ST. PAUL, Minn. – Pounded and strained by heavy traffic and weakened by missing bolts and cracking steel, the failed interstate bridge over the Mississippi River also faced a less obvious enemy: Birds, specifically pigeons. […]

Experts say the corrosive guano deposited all over the Interstate 35W span’s framework helped the steel beams rust faster.

It’s easy to overlook the quiet, cumulative power of the ubiquitous animals we take for granted. But as Andy Goldsworthy remarks in Rivers and Tides, the individual sheep may be vulnerable and weak but the “river of sheep” flowing for hundreds of years changed the landscape of Britain. So why not a river of superdoves flowing erosively through our cities, persistent enough to outlast them?