Abstract

The goal of conservation breeding and reintroduction programs is to help re-establish or support declining populations in the wild, but there are challenges to successful implementation. Captive and wild environments may differ in ways that impact animals’ development or behaviour. One way organisms may respond to their environment is by adjusting their offspring sex ratios to maximize their own fitness. Sex ratio has been observed to vary in response to several cues, including parental condition and food availability. In conservation breeding programs, where individuals are sheltered and provided with abundant food, sex ratio adjustment could bias offspring sex ratios. Here, we investigate whether there is evidence of sex-ratio adjustment in a Western burrowing owl (Athene cunicularia hypugeae Bonaparte, 1825) conservation breeding program, using data on over 300 broods collected from 3 facilities across 30 years. We find that the average and variance of brood sex ratio do not differ from that expected under Mendelian segregation. We did not find evidence that sex ratio adjustment is occurring in the Western burrowing owl breeding program; either because they are not receiving cues to do so in the ex-situ environment, or because this species does not facultatively adjust sex ratio.