QUESTIONS AND ANSWERS
QUESTIONS WITH ANSWERS
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).
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.
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.
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).
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!
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.
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
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.
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
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.
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,
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.