One particular problem with our industrial age is the proliferation of chemicals and concentrations of unnatural substances in the environment. I'm using the term "unnatural" here in a very basic sense: not naturally found in the environment. I don't presume to have the knowledge to judge what harm these substances can cause.

There's something creepy to me in this soup of hundreds of thousands of artificial compounds entering the environment and the food chain. Again, I'm using "artificial" fairly narrowly: produced by people not nature. I admit I'm not entirely rational about it. It can't be good to have these chemicals ingested, put on our skin, sprayed in our gardens, spewed from autos, etc. The longevity of their existance particularly worries me. And the way some concentrate up the food chain. Some fish and mercury is a good example. There are some fish you shouldn't eat more than once a month because of the toxicity of the mercury in them.

Which brings me to birds and DDT. You remember DDT: It's a pesticide banned in the US in 1972. Except the US used about 1.4 billion pounds of it between the end of WWII and then. Oops. And now it may be causing the decline of non-migrating songbirds in the US. Non-migrating means they didn't pick the DDT up in another country, they ingested it here. Wisconsin is moving towards authorizing hunting feral and uncollared cats because they are blamed for the decline of songbird species. Um, maybe not?

The following is from Old Culprit hits Birds - Maybe:

The results were intriguing. Traces of DDT and other related chemicals were showing up in the birds. But the real shock came when Dr. Harper, a biology professor at Illinois Wesleyan University in Bloomington, compared his results with DDT levels in nonmigrating songbirds. These year-round residents of North America - including a who's who of birds like the northern cardinal, black-capped chickadee, and dark-eyed junco - had more kinds of chemicals and dramatically higher levels of them than the migrating species.

Those are surprising results. Heavily restricted in the United States since 1972 and a declining problem for eagles, osprey, and other predatory birds, DDT continues to show up in alarming levels in nonmigrating songbirds. Does that spell trouble ahead for these still-healthy species? Are humans at risk? No one knows. But one lesson seems clear: Beware of what you put into the environment, because it can be extraordinarily difficult to remove.

"These [findings] are reminders that our decisions are going to affect us for decades," says Greg Butcher, a senior scientist with the Audubon Society and author of a recent "State of the Birds" report that showed many North American species in decline. "There may not be a toxic effect that kills birds at these levels. But it very well could affect their embryonic development."