Tavake can refer to the tropic b

Tavake in Nga Tavake a Te Rona could refer to the name of one of the tropic birds:

"Tavake is the general Polynesian name for the tropic bird, whose red tail feathers were very popular. This name is closely connected with the original population." (Barthel 2)

"The Red-tailed Tropicbird, Phaethon rubricauda, is a seabird that nests across the Indian and Pacific Oceans. It is the rarest of the tropicbirds, yet is still a widespread bird that is not considered threatened. It nests in colonies on oceanic islands. The Red-tailed Tropicbird looks like a stout tern, and hence closely resembles the other two tropicbird species. It has generally white plumage, often with a pink tinge, a black crescent around the eye and a thin red tail feather. It has a bright red bill and black feet ...

When breeding they mainly choose coral atolls with low shrubs, nesting underneath them (or occasionally in limestone cavities). They feed offshore away from land, singly rather than in flocks. They are plunge-divers that feed on fish, mostly flying fish, and squid." (Wikipedia)

Nga marks plural:

Preposed plural marker of rare usage. 1. Sometimes used with a few nouns denoting human beings, more often omitted. Te ga vî'e, te ga poki, the women and the children. Ga rauhiva twins. 2. Used with some proper names. Ga Vaka, Alpha and Beta Centauri (lit. Canoes). Vanaga.

It seems impossible to connect plural with Spring Sun, he has only one 'leg' and spring is singleminded. Nga Tavake must belong beyond midsummer. And this seems to agree with where Ira found him:

"Through the meeting with Nga Tavake, the representative of the original population in the area north of Rano Kau, the number of the explorers is once again complete. Not only are Kuukuu and Nga Tavake related as 'loss' and 'gain', but also they share the same economic function: it was Kuukuu's special mission to establish a yam plantation after the landing (in his role he represents the vital function of the good planter); Nga Tavake joined the explorers to work with them in the yam plantation of the dead Kuukuu (i.e., he closes the gap caused by the death of Kuukuu among the planters.)" (Barthel 2)

Nga Tavake A Te Rona was found at the back side of the island, the side of the Moon. The important feature of the bird was its thin red tail feather. Red at the end suggest a fire at the end of a cycle.