In fact, their droppings, we originally valued as fertilizer.

Indeed, their poop, which we originally cherished as fertilizer, presents a unique problem. Just one pigeon can leave behind 11 kilograms of acidic excrement per year, which, in the United States, scales to about $1.1 billion in structural damage annually. Though incidents of infection are rare, this poop can host fungi that are harmful to people if inhaled. They may be numerous, noisy and a little too keen on your lunch, but the pigeons that swirl around us are evidence of an ancient, ongoing relationship. Their rise to world domination has been a collaborative effort. For better or for worse, we did this to ourselves.