The program is one of a number of experiments in giving contraceptives to nuisance animal populations including deer, squirrels and pigeons, which may carry disease, damage farmland or compete with native species for food, the Los Angeles Times said.

Some 300 Hollywood pigeons are eating OvoControl P in pill-shaped kibbles in a pilot program that hopes to half the city's pigeon population by 2012, the Times said.

Trials for such birth control programs have been supported by animal-advocacy groups including the Humane Society of the United States and People for the Ethical Treatment of Animals.

A 2004 squirrel contraceptives trial in Berkeley, Calif., reduced birth rates by 66 percent, according to Alameda County and U.S. Department of Agriculture statistics. Last summer, 80 does at Point Reyes National Seashore were injected with GonaCon to see if it will slow herds of deer, which dig up land, carry exotic diseases and compete with native deer and elk for food and shelter, the Times said.