Science - October 27, 2015

Birds are not disturbed by drones

Roelof Kleis

In principle, drones are a nice means to keep an eye on the nature of the Wadden. But does this not disturb the birds? It is not too bad, so it appeared from the firsts tests.

The test was performed by marine ecologist Martin Baptist of Imares. Baptist flew a drone at one hundred metres above a dried piece of mudflat in front of the coast near the neighbourhood Koehoal North of Harlingen. The bird movement before, during and after the drone flight was observed from the dike. The result: the drone had no or barely observable effect on the behaviour  of the birds on the mudflats.

‘At least not at this time and place’, Baptist holds to the scientific ways. Wat a drone’s effect is near a large group of birds is not clear. ‘At 800- 1200 meters of the dike, a dense group of shorebirds are foraging. Our drone flights
went until 500 meters from the dike, so we did not fly over them.’


That the test was performed at Koehoal has a reason. At this place next year the project mud motor will start. The mud motor will gather silt from the neighbouring Harlingen to use to grow the salt marshes near Koehoal. Baptist is the project leader of this building with nature. ‘A million cubic meters of clean silt is dredged from this port on a yearly basis. This is spread just outside the port of the Waddenzee. But this silt is excellent building material to grow the salt marshes.’

Thus the mud motor is a variant on the sand motor which was used to create a peninsula in front of the Zuidhollandse coastline, used as a coastal defence. The plan is to spread the silt near the salt march, and let nature do the rest of the work. The natural accretion of the marsh is expected to double from the current 1-2 centimetre per year to 2-4 centimetre.

Drones will have to follow this growth with accurate photogrammetry. Baptist: ‘With photogrammetry you fly several times over the object that you are photographing. This yields photos of the object from different angles. With a few calculations you can determine the height of the object.’ With the drone at Koehoal such a detailed terrain model was made. The mud motor will start in September next year.

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