Abstract
A decrease in the numbers of the Mallard (Anas platyrhynchos) has led to game-farming and the release of captive-bred Mallards for hunting purposes in many states, including the Czech Republic, frequently on a large scale. In this way, more than three million Mallards are released globally every year.
Captive animals are affected by different selection pressures and evolutionary processes than those living in the wild, that may lead to genetic and phenotypic divergence between these populations. Although greater attention of the scientific research to the possible risk of hybridization and introgression of released individuals with wild populations has been mainly focused on supplementations of endangered species, there is a growing interest in the issue of restocking recreationally hunted species.
Studies show that captive rearing has led to a loss of genetic diversity, as well as to morphological, physiological and behavioural differentiation in the farmed Mallard populations compared with wild populations. The divergence between these populations, despite the development in standardized conditions, suggests that these differences are genetically-determined.
The observed phenotypic divergence is thus not only a result of the phenotypic plasticity of these 3 SYLVIA 51 / 2015 traits. Therefore, restocking of Mallards poses a threat to the genetic identity and variability of wild populations and may potentially lead to phenotypic changes.
This paper reviews the scientific literature dealing with this issue and discusses possible measures and the importance of monitoring of Mallard supplementations.