are on eggs. The actual time period when the deformities take place has not been determined. See next question. (Submitted by The Friends of the Frog and Phenology Group, Valley Crossing Community School, Woodbury, MN) Return to top of page

10. Are you finding more deformed frogs than toads as we suspect? We ask this because the frog spends more of his life in the polluted waters.

Moriarty: Very good assumption. Several researchers have found that the more aquatic, or the longer the tadpole stage, the higher the level of deformities. Species such as toads, treefrogs, and wood frogs, have relatively short tadpole stages and the adults are terrestrial. Low levels of deformities have been found in these species.
Green and Mink Frogs have long tadpole stages and the adults are highly aquatic. The highest defromity rates have been found in these species. If the deformities were tied to the eggs then all species should have the same deformity rate. (Submitted by The Friends of the Frog and Phenology Group, Valley Crossing Community School, Woodbury, MN)
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11. Concerning the contaminated ponds where the frogs are being found, are fish or other animals also showing up deformed? If not, is it because the frog's skin is so sensitive?

Moriarty: Other deformed animals have been found including turtles, birds and fish, but not in the numbers as in frogs. Deformed fish are much harder to sample. Anyway, if they die they sink or are eaten. Deformed birds are regularly reported in other parts of the country, but not in association with frogs. The frogs skin is not the cause of increased sensitivity. (Submitted by The Friends of the Frog and Phenology Group, Valley Crossing Community School, Woodbury, MN)
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12. Are there other suspected causes of the deformities other than pollution and UV light?

Moriarty: The causes, including increased UV radiation, is probably caused by some sort of pollution. The Minnesota Pollution Control Agency also suggests that it may be a natural toxin. However, if it turns out to be a chemical, a heavy metal (such as lead, mercury, etc.), or increased UV, this is caused by humans. While the exact causes have not been determined, scientists are getting closer to the answer. If it does turn out to be caused by humans, then we are the only ones who can solve this.

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