That's a 'slender R' (because of the preceding slender vowel [e + i]), which has a bit of variation in how it is pronounced.
Careful,
letter ≠ vowel when it comes to Gaelic spelling and pronunciation. The written letters indicate all sorts of stuff but don't necessarily correspond to an actual sound. For example in
sir/ʃirʲ/ the
i both has a sound value (/i/) and doubles up as a quasi-diacritic to tell you the single r that follows is /rʲ/ (and not /r/). But in
cuir /kurʲ/ the
i does not correspond to a sound per se, it merely indicates the
r is /rʲ/.
There are, summing up the other page, two principal ways in which native speakers say single slender
r: /rʲ/ and /ð/ and it's this latter one which sounds a bit like /d/. It's the same sound you get in English
the /ðə/. If you struggle with the 'lisped' /rʲ/ then the best solution is to go with /ð/. Sounding a tad Hebridean is better than sounding non-native
