How important are red-legged partridge releases in the spread of potential pathogens?

Abstract

The red legged partridge is one of the most popular game bird species in Europe. More than three million farm red-legged partridges (Alectoris rufa) are said to be reared and restocked into the wild. Nonetheless real figures are probably higher. Releases and restocking operations usually result in a short-term increase of population densities that allow for subsequent high shooting pressure, but it is far from clear whether they actually enhance the wild stock. Also, sanitary problems may arise whether farm reared partridges introduce pathogens into the wild. This is so because farm condition may exposure, for example, to enteric bacteria, and birds may suffer increased stress during release operation and subsequent pathogen activation. A total of 285 cloacal swabs from hunted red-legged partridges were collected during the seasons from 2007 to 2011 from 8 hunting estates within the province of Ciudad Real (Castilla - La Mancha, Spain), among which the intensity of restocking operation differed, both in the proper estate and in the surrounding area. Restocking activity was characterized by using official statistics provided by the authorities. The cloacal swabs, were processed according to standard laboratory procedures for detection and isolation of Escherichia coli. Association of prevalence of E. coli in sampled estates to releases, in the estate or surrounding hunting estates were investigated using a generalised lineal model (GLM). Significant differences on the prevalence of E. coli were found between restocked (46%, 66 out of 143) and natural populations of red-legged partridges (11%, 16 out of 142) (χ2=40.627; d. f=1; p<0.001). GLM analysis showed an overall positive association of the release of farm-reared partridges and the E. coli prevalence observed in restocked and wild partridges, so that restocking-based intensive management strategies may convey a risk of increased of E. coli prevalence, probably by introduction of carriers into the wild. This research evidences that consequences of introducing farm-reared birds into hunting areas may result in negative effects not only for partridges in the related areas, but it could also affect hunting districts where releases are not carried out but that are in close contact to intensively managed hunting estates. The spread and the introduction of enteropathogens such as E. coli to the environment could suppose a potential source of contamination for wild partridges, especially at feeding points in the hunting estates, where cross-contamination between birds may be enhanced and increased because of the stress and adaptation to the new habitat. In order to assess and maintain the health status of wild and restocked partridge populations, it would be necessary to implement a controlled management of hunting estates where restocking is carried out combined with adequate sanitary procedures of partridges during farm-rearing in aviaries.