Question

ɜ British and other non-rhotic English dialects in bird, girl, nurse, curl. Rhotic dialects (like most American English) have [ɝ] instead. Similar to the schwa, but always stressed and non-reduced.

Accepted Answer

Open-mid Central Unrounded http://en.wikipedia.org/wiki/Open-mid_central_unrounded_vowel

Symbol	ɜ
Name	Open-mid Central Unrounded
Notes	British and other non-rhotic English dialects in bird, girl, nurse, curl. Rhotic dialects (like most American English) have [ɝ] instead. Similar to the schwa, but always stressed and non-reduced.
Ref	http://en.wikipedia.org/wiki/Open-mid_central_unrounded_vowel

Central Unrounded Dialects I Rl ɜ Open Mid British