It's a patent drawing. Compared to those other "flying bird cages", it's a very clean and elegant
design, I think.
But THAT site actually seems to be a gold mine ! It's a pity, that those pictures are very low res indeed,
but as it is run by an official German foundation, maybe there's a chance to get some help.
The basic website is made with creative artists in mind, but we all ARE artists, aren't we ?