IPA: /ˈbɜːrdər/
KK: /ˈbɜrdər/
A person who observes or watches birds as a hobby or for enjoyment.
My grandfather is an avid birder who spends every weekend in the park looking for different species of birds.
Birder → The word is formed from "bird" (from Old English "brid", meaning a young bird or chick) and "-er" (meaning a person who). A birder is a person who observes or identifies birds.
Think of someone who is a 'person' ('-er') that is interested in 'birds' — that's what a birder is.