Can you tell me what high levels of aluminum in our waterways may be doing to bird reproduction, behavior, and food sources? 
—Francis Mangels, Mt. Shasta, CA

Exposure to metals, even those like aluminum that occur naturally in the environment, can impair the physical and developmental health of birds and other animals. Aluminum, one of the most abundant metals on earth, is often found in soils. When acid rain falls, aluminum leaches out of the ground and into lakes, streams, and other water bodies, where it can be absorbed by aquatic organisms.

Aluminum is highly toxic to fish and other wildlife, and can lead to salt imbalances, heart conditions, and reproductive problems. Once it’s in water, it can cause blood vessels in fish to pop, or it can be ingested by animals higher up the food chain, like dippers and waterthrushes, causing lower reproductive success. 

Acid rain reduces available calcium in the soil—a major issue for birds, says Christy Morrissey, a postdoctoral fellow at Cardiff University in the United Kingdom. The soil’s reduced calcium affects animals like snails, which make their shells out of the element. Birds then ingest smaller amounts of calcium when eating the snails, leading to less bone mass, thinner eggshells, and fewer healthy chicks. These conditions can be exacerbated by aluminum, which takes the place of calcium in the ecosystem.

Clean Air Act amendments called for the 1980 levels of sulfur and nitrogen emissions—the two major components of acid rain—to be halved by 2010, a goal already met. Representative John M. McHugh (R-NY) introduced legislation earlier this year calling for greater decreases. You can blame the problem on the rain, but keep fighting for action.
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How can I prevent black bears from eating my birdseed and trash?
—Jason Stone, Fairfield, CT

If you hear something go bump in the night, chances are you have a birdseed bandit.

People who leave bird feeders hanging in their yards, garbage cans on the curb, dog food on their porches, or food at their campsites are likely to hear black bears rummaging around after dark. Wildlife managers call this phenomenon “food conditioning.” Black bears, which live throughout much of North America, are the poster animals for this problem, but others, including raccoons and skunks, have rap sheets, too.

Of course, if Smokey could talk, he might remind us that while he’s trespassing in our backyards, we’re also trespassing in his. Prevention is the best tactic for avoiding conflicts with hungry wildlife, says Sean Matthews, a biologist with the Wildlife Conservation Society, because once an animal is effectively conditioned to get a treat somewhere, it will keep coming back.

“Human food is pretty tasty, it has a lot of calories in it, and bears recognize it as a high-quality meal,” says Matthews. “Bears may end up spending more time on your back porch as opposed to in the woods eating berries.” Not surprisingly, gorging on junk food is also bad for bears’ health. Wildlife officials working in the area around Gatlinburg, Tennessee, have caught and relocated dumpster-diving male black bears that tipped the scales at 600 pounds, an “exceptional” weight for even a very healthy old boar.

If a bear develops a habit of snacking around the proverbial picnic table, wildlife managers might have to take more drastic measures to avoid dangerous conflicts with humans. “A fed bear is a dead bear,” as some say, because sooner or later that conditioned bear is going to get itself killed. It might be hit in traffic trying to get to a good meal, or worse, it could be shot. Fed bears are easy targets for hunters and a challenge for wildlife managers who are also charged with keeping human parkgoers safe.

Bears are most prone to getting into trouble in spring, when they are coming out of hibernation and there isn’t a lot of food available, and in late fall, when they are trying to bulk up before their long winter’s naps. Still, they have been known to steal food in summer, too.

You can encourage wildlife to stick to a natural diet by using sealable containers for food when you are camping. (Studies show bears bypass the campsites that have the bear-resistant canisters and spend more time investigating sites where food is hanging, says Matthews.) At home, try putting your garbage out the morning of trash day, keeping your dog food in the house, and, if you find bears snacking, storing your bird feeder from April 15 to Halloween. Take the preventive approach before the problem becomes too much to bear.
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Send your most vexing questions to greenguru@audubon.org.