Technical preview, not a production service. The model is validated (see below), but none of these cities has a radar close enough to check the forecast the next morning. Treat it as an indication, not a settled figure.
The latest night on the radars
Night of 16 October 2026, as 37 radars in Spain, Portugal and France saw it, every 20 minutes.
5.9 birds/km² on averageS · 5.9 m/s overall headingToulon busiest radar
Colour is the density of birds in flight; arrows show where and how fast they were heading over each radar. Where no radar sees, the map fades out. It is the latest complete night: the open radar profiles are published about two days late. With data within hours this map would be ready every morning (proposal ).
The nights ahead Updated on 19 October 2026. 7 nights, 29 cities.
The level is relative to each city , not an absolute number of birds: “very high” means the night falls in the most intense 10 % of the record for that same city . That way the alert means the same thing in Seville and in Bilbao, even though far more birds pass over Seville.
At the peak of the passage it is normal for several cities to come out high at once: the percentile is measured against the nights of those same dates in earlier years.
city Mon Tue Wed Thu Fri Sat Sun Alicante Spain low low high high moderate very high high Barcelona Spain moderate low high low low moderate very high Bilbao Spain very high moderate moderate low low very high low Bordeaux France high low low moderate low very high very high Cáceres Spain moderate low high moderate very high very high very high Granada Spain high very high high low moderate high moderate Córdoba Spain low moderate high low moderate very high high Faro Portugal low moderate high moderate high high very high Gijón Spain high very high low high low very high low Málaga Spain moderate low very high high very high very high low Nice France moderate low very high high moderate moderate very high Montpellier France very high high very high low high moderate high Madrid Spain moderate low low low high high very high Valencia Spain moderate low moderate low high very high very high Toulouse France very high low low low low very high high Sevilla Spain low low very high low very high very high moderate Santander Spain very high very high low low low very high low Lyon France low moderate low low moderate high moderate Lisboa Portugal moderate low high low low moderate high Coimbra Portugal moderate moderate moderate low low moderate high Almería Spain low high high low high high low Valladolid Spain high low moderate low low moderate moderate Palma Spain low moderate moderate low moderate moderate high Marseille France low low moderate high moderate moderate moderate Murcia Spain low moderate high high high high high Porto Portugal moderate low low low low low moderate Salamanca Spain moderate low moderate low moderate moderate moderate Vigo Spain moderate low low low low low low Zaragoza Spain moderate moderate low low moderate moderate low
Nights to switch off
Mon 19 Oct : very high in Bilbao, Montpellier, Santander, Toulouse; high in 4 more cities.Tue 20 Oct : very high in Gijón, Granada, Santander; high in 2 more cities.Wed 21 Oct : very high in Montpellier, Málaga, Nice, Sevilla; high in 9 more cities.Thu 22 Oct : high in 6 more cities.Fri 23 Oct : very high in Cáceres, Málaga, Sevilla; high in 6 more cities.Sat 24 Oct : very high in Alicante, Bilbao, Bordeaux, Cáceres, Córdoba, Gijón, Málaga, Santander, Sevilla, Toulouse, Valencia; high in 6 more cities.Sun 25 Oct : very high in Barcelona, Bordeaux, Cáceres, Faro, Madrid, Nice, Valencia; high in 8 more cities.
Where they fly. The routes map draws the direction the radars have measured since 2016, night by night, and lays the wind farms of the coming nights on top: which ones are in the way and why the advice is to stop or to keep running.See the routes map → Wind farms Updated on 19 October 2026. 151 wind zones in Spain and Portugal, 24,529 turbines.
The same heavy-passage nights, seen from a wind farm. In the Netherlands the offshore farms are already stopped on nights of intense migration with a forecast like this one; in Spain and Portugal nothing like it is in place. For each zone of about 25 km two things are crossed: how much passage is expected (the same model as the cities, calibrated on five years of ERA5 weather at the zone's point) and what stopping costs (the output the turbines would have that night with the wind forecast at 100 m).
Stopping is only suggested when the passage is very high and stopping is cheap , that is, on nights with little wind. Tested on 2021-2026, that rule would have stopped 7.5 nights per season and zone, for 3 % of the night output, and covered 9 % of the predicted migration; stopping on every very high night would have cost 13 %. And it picks the right nights: the nearest radar measured heavy passage on 67 % of them, against 24 % by chance.
night zones at very high stop stop at peak hours where (largest capacity) Mon 19 Oct 2 2 zones · 236 MW — Priorato, Somontano de Barbastro Tue 20 Oct 20 20 zones · 3,317 MW — Campo de Belchite, Hoya de Huesca, Zaragoza, Albacete
It is a suggestion to rank nights, not a stop order nor a substitute for each farm's monitoring plan. The model does not tell species apart nor know at what height the birds cross each farm, and the nearest radar is tens of kilometres from the farm.
Map, per-zone table and full method: wind farm report ; what the rule would have done since 2021 and how it compares with the radar: verification .
