While you may not fancy running into one in a dark alley, this striking bird (Bonelli’s eagle, pictured right) could use our help. Despite their wide global range, Bonelli’s eagle abundances in the Iberian Peninsula suffered a major decline in the 1980s and several populations are still declining. In particular jeopardy are those in northern Portugal and Spain, where the species is now considered endangered. The majority of eagle mortalities are due to anthropogenic impacts, whether directly or indirectly (e.g. electrocution from power lines), so it is not unrealistic to presume that without human interference these eagles would not be in such a plight.
In order for us to most efficiently protect the threatened populations of Bonelli’s eagle, it’s important to know where exactly we should focus our conservation methods. Like many researchers before them, Alvaro Soutullo and his team modelled declining sub-populations of Bonelli’s eagle in order to test the probable effects of conservation methods that could be undertaken to try and safeguard these Spanish birds of prey.
So what makes this new research so important? Previous studies have all regarded sub-populations as isolated, whereas this study took into account the large amount of movement between populations that occurs when young eagles disperse. The mortality of these juvenile dispersers was found to be the main driver of falls in abundance. Decreasing pre-adult mortality by just 20% was enough to counter the declines and stabilise the model populations. These novel results indicate that the most effective management strategy for endangered Bonelli’s eagle populations is to focus conservation efforts on decreasing juvenile mortality rates.
This strategy should prove to be much more efficient than actions focusing on adult eagles, as extensive research on minimising raptor electrocution already exists and efforts can be targeted to areas known to be used by juveniles. However conservation measures often work most effectively when more than one strategy is employed, so ideally efforts to minimise adult mortality should not be abandoned. Reducing juvenile mortality will make the biggest difference, but both of these management actions working in conjunction with each other will provide the best possible outcome for the endangered populations of Bonelli’s eagle.
Original article: Soutulloa A, Lo’pez-Lo’peza P & Uriosa V. Incorporating spatial structure and stochasticity
in endangered Bonelli’s eagle’s population models: Implications for conservation and management. Biological Conservation 141: 1013-1020.