A bird or creature that chirps; a person who speaks in a cheerful, lively manner; something that makes chirping sounds.
From 'chirp' + '-er' (agent suffix). The suffix '-er' transforms the verb 'chirp' into a noun meaning 'one who chirps,' a productive pattern in English for creating agent nouns.
The '-er' suffix is one of English's most powerful word-building tools—you can add it to almost any verb to create a noun for 'one who does that thing,' which is why English has hundreds of agent nouns and why non-native speakers can often guess what a word means even if they've never heard it.
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