I'm a student of roadkill. I keep an informal tally of the carcasses I spot on the roadside – what kind, how many and where -- and I note the splatters that accumulate on our car windshield. They're an indication of the diversity and abundance of animal and insect lives along the unnatural transects we call highways.

I know when spring has arrived in my southern Colorado valley as much by the increase in mangled mule deer on the roadside as by the pale green tint that washes this high-desert landscape. The up-tick in deer kill comes when these grazers home in on the smooth brome grass planted on the road margins by the highway department; the brome greens up before the native grasses, providing early and nutritious -- if risky -- grazing.

Similarly, the progress of the Arkansas River caddisfly "hatch" is just as easily read in the numbers of winged adult caddisflies smeared on vehicle windshields, and the quarts of wiper fluid used to remove them, as it is by the number of anglers in the river.

Roadkill may seem like a macabre measure of biological diversity, but it provides interesting, if wrenching, information. It wasn't until I read a recently published study, however, that I realized roadkill also tells us something about the species doing the tallying – and the killing.

In 17 months of roadkill census, researchers at Purdue University found 10,500 carcasses representing more than 65 species of wildlife, most of those from a one-mile stretch of highway traversing a bog. I was so shocked by those numbers that I had to read them twice: 10,500 animals killed on the road in less than two years. And the total carnage may actually have been five times higher. There wasn't enough left of many of the carcasses to count, and  larger animals often manage to make it off the road before they die and are therefore not discovered.

Perhaps the mortality is less shocking when you learn it was mostly frogs: bullfrogs, leopard frogs, and other frog species. The other dead included deer, opossums, raccoons, chimney swifts, garter snakes and salamanders.

Thousands of dead frogs may not seem like much of a concern. But frogs are one of the threads that weave the webs of relationships we call ecosystems, the natural "technology" that keeps our planet green and habitable.

Frog tadpoles chow down on mosquito larvae by the mouthful, keeping populations of the blood-sucking and disease-carrying insects in check without deadly insecticides. Frogs are also a major food source for larger species, from trout and river otters to bald eagles. Massive frog roadkill thus deprives other wildlife of food. Worse still, it attracts other creatures to the road to feed on the dead.

The study's authors suggest that roadkill may be an as-yet-unexamined factor in the worldwide crash of amphibian populations, including the frogs and toads once captured by the jar-full by children throughout North America.

The researchers propose some solutions: Don't route roads through wetlands, provide wildlife with routes over roads or through underpasses, and fence highways to keep wildlife away from the killing zone.

Those are all very nice, but it seems to me that they fail to tackle the underlying problem. And that problem is, of course, overpopulation -- not on the part of the wildlife, but on the part of the species doing the road-killing and the tallying -- Homo sapiens. Us.

There are too many of us. The world's human population has reached nearly 6.7 billion, twice as many people as there were 50 years ago; we're adding another million humans about every four days.

We're the ones building the roads. We're the ones driving the cars. And no, the rise in the price of gas isn't expected to curtail driving enough to really benefit wildlife; it's just likely to push drivers into smaller vehicles. With so many of us, there is simply less room, less food, less habitat, less chance of "them" surviving -- the other 1.8 million known species with whom we share this planet.

Hence the 10,000-plus frogs killed on a one-mile stretch of road. And the wars, the shortages of food, water and fuel, and global climate change. We're the source of the problem. And we're ignoring it. What if we acknowledged that our overpopulation is a serious issue? What if we said it out loud: There are too many of us.

There. The sky did not fall, the world did not end. Let's acknowledge our overpopulation, and do something about it, before it gets worse. The frogs and caddisflies and deer and the ecosystems they participate in will thank us.

Susan Tweit is a contributor to Writers on the Range, a service of High Country News (hcn.org). She is a writer and naturalist in Salida, Colorado.