Prevention of Mortality and Power Outages on 22 kV Lines Related to Mute Swan Collisions by Using Bird Flight Diverters in Slovakia

In November 2021, power outages were recorded on the 22 kV line due to swans. Particularly during evening flights, in direction from the feeding site with an oilseed rape to the roosting site on Danube River, there were repeated collisions, often accompanied by power outages.

Therefore, it was decided by the relevant grid operator to mark the risky sections with dynamic markers – the FireFly bird diverter. The installation was done from the ground, using a hot-stick.

The field survey (12/2021-03/2022) was conducted by one trained field assistant from Raptor

Protection of Slovakia and composed by carcasses survey and flight observation monitoring of bird reactions on marked power line (1.2 km in total length). In the morning, starting 0.5 hour before dawn, and continuing for another 1.5 hours after sunrise. In the evening started 1.5 hours before dusk and continuing for 0.5 hour after sunset. The carcass survey consisted of a walk under power line. Flight monitoring was conducted primarily at dusk (23 vs 2 visits in dawn), as all incidents occurred while the birds were returning from the fields to the water.

1 In total 41 victims of swans were identified under the surveyed power line, 12 before the marking and 29 victims after the measures were adopted. The higher number of posttreatment victims was due to stronger tailwinds and does not demonstrate the effectiveness of the diverters. Within the monitoring period, 6 collisions were directly observed, accompanied with flashes due to short circuit, a result of very strong and turbulent north-western tail wind that pushed the swans to the ground while crossing the marked power line. These windy conditions account for 25 carcasses out of 29 in total. All collisions happened only during the evening return to the roosting water area, confirmed by the position of the bodies.

In 25 site visits (on December 10, 18, 19, 22, and 23; January 3, 5, 6, 11, 14, 17, 18, 30, and 31; February 4, 13, 15, 16, 17, 23, and 24; March 7, 15, 22, and 23), totally 6,086 overflights of mute swan individuals were recorded (62 hours of live observations). Over the 3 months since treatment, based on flock size (280 individuals on average) and a minimum of 2 overflights in one day, there were at least 82-90 flock flyovers accounting to 23-25,000 individuals. Installed bird flight diverters proved to be an effective option to reduce bird mortality on power lines. Another goal of the monitoring was to highlight the importance of being physically present and observing the birds' behavior and influence of external factors.