The reason I ask is that you told us that Otto was a male but I noticed that his cere looked much more like a female in the last year of his life. Testicular tumors are pretty common in male budgies and they secrete hormones that can turn a male budgie's cere tan brown and wrinkled like a females. My female Lutino Elan has a cere that looks like Otto's before be passed.
This may have been why he died. If so, you couldn't have done anything about it.
This is my girl, Elan.
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