Inferring ecological mechanisms from hunting bag data in wildlife management: a reply to Blanco-Aguiar et al. (2012)

In a previous study, we suggested that hyperpredation by shared predators on red-legged partridges (Alectoris rufa), once a parasite (rabbit haemorrhagic disease, RHD) had decimated populations of rabbit (Oryctolagus cuniculus), the primary prey for most of the Mediterranean predators, was a major force driving partridge population dynamics in Spain years ago (Moleón et al., PLoS One 3:e2307, 2008). Recently, however, Blanco-Aguiar et al. (Eur J Wildl Res 58:433–439, 2012) have asserted that this conclusion is poorly evidence-based and can subsequently promote raptor persecution by hunters. In response to Blanco-Aguiar and colleagues, here we provide complementary insights that favour our earlier hypothesis. After explaining several key concepts of the hyperpredation process, we use additional data and analyses to show that (1) a synchronised regime shift (i.e. a step, abrupt change in population size) to significantly lower population levels in both the rabbit and partridge populations took place coinciding with the RHD outbreak; (2) rabbit and partridge population dynamics were highly synchronised after the RHD outbreak, but not before; (3) an enhanced spatial autocorrelation at all the spatial scales emerged after RHD for partridge populations; and (4) the main shared predators’ diet patterns were consistent with the hypothesis of enhanced predation pressure as a plausible mechanism behind the observed partridge dynamics. We support the idea that hunting bag data may be useful to infer realistic population dynamics and the ecological mechanisms explaining them, provided that (1) they are corrected by the number of hunting licenses; (2) appropriate statistical tools are employed; and (3) methodological constraints are adequately taken into account. Finally, we argue that the opinion of Blanco-Aguiar and colleagues that our original results can lead to raptor persecution is a misinterpretation of our study. In this sense, we make an appeal for the importance of accurately differentiating between the ultimate (e.g. infectious diseases favoured by humans) and the proximate (e.g. enhanced predation pressure) causes of the decline in prey of economic interest (e.g. game species) in order to avoid unnecessary, unfounded or presumed conflicts with lobbies of conservation concern (e.g. hunters).