I just wanted to let everyone know that the birds have started nesting again. They started bringing in material around the the 19th of March. And 80 grams later the female now seems to be almost permanently inside the birdhouse (please see the image below). For comparison: Last year they also started bringing in material around the 19th of March and the female started nesting on April the 13th. The nest last year also weighed about 80 grams. It amazes me to see how precise the birds are timing all of this (without wearing a watch ;-) ).