Complex sentence: Tafforet was familiar with the fauna of Réunion, where the hoopoe starling lived, and otherwise made comparisons between the faunas, so the fact that he did not mention a crest on the Rodrigues species indicates it was absent.
Split into simpler sentences: Tafforet was familiar with the fauna of Réunion, where the hoopoe starling lived. He usually made comparisons between faunas, so the fact that he did not mention a crest on the Rodrigues species indicates that it was absent.