I presume the decoy site was shut down before 1945 when it became a nature reserve.
Most decoy sites closed by 1944, the official disposal instructions were sent in October 1944 but closure will have happened long before that for most sites, especially on the Western side of the country.
I'll keep my eye for specific Hibre dates, I most probably have the information but it is somewhat disorganised.
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We don't do charity in Germany, We pay taxes. Charity is a failure of governments' responsibilities - Henning Wehn