Did we get it right?
Every forecast is published before the night and checked afterwards against what the nearest radar measured. 39 nights verified, from 3 September 2026 to 11 October 2026.
42% of the alerts landed on a busy night34% what chance would get44% of the busy nights had an alert
Pick a night Sun 11 Oct Sat 10 Oct Fri 9 Oct Thu 8 Oct Wed 7 Oct Tue 6 Oct Mon 5 Oct Sun 4 Oct Sat 3 Oct Fri 2 Oct Thu 1 Oct Wed 30 Sep Tue 29 Sep Mon 28 Sep Sun 27 Sep Sat 26 Sep Fri 25 Sep Thu 24 Sep Wed 23 Sep Tue 22 Sep Mon 21 Sep Sun 20 Sep Sat 19 Sep Fri 18 Sep Thu 17 Sep Wed 16 Sep Tue 15 Sep Mon 14 Sep Sun 13 Sep Sat 12 Sep Fri 11 Sep Thu 10 Sep Wed 9 Sep Tue 8 Sep Mon 7 Sep Sun 6 Sep Sat 5 Sep Fri 4 Sep Thu 3 Sep city radar published alert birds/km² measured result Marseille frcol · 82 km high 42.6 ✓ flagged Faro ptfar · 32 km moderate 24.5 ✗ missed Lisboa ptlis · 75 km moderate 16.4 ✗ missed Barcelona esgld · 24 km moderate 14.0 no record Montpellier frnim · 55 km very high 9.4 ✗ false alarm Madrid estjv · 27 km high 8.7 no record Zaragoza espdg · 30 km very high 8.6 no record Almería esnjr · 34 km low 5.6 no record Cáceres essft · 9 km moderate 2.6 no record Sevilla esclg · 45 km high 2.5 no record Bordeaux frbor · 9 km moderate 2.0 ✓ quiet Toulouse frtou · 6 km high 0.9 ✗ false alarm Lyon frniz · 45 km high 0.4 ✗ false alarm
A night is busy if it falls in the top quarter of its radar's own record, and there is an alert when «high» or «very high» was published. The Spanish radars renewed in 2025 do not have a long enough record yet to say what a busy night is, so they show as «no record» and do not count in the percentages. The radar is not in the city: it is the nearest one, tens of kilometres away.
Every figure, week by week and by days ahead: verification report and the data as CSV .
What to do on an alert night What actually reduces collisions and disorientation, ordered by effect and by ease.
Switch off decorative lighting Façades, monuments, skybeams and non-essential signs, from sunset to dawn.
Switch off empty floors and offices Lit upper floors of glass buildings are the ones that attract most birds and kill most of them.
Draw blinds and curtains If the indoor lights have to stay on, keep the light from spilling out of the window.
Aim the light at the ground Luminaires with all their output below the horizontal and a warm colour temperature (≤ 2,700 K); blue light is more disorienting.
Where birds and light overlap most Exposure ranking for autumn: the artificial brightness of each city's sky multiplied by the bird density forecast on its ten most intense nights, normalised to 100 at the most exposed city in the set. It follows the method of Horton et al. (2019).
city sky vs natural birds/km² on peak nights exposure 1. Madrid Spain 44× 9 100 2. Barcelona Spain 36× 10 86 3. Lisboa Portugal 38× 8 77 4. Marseille France 17× 14 59 5. Valencia Spain 35× 5 45 6. Porto Portugal 29× 5 38 7. Zaragoza Spain 18× 8 36 8. Montpellier France 15× 9 35 9. Lyon France 21× 6 31 10. Nice France 12× 9 27 11. Sevilla Spain 28× 4 26 12. Coimbra Portugal 7× 14 25
The “sky vs natural” column says how many times brighter that city's sky is than a sky with no artificial light. A caveat: between the most and the least lit city there is a factor of 3-4, while in birds there is barely a factor of 2, so the ordering is driven mostly by light.
How it is computed From a radar echo to a lights-out alert, in nine steps and without acronyms.
A weather radar sees birds too A weather radar is an antenna that turns and sends out microwave pulses. When a pulse hits something — raindrops, a bird, an insect — part of it comes back. The radar measures how much energy returns, which says how much “material” there is, and how long it took, which says how far away it is. To look at different heights it repeats the turn with the beam tilted more and more, from half a degree to over ten. Every 5-15 minutes it has a full volume of the air around it.
It also measures the Doppler effect : the small change in frequency of the echo when what reflects it moves towards or away from the antenna, like an ambulance siren changing pitch as it passes. That is where the birds' speed will come from.
