To prevent collision fatalities, wind turbines can be shut down in response to the level of bird flux. Flux levels are assumed to be linearly related to collisions. The percentage of fatalities that could be prevented, if turbines were to be shut down at those flux levels, is therefore the same as the percentage of migration during those hours compared to the total seasonal migration. Krijgsveld et al. (2015) constructed a table containing this information for vertical radar.
We present similar tables summarising nocturnal bird flux for two offshore wind farms; Luchterduinen (LUD) and Borssele Aplha (BSA), for two different radar systems; horizontal radar (HR) and vertical radar(VR), for the different migration seasons (spring and autumn) and for different lengths of the season( full season of 3.5 months) and short season; only using the months as used for training the migration prediction model by the Bradaric et al. (2022) ). Tables were constructed based on hours of a specific year and for all years together.
Flux class: the range of flux as measured by the radar, also known as mean traffic rate(n birds/km/h). A square bracket indicates that the value itself is included, a round bracket indicates that all values until that value are included.
Sum n hour: the number of hours that a certain flux class occurred for that season.
% time: the percentage of the total number of hours that a certain flux class occurred.
Cum. n hour: the cumulative number of hours with radar data that a certain flux class and higher occurred.
Cum. n hour (%): the percentage of the total number of hours with radar data that a certain flux class or higher occurred. This column also represents the cumulative percentage of idle time, if turbines were shut down during hours of this flux level or higher. E.g. in the first table the value 0.21% for flux class [400, 450) indicates that in 0.21% of the total time, which is 2 hours of the total 957 hours, fluxes larger than or equal to 400 birds per km per hour were reached.
Sum MTR: the total summed flux for a certain flux class measured during the season for that year in birds/km.
Cum. MTR: per flux class the summed flux for all hours that a certain flux class and higher occurred. E.g. in the first table the value 1988 (n birds/km) for flux class [350, 400) indicates that 1988 birds flew by when fluxes values larger than or equal to 350 birds per hour per km for this season and year.
Cum. MTR (%): the percentage of cumulative flux compared to the total flux measured for all available hours for that specific season and location. Since flux is assumed to be linearly related to collisions, this column also represents the cumulative percentage of collisions avoided, if turbines were shut down during hours of this flux level or higher.
Mean wind speed (m/s): the mean wind speed during hours of a certain flux class.
Sum power (kWh/MW): the potential power generated per mega Watt of a wind turbine is calculated per hour. This column represents the summed power per flux class.
Cum. power (%): the percentage of cumulative power compared to the total power for that season and year. E.g. in the first table the value of 0.33% for flux class [350, 400) indicates that for the total 5 hours (3+1+1) where MTR was higher than or equal to 350 birds/km/h in total 1582 kWh/MW (=217.06 + 337.09 +1028.58) was generated for the total power generated for the available hours for this season and year (=473837 kWh/MW).
Row nr: this column is added to be able to sort all columns back to the original order.
Additional columns for All year-tables.
Seasonal migration can be quite different in the total amount of migration, in the peakedness of migration(sometimes uniform, sometimes large peaks), and also in the detection of migration (some years with good weather circumstances where radar functions very good, and some years where many hours have to be exclude from the analysis). Due to these differences, some years might be over represented in all years table. Therefore columns with the median, minimum and maximum of the different years were added to show differences between years.
N unique years: the number of years where this flux level was achieved
Median (min – max) cum. n hour: the median, minimum and maximum cumulative percentage of total hours measured over the available years.
Median (min – max) cum. MTR (%): the median, minimum and maximum cumulative percentage of total flux (birds/km/h) measured over the available years.