ST. PAUL —  The city of St. Paul is taking a hard line against its growing pigeon population by mixing a contraceptive into bird feeders on roofs in the downtown area.

The contraceptive, OvoControl-P, prevents bird eggs from hatching by blocking development of the layer between yolk and egg white. The pellets don't harm the birds, and the plan has the backing of People for the Ethical Treatment of Animals.

The pesky birds have been making quite a mess in parts of downtown, St. Paul officials said.

The area around the Lowry Building and Lawson Commons is "a disgrace" thanks to all the pigeon dung, said Bob Kessler, the city's chief safety inspector.

City skyways are also being outfitted with mechanisms meant to deter pigeon roosting. It's all part of an effort to spiff up the city before the Republican National Convention later this summer.