How to pronounce The BIRD R-Vowel /ɜr/ in American English

Flare your lips and push them slightly outward, almost like you're starting to whistle. Inside your mouth, lift the body of the tongue toward the center of the hard palate, and press the sides of your tongue firmly against the insides of your upper back teeth. The tip hangs down but pulls back slightly so it doesn't touch the teeth. Because the flared lips hide the tongue, you have to focus on the physical feeling of that lift and side-bracing rather than what you can see in a mirror.

American English heavily pronounces the R; British Received Pronunciation drops it entirely. In a British accent, bird and turn use a long central vowel with no R-coloring. To sound naturally American, the R has to dominate the entire syllable, with no separation between a starting vowel and an ending R. The lips flare and the tongue lifts, and one continuous heavy R carries the syllable from start to finish.

English spelling is messy, but in stressed syllables, IR, ER, UR, and OR (after W, like in word) usually make the /ɜr/ sound when they sit at the end of a word or before another consonant. Bird, her, turn, earth, nurse, word: your mouth makes the identical flared-lip, lifted-tongue shape every time. Don't let the different written vowels trick you into changing position. The heavy R-coloring takes over completely, neutralizing whatever vowel the spelling suggests. (Note: when the same letters sit before a vowel in the next syllable, like very, spirit, or syrup, this rule no longer applies.)