Bird migration along power lines

There is an intrinsic relationship between the electricity grid and the natural world.

The activities of grid operators like Terna require careful analysis of the issues connected to respect for the environment and biodiversity, both in the construction phase and live use.

Depending on the habitat they cross, power lines can indeed represent a potential risk for birds, which could crash into conductors.

Faced with this and other similar problems, starting in 2001, Terna began to install “deterrents”, spiral devices that make power lines more visible to migratory birds. On Italian pylons, there are currently 14,728 deterrents on 66 lines, 266 km long, with an average of 850 new deterrents installed every year.

The maximum attention is paid to biodiversity when high-voltage lines cross protected areas, that is national and regional parks, national and regional reserves, Sites of Community Importance (SCIs) and Special Protection Areas (SPAs). Because 10% of Terna’s electricity grid (around 6,024 km) crosses protected areas, it is easy to understand how the commitment to grid development, management and maintenance must go hand in hand with respect for nature.

A prime example of this is the monitoring carried out thanks to ornithologists and to the radars mounted along the “Sorgente-Rizziconi” power line which connects Sicily to Calabria.

In fact, the line’s route is affected by the intense migratory flow of a wide variety of birds of prey, as well as others.

Terna’s analysis (thanks to the support of twelve ornithologists from the Ornis Italica association) has not only shown that there have been no collisions among the more than 100,000 passings of birds of prey over the Strait, but has also facilitated the collection of a large amount of data which is crucial to migration research, and which Terna has decided to make available for free.

What does the data tell us? There are five major species (or which have been sighted most often): among the birds of prey are the European honey buzzard and the Western marsh harrier, and among the diurnal migrants are the swallow, the common house martin and the European bee-eater.

The monitoring lasted three years and saw a total number of 115,000 overflights during the migration periods, 70,000 during the spring (15 March / 31 May) and 45,000 during the autumn (15 August / 30 September).

However, a closer look reveals that the species sighted change based on the observation point. Not counting the ever-present European honey buzzard (which accounts for more than 60% of the sightings), the most sighted species in Calabria, at about 1,000 meters high, are, among birds of prey, the Western marsh harrier, the black kite and the kestrel, and among other birds, the European bee-eater.

The Serro observation point in Sicily, about 280 meters above sea level, is the preferred passage for passerines (swallows and house martins), as well as for the European bee-eater and the common swift.

During monitoring, we record the species and number of birds sighted, time of passage and when possible, for the birds of prey, the age and sex of the individual migrating birds.

Most of the sightings took place during the first half of May, the period when the migration of different species occurs most often.

There are seven days in May that rank among the top ten days for the most sightings, 7th May 2014 being the leader, with 10,024 birds.

The temporal accuracy of the studies made it possible to construct a bird passage schedule, which also accounts for 7th May 2014.

We can observe how the European honey buzzard passages are concentrated between 12:00 and 18:00 (with a peak of 305 sightings at 15:55 on the Sicilian side), then suddenly stop.

On that day, the other species maintained very different schedules: the European bee-eater was sighted throughout the day, while the house martins and swifts preferred the morning. Others, like the Western marsh harrier were only seen in the afternoon.

Considering the second most sighted species, the swallow, the data shows 30 August 2015 as the day with the most sightings, but with one particularity.

Unlike the European honey buzzard, who is observed throughout the day, on 30 August 2015, there was heavy swallow passage in the evening, with two flocks of 2,500 and 4,500 swallows six minutes distance from the Serro monitoring station.

The data confirms not only the absence of collisions of birds of prey with conductors, but also a source of new information for studying migration.