Band-tailed Pigeons (Patagioenas fasciata) wintering at Hastings Reservation in central coastal California during winter 2006–2007 died in large numbers between January and March 2007. Laboratory analysis of carcasses indicated that Trichomonas gallinae was responsible for the die-off. During the height of the die-off, a survey of 2.5 km of suitable riparian habitat resulted in 373 pigeon carcasses being found. Based on a subsample of carcasses, mean turnover rate was 2.8 days with a 95% confidence interval of 2–10 days. Extrapolating to suitable habitat over the 52.7-km² study area resulted in a conservative estimate of 43,059 dead pigeons, assuming a conservative carcass turnover rate of 10 days. This estimate of mortality is nearly three times the largest trichomoniasis mortality event previously recorded for Band-tailed Pigeons and at least twice the number harvested annually in the United States. Local mortality of pigeons in Monterey County, California may have been several times this estimate based on the presence of considerable similar habitat in the nearby Ventana Wilderness.