By Staff
I remember as a kid, and I bet you more seasoned readers do too, that leopard frogs were as common as ticks here in southern Michigan. Wander along any stream bank or lake shore and these bright green frogs with prominent black spots would be bounding from underfoot in long, zig-zagging leaps. Savvy bass and trout anglers used them as bait. They were so common you didn't give them any thought.
Somewhere along the line, though, they quietly slipped into oblivion. One day we looked around and said, "Hey, where have all the frogs gone?" This happened decades ago and you know what? We're still asking the same question today. And it's not just here in southern Michigan. The decline of many amphibian species is happening all around the world. It just happens the leopard frog is one of the more obvious in our area.
Of course, once this decline came to light the scientific community jumped all over it to come up with a reason. The old standby excuse of habitat loss wasn't going to work here. Over the years leopard frog decline has been fertile grounds for all manner of studies. Many experts feel that leopard frogs are an indicator species, meaning they are sensitive to bad things happening to their habitat and if they start to decline you'd better open your eyes and start paying attention. One of the first things discovered was that many of the remaining leopard frogs had odd deformities, not enough legs, too many legs, tails, and so on. The question was why.
One of the earlier findings suggested acid rain was the culprit. Pollution in the air, primarily from burning fossil fuels, is picked up by rain drops increasing the acid content of the rain water to that of tomato juice. In the most extreme cases it killed the frogs outright. At lesser levels it appeared to be a cause of these deformities. While plausible and valid, this didn't seem to be the entire cause, though. Another finding makes a lot of sense. Frogs breathe through their skin as well as their lungs. Frogs are constantly in contact with the ground where bad stuff from pesticides, herbicides and all manner of chemicals from plastic compounds to road deicers accumulate. Injurious chemicals are absorbed through the frog's skin and some have proven to cause deformities and death.
However, these causes still don't tell the whole story and research continues. Not long ago a newly found fungus called chytrid was found prevalent in many leopard frog populations. This also appears a likely culprit. Other studies have shown that depletion of the ozone layer is allowing record levels of UV radiation to reach the earth's surface and some species, possibly leopard frogs included, can't tolerate it. They're getting nuked. Another suggested culprit of deformation is human female hormones from birth control pills entering waterways via sewage systems.
Then there's the new study by Berkeley biologists which points a finger at the herbicide Atrazine, the most widely used herbicide in the grain growing belt, which happens to coincide with the range of the leopard frog. Traces of Atrazine are found in virtually all Midwest waterways. At just one 10th part per billion in water it feminizes male frogs, turning their testes into ovary-like glands. That quantity is 30 times less than the allowable amount of Atrazine in our drinking water.
All of these causes have proven valid to some degree and most experts feel the decline of our leopard frogs can not be attributed to just one thing but a combination of many. But the bottom line is still as the Michigan DNR publicly states – the numbers of leopard frogs, once the most abundant frog in the Great Lakes, have fallen, in some areas to rarity; the reasons unclear; the frog's status unknown. Carpe diem.