No abstract

Electrocution by power lines is one of the main causes of non-natural mortality in birds of prey. In an area in central Spain, we surveyed 6304 pylons from 333 power lines to determine electrocution rates, environmental and design factors that may influence electrocution and the efficacy of mitigation measures used to minimise electrocution cases. A total of 952 electrocuted raptors, representing 14 different species, were observed. Electrocuted raptors were concentrated in certain areas and the environmental factors associated with increased electrocution events were: greater numbers of prey animals; greater vegetation cover; and shorter distance to roads. The structural elements associated with electrocutions were shorter strings of insulators, one or more phases over the crossarm, cross-shaped design and pylon function. Of the 952 carcasses found, 148 were eagles, including golden eagle (Aquila chrysaetos), Spanish imperial eagle (Aquila adalberti) and Bonelli's eagle (Aquila fasciata). Electrocuted eagles were clustered in smaller areas than other electrocuted raptors. The factors associated with increased eagle electrocution events were: pylons function, shorter strings of insulators, higher slopes surrounding the pylon, and more numerous potential prey animals. Pylons with increased string of insulators had lower raptor electrocution rates than unimproved pylons, although this technique was unsuccessful for eagles. Pylons with cable insulation showed higher electrocution rates than unimproved pylons, both for raptors and eagles, despite this is the most widely used and recommended mitigation measure in several countries. To optimize the application of mitigation measures, our results recommend the substitution of pin-type insulators to suspended ones and elongating the strings of insulators.

The analysis of 267 records of non-natural mortality of the Spanish imperial eagle Aquila adalberti over a 16-year period (1989-2004) shows an annual rate of 15.1 individuals found dead per year and that electrocution (47.7%) and poisoning (30.7%) were the most frequent causes of mortality. Most cases (91.7%) were of human origin, and of those 92.3% were accidental. Just over half (50.2%) were related to the transmission of electricity and human activity (collisions and electrocution), and 40.7% related to game practices and livestock protection (control of predators). No differences between sexes were found but subadults were electrocuted more frequently than expected whilst adults were poisoned more frequently. In breeding areas poison was the most frequent cause of mortality, whereas electrocution was the most common cause of death in dispersal areas. Poisoning occurred more frequently than expected in the Northern and Southern regions compared to the West-Central region. Electrocution was significantly more frequent in the West-Central region, and less common in the Southern region. The increase in electrocutions over the last few years is associated with previous non-permanent corrections on electricity power lines, whilst the increase in the cases of poisoning appears to be associated with the use of illegal poison in predator control by small game practices and for livestock protection. Permanent corrections in power lines and more research and awareness effort in the small game sector are recommended to reduce human-induced mortality in this Vulnerable species.

We studied (14 500 h of field observations during 20 breeding attempts by 10 pairs) the effects of human activities on the behaviour of breeding Spanish imperial eagles. The probability that human activities around nest sites provoked a flight reaction varied significantly among territories and among types of activity, and increased when the distance between the activity and the nest site decreased, and increased when the number of people involved in each intrusion was higher. Pedestrian activities (mainly by hunters, campers and ecotourists) caused more flight reactions than vehicles. Overall, the probability of a reaction increased sharply when activities occurred at less than 450 m from the nest, but was negligible if they occurred at 800 m. Reaction probability was lower in territories with higher intrusion frequencies (which suggests that some habituation occurs), where the nest was not visible from the tracks, and in less 'plain' or 'accessible' territories. Hatching rate was affected negatively by the frequency of human activities. Our results suggest that the critical inner buffer zone around Spanish imperial eagle nests should be established at a minimum radius of 500 m, and the vulnerable zones at a minimum of 800 m, bearing in mind the physiography of the terrain and the visibility of the nests. Finally, in future studies of nest-site selection with this species, it would be advisable to use a variable that quantifies (through field observations) human disturbance frequency.

The role that apex predators play in ecosystem functioning, disease regulation and biodiversity maintenance is increasingly acknowledged. However, the positive impacts of their presence in terrestrial ecosystems, particularly in human-dominated landscapes, remain controversial. Limited experimental insights regarding the consequences of apex predator recoveries may be behind such controversy and may also impact on the social acceptability towards the recovery of these species. Using a quasi-experimental design and state-of-the-art density estimates, we show that the restoration of an apex predator caused a short term, local reduction of mesopredator abundances, with resonating positive impacts on lower trophic levels. Iberian lynx Lynx pardinus reintroduction reduced the abundance of mesocarnivores such as red foxes Vulpes vulpes and Egyptian mongooses Herpestes ichneumon by ca. 80% and contributed to the recovery of small game of high socioeconomic value (European rabbits Oryctolagus cuniculus and red-legged partridges Alectoris rufa). The observed mesopredator reduction resulted in an estimated 55.6% less rabbit consumption for the entire carnivore guild studied. Our findings have important implications for the social acceptability of Iberian lynx reintroductions, which crucially depend on the perception of private land owners and managers. Under certain circumstances, restoring apex predators may provide a sustainable and ethically acceptable way to reduce mesopredator abundances.