Evidence of the phenotypic expression of a lethal recessive allele under inbreeding in a wild population of conservation concern

Deleterious recessive alleles that are masked in outbred populations are predicted to be expressed in small, inbred populations, reducing both individual fitness and population viability. However, there are few definitive examples of phenotypic expression of lethal recessive alleles under inbreeding conditions in wild populations. Studies that demonstrate the action of such alleles, and infer their distribution and dynamics, are required to understand their potential impact on population viability and inform management responses.\ud The Scottish population of red-billed choughs (Pyrrhocorax pyrrhocorax), which currently totals