When I heard the Minneapolis bridge collapsed, I just assumed that it was partly caused by the salts used to make driving safer.

But today there are reports that dung dropped by pigeons nesting beneath the girders might have contributed to the corrosion.

“There is a coating of pigeon dung on steel with nest and heavy buildup on the inside hollow box sections,” inspectors wrote in a 1987-1989 report.

In 1996, screens were installed over openings in the bridge’s beams to keep pigeons from nesting there, but that didn’t prevent the building of droppings elsewhere.

Pigeon droppings contain ammonia and acids, said chemist Neal Langerman, an officer with the health and safety division of the American Chemical Society. If the dung isn’t washed away, it dries out and turns into a concentrated salt. When water gets in and combines with the salt and ammonia, it creates small electrochemical reactions that rust the steel underneath.

This photo is from ABC NEWS and shows how pigeons might have caused the problem

The problem of corrosion is not limited to bridges.

This link at the Nasa Corrosion technology Center discusses the problem, and shows a photo of a hydroelectric dam that developed corrosion from bird droppings.

As a doctor, the main bird related disease I have seen is Histoplasmosis, a fungus. Luckily, most of the cases I’ve diagnosed were old cases where we saw the scars on Chest X Rays.

But there are other serious  diseases such as Cryptococcus and Psitticosis, stuff we learn about in medical school mainly because the diseases are often missed if you don’t think about them when a person comes in sick. The worse one is cryptococcal meningitis, a rare disease that is more common in people with HIV or bad immune systems.
This NewYork City site has a list of pigeon related diseases, and how to clean up bird droppings.

And if you live in cities with pigeons and like the birds, Cornell has a page on birdwatching  in the city that tells you all about the critters.

Pigeons have even been given backpacks and put to work monitoring smog in California.

Each bird will carry a GPS satellite tracking receiver, air pollution sensors and a basic mobile phone. Text messages on air quality will be beamed back in real time to a special pigeon “blog”, a journal accessible on the internet.
Miniature cameras slung around the pigeons’ necks will also post aerial pictures.

Leading humorist Dave Barry to comment :

Only (scientists) they could think up a scheme whereby we fight pollution using a critter whose primary environmental activity is pooping all over the environment.

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Nancy Reyes is a retired physician living in the rural Philippines, where there are a few small doves and lots of sparrows but NO pigeons. Her website is Finest Kind Clinic and Fishmarket.

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