John C Wells writes: "But what David Attenborough said on TV last night, repeatedly, was ˈliːmʊə. I don’t think I have ever heard that before." The other blogger, Jack Windsor Lewis, opines: "This [= JCW's observation] very much surprised me becoz [sic] I too watched that program and, tho [sic] I he·rd [sic] him say that word more than twenty times, on no occasion did it strike me as ending with /ʊə/."
Who is one to believe? Well, the best thing is to listen for oneself! So one listened to episode one.
I spotted 22 instances of the word lemur/lemurs in this episode of nearly 59 minutes of length. Sir David's pronunciation vacillated between an unstressed mono- and diphthongal second syllable. If it was a monophthong (N = 17) it was mostly a schwa or /ɔ, ʌ/, otherwise (N = 5) I heard /ʊə/ or /ɔə/.
Addendum: I also watched the second and third episodes of the documentary on Madagascar: Again Sir David's pronunciation vacillated between a mono- and a diphthongal second syllable in the word lemur.