Interview Pascual López about power lines and raptors in Spain

Date of the interview: 22 March 2011

In this interview, raptor researcher Pascual López from the University of Valencia talks about power lines and raptors in Spain. Power lines are a serious threat to many raptors around the world and in Spain many birds are killed by electrocution or collision with power lines. This is one of the main causes of death for endangered species like the Spanish Imperial Eagle or the Bonelli's Eagle but progess is being made in Spain to reduce the mortality.
Pascual's research is primarily focused on population ecology of birds, with special emphasis on conservation of endangered raptors. See his website (link down below the interview) to learn more about this research and publications.

Markus Jais: What exactly is electrocution when it comes to raptors? How do birds get killed by electrocution?
Pascual López: Electrocution of birds has been reported to be one of the most important mortality factors worldwide. Electrocution mainly occurs when birds perch on pylons with some electrical components uncovered. When birds touch the cables, or touch one of the cables and the pylon, they close the circuit and the current circulates across them, killing the animal consequently. The mortality caused by electrocution becomes especially important when it comes to raptors because of their behaviour. Raptors usually perch on pylons which are elevated over the terrain. This facilitates searching for prey from these look-out posts. Pylons are particularly used in agricultural landscapes and open areas, where the human activity has caused the clearance of the natural vegetation and even deforestation.

Pascual López

Pascual López © Clara García

Markus Jais: Collision with power lines is also a serious problem for some species. How serious is this threat for raptors in Spain?
Pascual López: Collision with high tension power lines (>110 kV) is known to be also one of the most important causes of mortality for endangered species of raptors. For example, it has been reported that collision with power lines represents the third highest cause of mortality for the Bonelli’s eagle. However, although the collision with power lines can affect all species of birds, there are some species which are more prone to die because of collision, mainly due to their flight behaviour. Species with faster flight speed such as pigeons or ducks, gregarious species with low maneuverability such as cranes, flamingos, capercaillies and steppe-land birds (bustards, sandgrouses, etc) are particularly prone to collision with power lines. There is some lack of information about collision of raptors with power lines, but for some species for which extensive research has been done (e.g. the bearded vulture) it has been reported to be also an important source of non-natural mortality. Taking into account that there are estimated to be 65 million km of medium–high voltage power lines presently in use around the world, there is still room for investigation and for implementation of mitigation measures.

Markus Jais: Two of the most affected species are the Spanish Imperial Eagle and the Bonelli’s Eagles, both rare and threatened species in Spain. How many are killed each year in Spain through electrocution and collision?
Pascual López: Mortality caused by electrocution due to poorly-designed pylons and power lines can seriously affect avian species particularly when population size of the affected species is low or its distribution is limited. This is particularly the case of the Spanish Imperial eagle and the Bonelli’s eagle. In a recent study we have analyzed mortality data of Spanish Imperial eagle in Andalusia (southern Spain) of the last 35 years. Since 1974, a total of 158 Spanish Imperial eagles have been recorded dead in Andalusia, 101 of them (63.92%) inside Doñana National Park. Electrocution was the most frequent cause of death accounting for 39.87% of the total mortality events. Since 1974 when the first death by electrocution was recorded, 37 Spanish Imperial eagles have been found electrocuted in Doñana (36.63% of the mortality cases) and 26 cases in Andalusia (41.94% of the records). In the case of the Bonelli’s eagle, there is not a compiled database, but according to the available literature, more than 200 eagles have been recorded dead by electrocution in the last 10 years. This mortality cause has been particularly accentuated in some Spanish regions as Catalonia, where electrocution accounted for 65% of the mortality causes during the nineties. In addition, mortality caused by electrocution also represents the most important mortality factor at juvenile dispersal areas, which are mainly located in inner and central Spain. Currently, there are several projects carried out by NGOs, regional governments and the Spanish Ministry of the Environment aimed at mitigating mortality of raptors. These projects include measures to avoid bird electrocution principally. In addition, there has been an increasing pressure to legally require that efforts to mitigate avian electrocution are made. As a consequence, regional and national laws were approved with regard to avian electrocution.

