Timing (mean birth date) and synchrony (variance around that date) of births can influence survival of young and population growth in ungulates. We quantified timing and synchrony of births in 2 populations of bighorn sheep (Ovis canadensis) that were acquired from different source herds and reintroduced to adjacent areas. From 2001 to 2007 we recorded 121 birth dates to test whether timing and synchrony of parturition were similar between populations. Furthermore, we calculated population-wide survival of young to their 1st winter. Females on Mount Timpanogos gave birth later than females inhabiting Rock Canyon from 2001 to 2002 and in 2004; those females gave birth earlier in 2007 than females inhabiting Rock Canyon. Timing of births was similar in 2003 and from 2005 to 2006. The relationship between differences in mean birth dates between populations and time since reintroduction was marginally nonsignificant (P  =  0.075), whereas differences in synchrony of births were negatively related to time since reintroduction (P  =  0.005). Survivorship of young was higher for females in Rock Canyon that gave birth on average 30 days earlier from 2001 to 2002 and during 2004 than for females on Mount Timpanogos during those years. Our findings provide evidence that within 5 years after reintroduction bighorn sheep adjusted timing and synchrony of parturition to environmental conditions of their release site. A slow adjustment of these life-history characteristics by females on Mount Timpanogos possibly contributed to lower survival of young to their 1st winter during 2001–2002 and 2004, which could have impeded establishment of those mammals in that study area.