Assessing the effects of trapping on pest bird species at the country level

Abstract

Control to limit damage caused by undesirable organisms at the country level is a common management practice but its effects on the target populations are usually unknown. Monitoring consequences of control is however important to design and measure the efficacy of long-term management. Using data from the French Breeding Bird Survey and methodology that cope with detection bias, we studied the consequences of trapping on the age structure and spatial dynamics of the magpie (Pica pica), a bird considered as a pest species in France. Our results show that magpie occurrence in farmlands and semi-natural landscapes decreases with regional trapping intensity. Trapping increase the probability of populations becoming extinct locally, with less possibility of (re)colonising managed areas. Local extinction is likely the consequences of changes in the age structure of breeding populations which are composed of more immatures in intensively trapped areas. The effects of trapping are however mitigated in urban areas, which have become a refuge habitat for magpies.Trapping is a long established and very common practice in France. Although trapping has a successful impact on the magpie in countryside, it is recommended only if justified by conservation specific purposes. Non-lethal methods exist like reducing availability of human-related food resources, especially in urban environments. Monitoring the dynamics behind species occurrence is a useful approach to understand how control affects species distribution. This study illustrates the value of a national monitoring scheme in helping to understand trapping consequences.