Egyptian Vultures

Egyptian Vultures © Alberto_Martin

Markus Jais: Are young more often killed than adults and females more often than males?
Pascual López: That’s right. It has been reported in the literature that inexperienced immature and subadult birds as well as females are more prone to electrocution than other birds. This is largely due to differences in bird’s behaviour in relation to age. Inexperienced birds are usually displaced to areas where human influence is higher (i.e. dispersal areas) and therefore the probability of electrocution is also higher. In relation to sex, it’s well known that females are larger than males in species with reversed size dimorphism such as some raptors. Several studies have shown a strong sex-biased distribution of mortality towards female birds. For example, in the case of the Spanish Imperial eagle females formed 78,12 % of eagles killed on power lines. Similar results have been reported for other species of raptors such as the Bonelli’s eagle, Booted eagle, Golden eagle and Goshawk.

Markus Jais: What is the effect of that mortality on the population dynamics of those two eagle species?
Pascual López: The importance of human-induced mortality has a strong influence in the context of population dynamics. The effect of mortality (either adult or juvenile mortality) plays a key role in determining demographic trend of any given species. Demographic parameters (i.e. mortality, breeding performance,…) are not independent of one another and interact between them. This should be taken into account when endangered small populations are analyzed, as in the case of the Spanish Imperial eagle. In fact, our results have shown that in the particular case of long-lived spatially structured populations (such as the Bonelli’s eagle and the Spanish Imperial eagle), pre-adult and adult mortality play a key role in influencing population persistence. Therefore conservation measures should be focused on mitigating detrimental effects on these parameters. In the case of Spanish Imperial eagle, adult survival is higher than pre-adult and floater survival, and hence small electrocution rate of adult eagles leads to more severe consequences on population dynamics than the death of non-breeding individuals. On the contrary, in the case of Bonelli’s eagle, our results show that pre-adult mortality plays the key role in determining the overall population trend. This reinforces the idea that to ensure the long-term persistence of the species in Spain, management actions should aim at minimizing pre-adult mortality. These include locating and protecting the juvenile dispersal areas, minimizing the risk of electrocution in power lines, and preventing human persecution.

Markus Jais: The population of the Spanish Imperial Eagle has increased significantly during the last decades to more than 250 in 2008 despite many eagles being killed through electrocution. How you think the population would have developed if there weren’t any death caused by electrocution?
Pascual López: Fortunately, the population of Spanish imperial eagle has increased in Spain in the last decades. At the national level, after the correction of power lines, the population of Spanish Imperial eagle has increased from 103 pairs recorded in 1983 to 286 pairs in 2010. In the case of Andalusia, the population has raised from 22 pairs recorded in early seventies to 61 pairs recorded in 2010, with this population currently representing nearly 20% of the world population of the species. It should be taken into account that, for example, in 1982, in just 100 km of power lines, more than 2000 birds were recorded dead and 400 of them were raptors. However, after applying evidence-based mitigation measures, there has been a positive change in the demographic trend of the Spanish Imperial eagle, shifting the main causes of mortality before and after the approval of mandatory regulation against bird electrocution. Therefore, it has been demonstrated that solving bird electrocution is an affordable problem if political interest is shown and financial investment is made. The combination of an adequate spatial planning with a sustainable development of human infrastructures will contribute positively to the conservation of the Spanish Imperial eagle and may underpin population growth and range expansion, with positive side effects on other endangered species.

Markus Jais: How do you think the population of the Bonelli’s Eagle in Spain would be without electrocution?
Pascual López: I don’t like to make speculations. Nonetheless, I’m completely sure that if electrocution problems would have been avoided, the current population of Bonelli’s eagle would be higher than that recorded nowadays. Taking into account that Bonelli’s eagle’s pre-adult mortality is around 80-90% and adult mortality ranges from 3% to 16%, a theoretical decrease of mortality would give a better picture of the current situation of the species in Spain. For example, in a demographic analysis that we did for some Spanish subpopulations of Bonelli’s eagle, our results showed that specifically, a 20% decrease in pre-adult mortality during the first two years of life was enough for the stabilization of the entire Spanish population. This clearly shows that conservation strategies for the species in Spain should seek to ensure that pre-adult mortality decreases, and this mainly includes measures aimed at identifying dangerous lines and poles and modifying pole design. Thus, locating and protecting the areas used by juveniles Bonelli’s eagles as temporary settlements, and putting forward conservation measures aimed at diminishing electrocution and shooting there, are likely to result in sensible improvements on the species’ status in Spain.

