Madcap and Rare bird

Madcap noun - A person who seeks out very dangerous or foolhardy adventures with no apparent fear.

Rare bird and madcap are semantically related. In some cases you can use "Rare bird" instead a noun "Madcap".

Rare bird noun - A rare or unique person.

Madcap and rare bird are semantically related. Sometimes you can use "Madcap" instead a noun phrase "Rare bird".