'Birder' definitions:

Definition of 'birder'

From: WordNet
noun
A person who identifies and studies birds in their natural habitats [syn: bird watcher, birder]

Definition of 'Birder'

From: GCIDE
  • Birder \Bird"er\ (-[~e]r), n.
  • 1. A birdcatcher. [1913 Webster]
  • 2. a birdwatcher. [PJC]