Additionally, it's an "r-colored" vowel, and it's schwa like (See note 2. in the same source above). And from Symbols for American English Vowel Sounds,
"R-colored" or rhoticized vowels (such as those in beard, heard, hard are hard to discriminate and are absent in "r-drop" or non-rhotic dialects such as those typical of the North American South and New England region, and Received Pronunciation in GB. In these latter dialects, the preceding vowel is usually lengthened and often glides toward the central schwa sound. IPA hangs a little "r-hook"diacritic off of the symbol for an r-colored vowel.