Spanish Imperial Eagles on corrected pylon

Spanish Imperial Eagles on corrected pylon

Markus Jais: In some countries only the power lines and pylons the areas close to nests are made safe. Isn’t this completely ignoring the dispersing juvenile birds?
Pascual López: That’s right. Undoubtedly, it is an error to focus conservation actions in just one part of the entire population (in this case the breeding portion of the population). Juvenile dispersing birds as well as floaters (i.e. mature individuals that are not occupying breeding territories) are very important from the conservation point of view. As I previously said, demographic studies show that juveniles and floaters are key in determining the overall population trend of any given species. Therefore, conservation actions should also be focused at correcting dangerous pylons at juvenile dispersal areas as well as at wintering areas, in the case of migratory species. Measures aimed at protecting just one part of the population are clearly ineffective and may lead to a waste of financial resources that could be applied more efficiently if juvenile birds and floaters would be taken into account.

Markus Jais: What other raptor species are threatened by electrocution and collision in Spain?
Pascual López: This is not an exhaustive list, but several studies have reported the recovery of electrocuted birds of several species of raptors such as the Osprey, Black kite, Red kite, Egyptian vulture, Golden eagle, Short-toed eagle, Booted eagle, Eurasian Griffon vultures, Common buzzard, Goshawk, Kestrels, harriers and several species of owls especially including the Eurasian Eagle owl and the Barn owl.

Markus Jais: What poles are the most dangerous ones?
Pascual López: Raptor electrocution mainly occurs at low-tension power lines (16–45 kV). Pin-type poles placed in natural habitats are the most dangerous ones. For example, our results showed that pin-type poles in the natural habitat accounted for 26.3% of the mortality of Spanish Imperial eagles, but only 6.7% of poles in natural habitat are of this type. One of our main recommendations in solving the electrocution problem is to concentrate on the most dangerous pole designs. In the case of Andalusia, mitigation measures aimed to ameliorate the impact of power lines were implemented in those poles for which were reported an elevated risk of electrocution. These included the construction of new pylons with suspended insulators, avoiding the use of pylons with an exposed loop of wire above the insulator, and ensuring that new power lines were located away from both breeding areas and areas of temporary settlement of juvenile eagles, as abovementioned. In the case of existing power lines measures were focused on correcting dangerous pylons by replacing exposed rigid insulators with suspended ones and installing protective systems on the pylons to prevent birds from coming into contact with wires.

Markus Jais: The best solution would probably be to put the power lines underground. Is this possible in the many rocky areas of Spain and is it done in some places?
Pascual López: That’s completely right. The best solution to avoid electrocution is to put the power lines underground. The main advantage is that it avoids the risk of electrocution completely and, furthermore, the impact on the landscape is greatly reduced. On the contrary, the main shortcoming is that this requires an important financial investment. From my personal point of view I consider that putting the power lines underground should be taken into account whenever possible. This is particularly important when it affects areas of special conservation interest such as natural and national parks and Natura 2000 network areas. In these cases it should be mandatory. In Spain, it is being done in some places (i.e. at wind farms developments), but work is still needed.

