I think that perhaps we are looking at signs of darkness, not only by reason of the 'feather' markings around the perimeter of the glyphs but also because of mauga.

Could it be so that the glyph type mauga is a picture of a black cloth hiding something behind? This something might then be a uniting symbol for the Sun + the Moon, designed as an oval shape with a rhomb inside below.

Though mostly the oval shape is more like an elongated ellips, more like an idea for the planetary orbit of Mars.

I remember having read somewhere (Heyerdahl 3?) that the inhabitants on Easter Island used to hide their heads under a black cloth when they were about to go to sleep. Maybe they took after a noisy bird in a cage, who easily could be put to sleep by throwing a black cloth over.