Sperm from elderly birds produces lower quality offspring than sperm from younger birds, a large study of captive houbara bustards (Chlamydotis undulata) reveals. This finding adds to a growing body of evidence suggesting that the function of vertebrate sperm declines with age.

Traits associated with reproductive competitiveness have been found to decline in aged males (such as rutting activity, social dominance, sexual signalling) and this is expected to result in reduced reproductive output. What is less often considered is the effect of male aging on reproductive success after insemination and on the quality of offspring produced due to the decline in viability of gametes.

Brian Preston and colleagues studied ten years of data from a large scale conservation programme in Eastern Morocco. Here, female bustards are artificially inseminated as part of a captive breeding programme, which means that parental influence is only achieved via gametes. The authors found that paternal aging reduced not only the likelihood that eggs will hatch, but also the rate at which chicks grow. Sperm from immature males, in contrast, produced the fastest growing offspring.

The authors also found that the size of the effect is on a par with that associated with maternal ageing and this is thought to be due to the slow build-up of random genetic mutations within the male germ cell line. The same mechanism may underlie similar findings in humans, where increased paternal age has been linked to adverse reproductive outcomes, though further research is needed to confirm this.