Course:CONS200/2023WT2/Effects of transmission lines on raptors' migration

Effects of Transmission Lines on Raptors' Migration

Increases in global population have resulted in the expansion of electrical infrastructure, impacting the migratory patterns of raptors. Habitat fragmentation is a leading cause of biodiversity loss globally, as seen in the population degradation of raptors in many parts of the world. Behavioral responses to new infrastructure provides insight into the effect that infrastructure including electrical tranmission lines Transmission lines help transfer electricity through cables that have been suspended or run underground. These power-line grids are expanding throughout the world and have been known to cause the death of birds when making direct collisions. A study conducted in 2021 showed that power lines in a specific area could kill between 94 and 240 Steppe eagles, which is 0.3% of their population worldwide annually. The following wiki page will be dedicated to exploring the effects that transmission lines have on raptors’ migration.

Evidence of the core issue

A raptor stuck in an overhead power line. Photo by: David A. Scott

Causation of Raptor Deaths

It was observed that under transmission lines in Saudi Arabia along a stretch of 14.4 km, there were 52 carcasses found, of which 85% were Steppe Eagles. Further looking into the study it was found that the carcass encountered rate for Steppe Eagles was 2.3 ind./km. If these numbers were extrapolated over a four-month wintering period for Steppe Eagles, dangerous electricity infrastructure around the studied area may kill anywhere between 0.15% to 0.30% of the global Steppe Eagles population every winter. Due to there being similar infrastructure around many other areas of Saudi Arabia that were not included in this particular study, it was suggested that the existing dangerous infrastructure should be safeguarded. While newer designs should aim to be safer to avoid the continued mortality of migratory birds as a whole.  

In a different study conducted in Ontario, Canada traumatic deaths of raptors were commonly attributed to collisions with stationary objects. Included under the category of stationary objects are power lines however, these power lines only accounted for less than 10% of the collisions. however, electrocution was its own category, and when stationary collision deaths are coupled with deaths via electrocution, it has an effect on raptors in the area.

Power lines are said to be one of the major causes of death in birds in the African-Eurasian regions. In Morocco, there is no legislation around the prevention measures of electrocution, which poses a threat to large bird species, particularly storks and raptors. This study was conducted over 9 months where 65 raptor carcasses were found, this number does not account for the carcasses that were taken by scavengers. Meaning that the 65 raptors’ found is said to be the minimum estimate for casualties. Such a high mortality rate may have significant negative effects on resident and breeding species on a local scale, while also threatening wintering and dispersing species. High pray abundance is identified as an important parameter of the local raptor concentrations and a predictor of higher electrocution risk in the landscape. Changing the design of the pylons could significantly reduce the number of electrocution casualties however, this is an expensive endeavor, and as such areas should be prioritized based on their level of risk to raptors.

Impact of Habitat Fragmentation

Habitat Fragmentation is the leading cause of biodiversity loss in the Anthropocene era. Urbanization and the expansion of electrical infrastructure has impacted the migratory patterns and decline in raptor populations due to direct collisions. Raptor populations that are divided by power lines face the impacts of changes to their habitats and nesting sites, leaving them more susceptible to population decline. Essential upper trophic level species including scavengers and raptors are facing the threats of habitat fragmentation and ecosystem degradation more drastically due to their position as top predatory species.

Globally, raptors play a role in ecosystem dynamics and the human-nature dichotomy as they provide pest control and cultural services. Birds of prey are essential to control rodent populations in both urban and rural ecosystems.  The transformation of habitats and migratory paths of fauna such as raptors by humans is a major challenge. The expansion of electrical infrastructure The potential loss of landscape connectivity not only poses challenges for raptor populations directly, but causes changes to the predation of rodents controlled by raptors.

Raptors have been categorized as an “umbrella species” holding an integral role in ecosystem dynamics, providing provisioning, cultural resources, cultural symbols and agricultural pest control. The decline in predation by raptors increases the use of pesticides and rodenticides in agriculture, furthering the degradation caused by the decline of raptor species. Predators are more susceptible to human-induced environmental changes.

In Kenya, declines in vulture and eagle species were exacerbated by urbanization and the increase of electrical infrastructure. Due to their role as apex predators, raptors species are highly sensitive to changes in environment caused primarily by electrocution and habitat and migratory pattern degradation. Raptors are a keystone species that are integral to ecosystem functions and services which lower trophic levels also rely on. In order to mitigate the risk of raptor species extinction, urban planning and infrastructure construction will require careful consideration for the role of raptors within urban ecosystems.

Contributing Factors

The downfall of these large birds (raptors, eagles, condors etc.) ultimately started with the rise of infrastructure and population growth. One key example of this was seen in a study performed in Kenya, where road surveys documented the encounter rates of large eagle species and vultures, along with smaller species such as raptors. Over a 50-year period, there was a documented 76% decline in encounters of large species in unprotected areas and an 85% decline in smaller species within unprotected areas. The main cause of this severe decline is the ever-growing electrical infrastructure branching out from cities across the world. With the expansion rate of 5% a year, there appears to be no stop to the rising mortality rates of avifauna. There is a severe lack of action from government officials and scientists alike in this considerable area, regardless of the startling death rates seen across the world from electrocution, habitat fragmentation and powerline collision.

