...when a koro festival was given in honour of one's father "an expert was called in to commemorate the old man's deeds, 'how many men he had killed, how many chickens he had stolen', and a tablet was made accordingly". In all likelihood, the tablet that was made for this was called the kouhau koro.

But in addition to this tablet commemorating a father's deeds there was also 'a larger tablet containing a list of these lesser ones, and giving merely the name of each hero and the year of his koro'. It was probably this larger tablet that was the actual kouhau ta'u (lit. 'year staff, tablet of years')...

...The ta'u category of rongorongo inscriptions - that is, the alleged kouhau koro and kouhau ta'u - is perhaps the closest thing in the Easter Island classical script that approximate what Western scholarship would designate to be island historiography. The word ta'u means 'year' in Old Rapanui (Modern Rapanui uses Tahitian matahiti), so that one can reliably assume that the category does indeed in some way register historical events or names.

I would discount any possibility of a confusion with a hypothetical Rapanui chant called tau (without the glottal stop) based on many West and East Polynesian analogies; there is no documented Rapanui tau chant and the glottal stop in Rapanui ta'u is clearly attested.

(Fischer)