A prolific egg collector from Nottingham has been convicted of having equipment used to target birds' nests.
Aaron Kisiel, 39, from Hanley Avenue, Bramcote, had denied three charges of possessing items capable of being used to take and possess wild birds' eggs.
Magistrates heard RSPB officers seized a book on bird behaviour and climbing equipment from his home in May 2009.
Kisiel, who had admitted possessing 28 wild birds' eggs, was warned he faces jail when he is sentenced next month.
The RSPB said Kisiel's actions were "completely wrong" and said they feared they had uncovered only a fraction of what he had done.
They found diaries which indicated he had been active for about 16 years, along with egg display cabinets and syringes for emptying out the shells.
RSPB officer Mark Thomas said: "It is very strange behaviour. He was completely obsessed, he didn't have a job.
"He is perhaps the most destructive person, in terms of birds, in the East Midlands."