Every winter dawn at a marsh in northern Jutland, thousands of pink footed geese lift off the water at once.
A gray brown cloud rises over the reeds.
They fly out to feed in nearby fields, then come home at dusk.
Between the roost and the fields stands a row of tall white turbines.
The environmental permit for the site set a hard ceiling on how many birds could be struck there.
So what actually happened when the flocks met the blades?
Flocks bend their flight path around the whole turbine row
The mechanism turns out to be simple. Geese and cranes do not wait until the last second to dodge a spinning blade, they reroute long before they reach the turbines at all. Radar at a wind farm in northern Jutland tracked birds moving between their roost in a protected marsh reserve and the feeding fields beyond the turbine rows.
Instead of threading between rotors, the flocks bent their whole flight line around the cluster of machines. Pink footed geese avoided collisions mainly by avoiding the entire wind farm, while common cranes did not actively avoid entering it and proved good at maneuvering between the turbines.
That distinction matters. A bird dodging at the blade is a near miss. A bird rerouting well before the first rotor has already filed the turbines away as an obstacle, the way traffic bends around a roundabout long before the first car reaches it.
Twenty two turbines tower over one of Denmark’s most important bird roosts
The scene itself is striking. The repowered wind farm includes 22 turbines with a hub height of about 305 feet, a rotor diameter of 371 feet and a tip height of roughly 490 feet. That is a rotor wider than a football field is long, set beside a protected wetland where tens of thousands of geese spend the winter.
Jesper Kyed Larsen, bioscience lead at the utility Vattenfall, described the setting as “quite extraordinary, as 20-30,000 pink-footed geese and several hundred cranes roost here.”
Because the stakes were high, regulators wrote a hard ceiling into the project’s environmental approval. Conditions in the permit stipulate that collisions must not exceed 75 percent of the current sustainable mortality rates for the pink footed goose and crane populations. That is a limit pegged to what the populations can absorb, not permission to lose a fixed share of the flock.
Crews searched beneath eleven turbines every three days
The count came from fieldwork, not modeling. For three stretches of just over a month, in both the first and the third year after the farm went up, the ground around 11 selected turbines was checked every three days across autumn, winter and spring. The totals were then adjusted for what foxes and similar animals remove before a search crew arrives.
Every search started from a conservative assumption rather than a generous one. The study assumed that all birds or remains of birds found under the turbines could have been involved in a collision, stacking the odds against the machines rather than for them.
Even with that bias built in, the tally barely moved. For both geese and cranes, the calculated evasive response over the two study years stood at 99.9 percent, based on a population of 20,000 to 30,000 geese and several hundred cranes. The analysis was published in 2021 in the journal of the Danish Ornithological Society.
Thousands of daily flights, and no strike anyone could confirm
What the ground crews never found was as telling as what the radar showed. No carcasses or remains of common crane were recovered at all, and neither geese nor cranes were found where it could be stated with certainty that they had collided with the turbines. The published analysis concluded that no cranes and only a few pink footed geese were struck annually at the site.
The daily traffic through that airspace is heavy. Each day thousands of birds leave their roosting areas in Vejlerne and fly out to nearby fields to find food, with many passing the wind farm. That volume is what makes so small a tally worth noticing.
A comparable pattern has shown up around offshore installations, where two years of camera and radar monitoring in the North Sea recorded not a single bird colliding with a rotor blade. Larsen has cautioned that the offshore work was promising but not actually designed to detect collisions.
One lower bound, researchers say, not a universal rule
None of this means turbines are harmless everywhere. The finding reads as a floor rather than a guarantee, and Larsen put it this way: “Hardly any of them hit the turbines, and the figure is considerably lower than previously believed.”
Species, terrain and weather all change how readily a flock reroutes. Smaller songbirds behave differently from geese flying in tight, visible skeins, so the result travels only so far beyond this one marsh.
The same utility is now involved in a trial at a Dutch wind farm testing whether painting one blade of a turbine black reduces bird strikes, a question raised by earlier Norwegian work on the island of Smola that reported far fewer strikes after one blade was darkened, work that sits alongside other structural experiments around turbine foundations elsewhere. The marsh is still full of geese every winter, lifting off at dawn, and the turbines beside them are still turning.
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