One contribution to the survival of these birds has been the growth of protected areas. In the same Kenyan study, it was found that, when in protected areas, the encounter rates of raptors rose by 104%.

Current Efforts and the Path Forward

Avian Flight Diverters

Avian Flight Diverters, by LineStar, installed onto a section of a power line. Photo by: LineStar.ca

While at first glance it may seem that these birds have no saving grace, there are many current efforts in the works. A recent emergence of new technology called Bird Flight Diverters (BFD) are installable on power lines to make them more visible to flying raptors. The installation of these would be costly over a wide area, however, it would significantly reduce the risk of collisions as well as be much more economically viable over the long run. It is much cheaper to install BFD's in comparison to fixing permanently damaged lines from the collisions. Additionally, this solution maintains the ethical standpoint of protecting bird hunts from indirect human intervention.

Insulated Power Lines

Similarly, but slightly more costly, is the concept of insulated power lines. Using bird safe designs such as insulated power lines eliminates the threat of electrocution which is the most common issue for predatory birds that attempt to perch on transmission structures. However, economic factors related to the mass insulation of power lines over large areas is heavily discussed. Relating to current capitalistic structures of the world and the widely accepted idea of saving every penny you can has affected all aspects in conservation, solutions as well as problems. Due to costly expenses such as hiring workers, gathering the right materials, and the amount of work they would have to do would be inefficient and ineffective. However, this would almost entirely eliminate the problem of the declining raptor population and the fail rate of their hunts.

Effects on Migration

Negative Effects on Migration

It has been seen that many birds change their migratory behaviour in response to environmental alterations. The mortality of these migratory birds is seen to be 2.4 to 3.5 times larger than that of sedentary birds. Of these mortalities, collisions with power lines were found to be the main cause of deaths from unnatural circumstances. These collisions occur more frequently in migration periods, and human-induced mortalities may be playing a factor in shaping new migratory patterns. Therefore, it may be said that the presence of power lines may be causing a reduction in overall migratory birds and the changing in patterns for many species of birds. Some raptor species are concentrated highly in some areas although they are generally low in population. As 40% of nocturnal raptor species have become endemic to a specific area, they have become more sensitive to effects on migration. For example, the Ridgeway's Hawk in endemic to a small region of the Dominican Republic, making the species highly at risk of changes in migration patterns. Low populations coupled with high, sometimes endemic, density creates an increased threat to biodiversity in raptor habitats. Changes to migration patterns, as the threat of human electrical infrastructure poses on raptor species, can hinder biodiversity, therefore decreasing the efficiency of ecosystem services.

Similarly, the Habitat Management Guides for Birds of Prey by Mayo Call (published October 1979) went into extreme detail on various factors that affect migratory patterns and overall habitat stability. The article stated that disturbing activities such as construction should one be permitted once predatory birds have migrated out of the area and have not yet returned to their location. Furthermore, the article states that conflicts may occur between various facilities (including powerlines) with roosting and feeding areas, causing birds of prey to abandon their traditional hunting grounds. This would subsequently force predatory birds to accommodate for this change, exposing them to the danger of both the power lines, as well as the risk of not finding a suitable location.

Conclusion

Global population expansion has direct effects on the abundance of raptor populations globally. Increasing energy infrastructure has caused fragmentation of habitats and migratory patterns, creating direct negative implications for raptor species and the ecosystems that they are a part of. The expansion of human-caused habitat fragmentation is a leading cause of biodiversity and therefore must be regarded as a major focus of conservation efforts around the globe. The impact of energy infrastructure proves to hinder the ability of ecosystems that rely on raptors as apex predators to perform ecosystem services such as waste recycling. The role that raptors play as tertiary consumers in the food chain makes them essential for ecosystem function, meaning that the changes to habitat and migration patterns caused by energy infrastructure could pose biodiversity degradation.

The grave impact that electrical transmission lines have on raptor populations is a global phenomenon. Not only do these structures present a physical barrier, leading to collisions and electrocutions, but they also contribute to habitat fragmentation and changes in migration patterns. In countries like Saudi Arabia, the United States, and Canada, studies have demonstrated that raptors in particular are at risk; notable percentages of raptor deaths are attributed to power line interactions, most commonly electrocution.

Despite the aforementioned statistics throughout the article, efforts to prevent/mitigate this crisis are underway. Innovations such as bird flight diverters, insulated power lines, and further habitat pre-cautiousness offer hope for reducing raptor deaths. However, economic considerations involved with these said ideas often slow their implementation into the field. Taking on these technologies, along with the establishment and enforcement of new wildlife policies, is critical to conserving raptor species.

For the future, it is of utmost importance to balance the need for electrical infrastructure development with the conservation of biodiversity. An approach involving extensive research, technology, policy, and community engagement is crucial. While expanding protected areas and enhancing existing ones can also help, evidenced by the numerous studies showing increased raptor encounters within the protected regions.

The protection of raptors is not just an act of conservation, but a necessary step to maintain a natural equilibrium in the environment. Each piece, regardless of how miniscule or grand it may be, is key in maintaining biodiversity; without a complex ecosystem filled with biodiversity, the global efforts of conservation will go out the window. Since humans have assumed the role of custodians of biodiversity, it is our obligation to ensure that our footprint and future does not come at the cost of the life that enriches our natural world.