sicklebill
well-known Cretaceous relic
I think it's like with many Arabic names, with non-standardised versions of spelling, don't really care either way, we went through all this with Macgregor/MacGregor's Bowerbird and either seemed fine to me. I don't have a problem with Spot-breasted Cuckoo Dove.I suspect it's only recently that people make a firm distinction between Mac and Mc. Before people had a need to use their surname regularly it was probably interchangeable. All variants derive from the Gaellic Mac. Directories traditionally put Mc/Mac before Ma in alphabetical listings so the c/ac is effectively treated as a separate letter, which can be written either way.
I learnt that Mac was Scottish and Mc Irish, but this distinction doesn't turn out to be true. Nor does the association of Mc with Catholics. Mc might be more common in Ireland, though, which lends some weak support to McKinlay.