The status and hunting of European turtle-dove (streptopelia turtur) in Spain

Resumen

The European Turtle-dove (Streptopelia turtur) is a migratory species classified as vulnerable suffering strong population declines in Western Europe during the last decades. This species is also considered as a game species and its management and conservation is a double challenge. On the one hand, understanding the causes of the decline is essential to achieve the species recovery. On the other hand, these causes may be occurring in one area but affecting populations somewhere else due to the migratory characteristics. Designing effective management strategies imply incorporating the idiosyncrasy of the species along with all the stakeholders involved in the populations included in the same flyway. This thesis is focused in the relationship between European Turtle-dove population decline in Spain and two potential drivers: land use and hunting. The estimation of population abundance trends is essential to assess the conservation status of a species. For this purpose, we analysed the population trend using citizen science data from the monitoring program SACRE (SEO/Birdlife) using models that allow to correct for the unequal spatial sampling. We describe that Spanish turtle dove population has suffered a 37% decline between 1996 to 2018, which equates to an average 2% loss per annum. Moreover, we identified spatial variation in the species habitat favourability, which is explained more by habitat than by topo-climatic variables. We analyse for the first time the relationship between trends and land uses, observing a steeper decline more associated to arboreal than agricultural habitats, highlighting the importance of arboreal habitat and its management for the conservation of the species. In other hand, the capacity of an animal population to sustain harvest should be estimated to avoid overexploitation. In this thesis, we evaluated if current hunting levels in Western Europe are sustainable or not using a demographic invariant model. We conclude that current hunting levels duplicate the harvestable population fraction under all suitably conservative scenarios. Thus, current levels of hunting along the western flyway are unlikely to be sustainable. Being turtle dove a migratory species, it is important evaluate how hunting in one geographical region is likely to affect breeding populations in other areas. For this reason, another objective of this thesis was to evaluate the composition of birds harvested in Spain with respect to their breeding origin using stable isotopes. Unfortunately, our results in this respect lead us to conclude that it may not be possible to use this method to reliable infer breeding origins; therefore, a precautionary approach should be taken and assume that hunting in Spain has the potential to affect all populations that breed further north. To achieve an adequate species management and assure hunting sustainability it is fundamental to provide updated, reliable and easily accessible harvest data that allow to assess science-based the efficiency of hunting regulations. We evaluated the reliability of the official harvest data, and the efficiency of hunting regulations (daily quota, total hunting days and, date of the beginning of the hunting season) applied until 2017 to decrease and control turtle dove hunting. We find a strong mismatch (mainly at the beginning of the study period) between accessible information of annual harvest in Spain as reported by the national ministry and the provincial and regional authorities, and several sources of bias. As a result, we find that official harvest data are underestimated; correcting those biases, we derived a minimum conservative estimate of the total annual Spanish harvest. We found that current variation in the three regulatory measures analysed (daily hunter quotas, modifications of the start and length of the hunting season) had no observable effect on provincial annual take. Lastly, we described hunting patterns at smaller scales (hunting estate level or hunting event) as well as other indicators (age ratio of hunting bags or the importance of birds shot but not retrieved as an additional source of hunting mortality, or ‘crippling loses’) to improve the efficiency in hunting regulations measures. We show that the number of turtle doves shot is higher when hunting is implemented from fixed positions than walked-up shooting, and estate-level annual harvest increases with hunter density, gamekeeper density and number of daily wages. This suggests that turtle dove harvest is more related to socioeconomic aspects than to the measures directly regulated by policy or the species abundance. We also determine that the age ratio of birds shot is unbalances, with the proportion of juveniles shot being higher than that of adults during the whole hunting season but particularly at the beginning of the hunting season (68%). Additionally, our results show that the number of turtle doves shot but not retrieved reaches on average 10%, which suggests that approximately 80 000-100 000 turtle doves may be shot annually in Spain but excluded from harvest statistics. These results could have important implications for the demographic models and for future adaptive harvest management of this species and may be integrated in the tools used by the managers and policy-makers to improve the species management and conservation, besides being used as an example of sustainable management of a migratory species in the future.