Abstract
Wild birds and their habitats are an important part of the natural environment. Over 450 birds have been recorded in Ireland. Ireland is important for migrating birds with large numbers of birds such as waterfowl and waders spending the winter in Ireland. Summer migrants such as swallows and terns are also a feature of Ireland’s bird life.
This report is an independent, evidence-based study undertaken by experts in bird ecology. The research examines the effects of existing high voltage transmission projects at a number of sites on bird activity and behaviour.
The purpose of this study has been:
- To determine the effects of existing high voltage transmission infrastructure on bird activity in Ireland
- To provide a factual basis for the development of bird specific recommendations and guidelines for electricity transmission projects
The routing of transmission projects is a complex process. It requires a balance between a number of issues, including EirGrid’s obligations to ensure a safe and secure transmission grid, land use constraints, cost, engineering and other technical requirements. Impacts on the natural environment must also be considered. Transmission lines have the potential to impact on birds and routing of new lines must take this into account.
This study included a literature review of existing information and a field survey at sites around Ireland. The aim of the study is to find out if, and how, transmission powerlines affect birds in Ireland.
Published information from around the world has shown that certain birds are more at risk of collision with transmission lines than others. Large species such as swans, geese, and cranes are most at risk. Bird species considered ‘poor fliers’ such as grouse, pheasant, and rails are also at risk of collision. Certain factors such as time spent in flight, territorial displays, foraging flights or night flights can increase collision risk for birds including waders and raptors where overhead lines are present. Local conditions such as landscape and weather conditions can also influence the risk of collision.
The thin wire at the top of powerlines is widely reported as the main cause of bird collisions. Collisions with powerlines are considered to be rare events. Most studies conclude that mortality from collisions is unlikely to affect bird populations. However, where rare or protected species occur, impacts could be significant.
Measures to reduce bird collisions include careful line route assessments and the marking of lines to make them more visible to birds. Research shows positive results from marking lines, with reductions in bird deaths of 50% or more. The location for marked sections of transmission line is determined by survey and analysis of bird movements. Monitoring the effectiveness of the line marking is recommended.
The risk of electrocution on the transmission system is low. This is due to the wide spacing between live elements on the transmission lines and support structures.
The possible impacts of transmission line construction and electromagnetic fields (EMFs) are also investigated. Construction activities may cause temporary disturbance or permanent displacement to birds.
An important part of this study included a survey of collision risk. This involved a widespread field study in 2012/2013. This study examined a number of high risk sit es (5) for birds, and a sample of low risk (54) or control sites on the existing transmission system. Searches for dead birds were carried out at all sites.
A targeted survey was undertaken in 2014 at three high risk sites. This survey also collected information on flight activity of target species. Target species included swans, geese, ducks, gulls, herons, raptors, waders, and cormorant.
Results of the surveys were broadly in line with collision estimates published in the scientific literature. Results from high risk sites showed estimated collision rates of 0 to 179 birds per kilometre per year. This result does not take account of possible bias such as scavenger removal of dead birds by fox for example. The species recorded most frequently as collision victims at high and low risk sites included crow and pigeon species. Small numbers of gulls, waders, ducks, and passerines were also recorded. Grey Heron was recorded at wetland sites.
The flight activity survey provided new information on bird responses to transmission lines. No collisions were observed, however some avoidance behaviour was noted. At all sites, the majority of birds flew above the powerlines. The exception was at the 400 kV site (with the tallest pylons), where a third of all birds flew beneath the wires. Very few birds crossed powerlines at or near to pylons.
This study provides data and results which will inform the development of bird specific recommendations and guidelines for transmission projects in Ireland. The preparation of guidelines will ensure a consistent approach to ecology, including birds, at all stages of the development of transmission projects.