Young Spanish Imperial Eagle on Pylon

Young Spanish Imperial Eagle on pylon

Markus Jais: What can be done to make pylons and power lines safe for raptors and what is currently being done in Spain?
Pascual López: Firstly, mitigation measures should include the identification of mortality hotspots. Then, it would be desirable to develop predictive cartography and prospective modeling of risky areas. Next, both proactive actions and reactive measures should be undertaken. The former would include making safe dangerous pylons before mortalities occur, whereas the latter would include making safe dangerous pylons after mortalities were recorded. Fortunately, electrocution risk does not take place randomly, but few pylons account for most electrocutions and hence, mitigation is feasible. Our main goal as scientist as well as conservation practitioners should be to find out the most dangerous pylons and then to focus the limited financial resources available on correcting these dangerous poles. For example, since 1992 until 2009 a total of 6560 dangerous pylons were made safe along 1446 km of power lines in Andalusia (in southern Spain). The total budget for these measures amounted 2.624.000€ (an average of 400€ per corrected pole). The Spanish Imperial eagle population in Andalusia has increased from 31 to 60 pairs in the same period. This figure represents slightly over half of the total investment in conservation of the species for this period. Taking into account the high budgets assigned to the construction of new power lines and alternative power sources (e.g. wind farms, solar panel arrays), it demonstrates that solving bird electrocution is an affordable problem if political interest is shown and financial investment is made. Furthermore, other avian species can be benefited from these measures.

Markus Jais: What more should be done to reduce the mortality of raptors in Spain in the coming years?
Pascual López: Future research should be focused on the development of new high-efficiency, low-cost devices that reduce electrocution risk of distribution power lines. These mechanisms should be easy to install. They should allow birds to perch and nest while protecting the lines to ensure that power supply is not disrupted due to bird electrocution events or short-circuiting by nest material. In addition, conservation actions should include adequate spatial planning, avoiding the placement of power lines in areas of special conservation interest. The combination of an adequate spatial planning with a sustainable development of human infrastructures will contribute positively to the conservation of raptors in Spain and may underpin population growth and range expansion of endangered species in our country. Furthermore, joint actions at every single one regional administration and the effective application of the current international, national and regional legislation would be desirable.

Markus Jais: How do you see the future of the Spanish Imperial Eagle and the Bonelli’s Eagle in Spain in regard to electrocution and collision?
Pascual López: I’m reasonably optimistic with regard to the future of raptors in Spain. In particular, in relation to the future of the Spanish Imperial eagle there is a general agreement on that the situation has improved much. The population has clearly increased in the last decades and the current challenge is to keep the positive trend in the future. With regards to the Bonelli’s eagle, the current status is somewhat different. Whereas some populations located in the southern and eastern regions seem to be increasing or stable, populations from the central plateau and northern Spain seem to be decreasing. There are also differences in the main causes of mortality among regions and age classes. Thus, whereas non-breeding individuals mostly die because of electrocution, adults are mainly the victims of persecution. Therefore, measures aimed at reducing electrocution and collision with power lines are of the utmost importance in order to ensure the long-term persistence of the species in Spain.

Markus Jais: How long have you been studying raptors and their conservation and what was your most amazing experience with those birds?
Pascual López: I’m currently 30 years old. I have been studying raptors since I was young, but “professionally” I started studying raptors when I was at the first courses of the University. I have several amazing experiences with raptors and I cannot clearly select a particular one. The excitement of finding a new breeding pair is very amazing; I have also had several amazing experiences when trying to capture different species of raptors such as Egyptian vultures and Eleonora’s falcons for the first time to fit them satellite-tracking devices. The results of satellite-tracking projects are quite amazing as well, for example when we realized that Eleonora’s falcons migrated across inland Africa and not along the Mediterranean Sea, as suggested by the literature.

Markus Jais: Pascual, thank you very much for the interview.

More information:

López-López P, Ferrer M, Madero A, Casado E, McGrady M (2011) Solving Man-Induced Large-Scale Conservation Problems: The Spanish Imperial Eagle and Power Lines. PLoS ONE 6(3): e17196. doi:10.1371/journal.pone.0017196.
This paper is available at:

Many other interesting papers about various raptor species inclunding Bonelli's Eagle, Golden Eagle, Spanish Imperial Eagle, Egyptian Vulture or Eleonora's Falcon are available at Pascual's personal website. Make sure to have a look: