Thanks Jimbobh! I really appreciate your help!
It wasn't easy but I figured it out and the honor belongs to you Jimbobh . The only thing different was the scripts in your video. The flock bundle comes with the .cs-files in scripts folder. So they are C# scripts and you were using java scripts (.js-files). There is a JS script package in the C# Scripts folder of the bundle and there are the needed java scripts but it still wasn't easy.
So do just as I say Clubcaptain and you will get this to work. Just to warn you beforehand, birds will have a quite major impact to fps if you over react like me .
Here we go.
1. Delete the whole Bird Flock and all the files that came with it from Assets folder or from it's sub folders (IMPORTANT: scripts must be destroyd too!!!!). This doesn't destroy your flock boxes in scene, they just dissapear for a while from the screen.
2. Go to asset store from Unity and select the download symbol from the top of the window. You can see all your downloads from Unity asset store. Select Bird Flock Bundle and press import. Then you will have a window where you can check and uncheck assets. UNCHECK all the C-sripts in the cripts folder and then press Import.
3. Now you have the Bird Flock again in your assets folder but no scripts. Now go to the C# Scripts folder and double click the JS script package and import those java scripts. They will go to the Scripts folder of your bird flock. Now your bird flock boxes should appear again to the scene.
4. Drag those .js script to the Standard asset => Scripts folder.
You are done.
If you try to do this in different way you'll probably fail. I tried many ways and this was the only way I got those .js-script files to work. If C-scripts are imported, Unity will not accept anything else.
Don't panic . May the force be with you!
I'm going to FORCE myself to try one more time :-)