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The Hanover eagles' nest collapsed away to nothing, after serving its purpose. The family would only visit it every once in a while.
It was interesting to see the progress of the nest, and to realize: this collapse happened on purpose.
When they build, the eagles complete the basic structure of the nest with just sticks; then they start bringing straw/dry grass to the middle, and they keep on bringing that until the eggs hatch. That makes the nest comfy, with a safe resting place for the eggs.
When the nest is just sticks and a little straw, rain can easily just seep through. It drips away, and the eggs stay dry. But as the birds are are always bringing straw, it builds up. Eventually, the bottom layer stays damp with rain that has dripped through the top layers. After a while, that layer turns to mulch.
This creates a very solid platform. (It has to hold up to 75 pounds of moving/landing birds.) The original sticks are like the beams, and the straw/mulch is cement and planks between them.
As the youngsters grow, the nest "fills up" and the mulch bottom layer gets thicker. Now all that mulch is rotting the sticks away. Once enough sticks are rotted, the whole thing becomes unstable.
The timing of all this has been worked out over millions of years. The birds start with a stick size that will take 6 months to rot away - just enough time for the youngsters to fledge. They bring just enough straw to make this rot happen with the right timing. So the Hanover babies learned how to live outside the nest, and three weeks later, the nest collapsed. Hand of evolution.
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