Usually nests of Sandwich Terns are counted by observers who walk through the colony and take inventory of the number of nests and eggs. This is a very disruptive method: during the time that the observers take inventory of the nests, the terns fly up, and are thus unable to keep their eggs warm. In addition, the observers must be very careful to not accidentally step on a nest and destroy the eggs.
In the search for a less disruptive way we ended up with drones. The disturbance effects of a drone were found to be minimal, making it an ideal tool for monitoring and counting nests.
We count the Sandwich Tern colony on Griend twice every year with a drone. Once during breeding, and just before the chicks are able to fly, which gives us the chance of determining the breeding success.
The drone count on Griend is done by flying the drone in an S patern over the colonies at a fixed height while continuously taking images. These images where put together into a orthomosaic, and analysed by our image analysis software, which gave us an exact count of the amount of Sandwich Terns and the amount of nests.