In my last post, I gave a brief review of some scientific studies that have demonstrated the poor success of penned bird stocking systems purported to dramatically increase quail and pheasant populations. In case you’re still not convinced that stocking penned birds is a waste of time and money, today we’ll discuss a few potential negative consequences of stocking.
Anytime animals are raised in high population densities, there is increased risk for disease outbreaks. While diseases can and do occur in wild populations, wild populations are often spread out enough that transmission is minimized, or the disease reduces the population to the point where transmission is less likely. But because penned birds are raised in artificially high densities, disease outbreaks are more likely. Therefore, breeders often medicate birds against these diseases. But routine medication can result in resistant strains of bacteria and viruses that might be unwittingly released into the wild population. Another possibility is that penned birds might be released at the start of a disease outbreak, before symptoms are fully manifested or before many birds have contracted it. In this case, it might fully erupt after release, thus threatening the health of released and wild birds as they later co-mingle.
Researchers at Mississippi State University (Evans et al. 2006) conducted a genetic assessment of wild, pen-reared, and F1 hybrid (first generation wild x penned cross) bobwhites. Besides finding that wild bobwhites had significantly higher survival rates than pen-reared birds, they found that genetic diversity, number of alleles, and allelic richness was highest in the wild birds and lowest in the pen-reared birds. F1 offspring demonstrated intermediate levels in all three categories. It is not known what the alleles missing in the penned and F1 birds represent, but a reduction in alleles and genetic diversity could have negative effects on bobwhite populations. While it is unlikely that pen-reared birds will even survive to breed, large releases might have a few birds that do survive and mate. This genetic dilution might, over time, have important implications for the survival of wild populations.
Given the overwhelming mountain of evidence that stocking rarely works, and some of the potential consequences for the few times that it might, I hope you’re convinced that the best use of your money and time lies in habitat management. Pen-raised gamebirds have a role in dog training and in the operation of hunt clubs and shooting preserves where hunting pressure is too high for wild populations to sustain. But in those instances, birds should be inspected to insure they are healthy and released shortly before the hunt. Managers expecting great population increases are likely to be pretty disappointed and several dollars poorer.