The air, cut into 200-metre slices An open program, vol2bird (Dokter et al. 2011), takes each volume, keeps the ring between 5 and 35 km from the radar and cuts it into horizontal slices 200 m thick. For each slice it computes:
Density : the total echo divided by the echo of a typical bird, a small songbird with 11 cm² of “radar surface”. It comes out in birds per cubic kilometre.Speed and direction : if the birds head north-east, on that side of the radar they move away and on the opposite side they come closer. Fitting that pattern all the way round gives where the whole lot is going and how fast.Disorder : how far the measured speeds stray from that common movement. Rain and insects drift with the wind and give a clean pattern; birds each fly their own heading and give a messier one. A slice with less than 2 m/s of disorder counts as zero birds.From the weather service to this page The Spanish radars belong to AEMET, the Portuguese ones to IPMA and the French ones to Météo-France. Each service sends its volumes to OPERA , the network that pools the weather radars of almost all of Europe. Aloft , a European scientific archive, runs vol2bird on those volumes and publishes the profiles openly (CC0), one or two days late and without quality control. Sub Nocte downloads them from there: one file per radar and day, with one row per slice and per profile.
One night, one figure The slices between 200 and 3,000 m are added up, each one as its density times 0.2 km of thickness. The result is how many birds there are in the air column over one square kilometre of ground. Then all the profiles of the night are averaged, from when the sun drops 6° below the horizon until it climbs back past it. That is the page's central figure: the nightly VID , in birds/km².
VID = Σ density × 0.2 km → mean over the night
BirdCast uses another unit: how many birds cross an imaginary 1 km line during the night (MTR). It is density times speed, so it needs the speed. Here it is computed only when at least half of the night's density has a measured speed; otherwise it is left empty, never set to zero.
What a heavy night is, place by place From each radar's record since 2016 we work out, for every day of the year, what a normal night looks like and where the 70th and 90th percentiles fall. Sanity check: the most intense 10 % of nights carry 50-55 % of the season's passage in Spain, Portugal and France, the same share measured in the United States (54 %).
Weather explains a good part of that figure Using eleven years of nights from 55 radars in Spain, Portugal and France we train two models: one estimates how many birds there will be and the other decides whether the night will carry heavy passage. The variables are the wind at the heights where they fly (750, 1,500 and 3,000 metres), split into the part pushing along the migratory heading and the part pushing sideways; temperature and its 24-hour change; humidity, cloud cover, rain and pressure; and the day of the year.
Validation leaves whole radars out Not random nights. It is the only honest test for a city without a radar: the model is trained without that radar and then asked to predict it blind. Done that way it captures 34 % of the heavy-passage nights against the 10 % that chance would give, with 66 % false alarms. Three times better than a coin flip, and wrong fairly often.
The alert is calibrated city by city and date by date The model is run over the weather from 2021 to today at the city's exact location, and the levels are cut at the percentiles of the nights around the same date, in a window of three weeks either side: moderate above the median, high above the 75th percentile, very high above the 90th. That is why the alert needs no radar in the city, means the same thing everywhere and still means something at the peak of the passage.
Every forecast is checked afterwards Each day's forecast stays in the repository history with its date. Every Monday the past ones are retrieved, what the radars measured afterwards is downloaded, and the result is published in the verification report.
Two gaps in the data Going through the files slice by slice turns up two shortcomings that are not in the archive's documentation. They are measured, not assumed, and they explain a good part of why the Spanish cities are the hard case.
In Spain the radar only looks at the first kilometre On AEMET's renewed radars there is echo only up to about 900-1,000 m above the antenna: five or six slices. Above that the file carries not a single measurement, of birds or of anything else. With the same program, Porto reaches 3.7 km above the antenna and Nantes 4.7 km.
0.5° 1.5° 3° 5° 7° 0 5 15 25 35 45 1 km 2 km 3 km 4 km what arrives from Spain what arrives from Porto or Nantes distance from the radar (km) What the radar sees, with height exaggerated. The lines are beams at different tilts; the light band is the 5-35 km ring vol2bird uses. The most likely explanation is geometric. At 35 km from the radar, a beam tilted 1.5° passes a little over 900 m above the antenna, plus about 100 m more because of the Earth's curvature. Only the steeper beams see the higher layers. If only the lowest turns reach the European network, the ceiling lands right there. It is a hypothesis still to be confirmed with AEMET.
Consequence: birds flying higher are not counted. That is why a Spanish radar's figure is never compared with another country's here: the levels are each radar's own percentiles.
Speed is often missing, and in France almost always Speed comes from the Doppler. This is the share of slices with birds that carry it:
In France the archive had it complete in 2019 and loses it from 2021 on. The program that computes it is the same, so the most likely cause is a change in how the Doppler data reaches the European network. On the renewed Spanish radars it is there in a bit under half of the slices with birds in spring, and almost never in winter, when there are hardly any birds. AEMET's old radars always gave it.
Consequence: without speed there is no traffic rate (MTR) and no disorder filter to set insects apart. That is why the central figure is the VID, which needs only density. Still to ask Aloft whether the Doppler data is in the source files and whether 2021-2026 can be reprocessed.
Measured on the Aloft profiles in October 2026.