On 27th March, the complete grassland was treated with Glyphosate; by that time I did not know it was Glyphosate as the farmer is treating the land with a poisonous substance more often.
On the 7th and 8th of April both owls came together and stayed much longer around the birdhouse. I could read the females owl complete ring number and learned that she was born in 2010 in a small village nearby. Their behaviour was obviously, they were mating and very busy in the birdhouse so I took it for granted that they would moving in soon.
But, on Thursday 9 April the complete farmland was ploughed and changed from a green into a brown field and with this action it lost its function as food resource. In the night from the 9th to the 10th April I heard them for the last time and since then they did not return.