Nowadays there is only one single species of starling in central Polynesia, the Rarotonga starling (Aplonis cinereacsens Hartlaub & Finsch), which occurs exclusively on the island of Rarotonga, the largest of the Cook Islands; another form, the Plain Starling (Aplonis mavornata Buller), itself a mystery for over a century, came from another of the Cook Islands, namely Ma’uke.
So, it’s pretty certain that other forms were once found on other islands in this archipelago, right?
I just found a clue in this direction when I was writing down the names from a list of birds compiled in the early 20th century by someone named F. W. Christian; this list is part of a kind of dictionary of the Mangaian dialect, the dialect spoken on the island of Mangaia, the southernmost and second largest of the Cook Islands.
Here a list of the bird names.:
“Pā-Tangaroa. – A speckled bird; somewhat larger than the Kere-a-rako. Frequents coconut palm blossoms.
Tangaa-‘eo. – The native Wood-pecker; blue above, yellow and white below.
Kere-a-rako. – A small yellow and green song-bird much resembling a canary.
Titi. – A bird living in the rocks and crags. Much relished for food. Cf. Maori Titi, the Mutton-bird. Sanskrit and Hindustani, Titti: Tittiri, the Partridge.
Mokora’a. – The Wild Duck, or rather, a small species of teal, found in abundance round Lake Tiriara.
Kauā. – A sea-bird.
Rakoa. – A sea-bird.
Torea. – A sea-bird.
Kotuku. – The Blue Heron.
Kakaia. – A beautiful small white tern or sea-gull.
Kotaa. – The Frigate or Boatswain Bird. Cf. Samoa, A ta fu,; id. Fijian, Kandavu; id. Uleai (W. Carolines) Kataf; id. Sonserol (S. W. Caralises) Gatyava; id. Cf. Sanskrit Gandharva, a celestial messenger: angel.
Tavake. – The Tropic Bird (Phaethon). Called in the Marquesas Tavae-ma-te-ve’o, from its two long red tail-feathers. Used in Polynesian head-ornaments. Cf. Ponape Chaok: Chik; id. Cf. Sanskrit Stabaka, Stavaka a peacock’s feather: tuft: plume.
Kara’ura’u. – A sea-bird.
Kururi: Kuriri. – The Sand-Piper.
Karavi’a. – The Long-tailed Cuckoo.
Kura-mō. – A small Parrakeet (on Atiu).” 
The respective scientific names of the birds.:
Pā-Tangaroa. – ?
Tangaa-‘eo. – Todiramphus ruficollaris
Kere-a-rako. – Acrocephalus k. kerearako
Titi. – Pterodroma nigripennis
Mokora’a. – Anas superciliosa
Kauā. – Numenius tahitiensis
Rakoa. – Puffinus lherminieri
Torea. – Pluvialis fulva
Kotuku. – Egretta sacra
Kakaia. – Gygis alba
Kotaa. – Fregata spp.
Tavake. – Phaethon rubricauda
Kara’ura’u. – Procelsterna cerulea
Kururi: Kuriri. – Tringa incana
Karavi’a. – Eudynamis taitensis
Kura-mō. – Vini kuhlii
All of these names can be assigned to actually existing bird species, with one exception – the first name.
So which species is hiding behind the name Pā-Tangaroa?
This is actually a rather unusual name for a Polynesian bird, and the reference to Tangaroa, one of the most important Polynesian gods, is very interesting. Perhaps a bird with such a name was also considered God-like or sacred, or at least as being tapu.
The description of this bird: speckled and slightly larger than the Kerearako (i.e. larger than 16 cm), often found on coconut flowers, fits a star of the genus Aplonis quite well, in fact it suits this genus more than any other genus in question.
So there was almost certainly once a star of the genus Aplonis that lived on the island of Mangaia, and its subfossil bones may sooner or later be discovered; the question is, did the species survive long enough that locals could at least remember that it was called Pā-Tangaroa? Given that research into the fauna and flora of the Cook Islands didn’t begin until the early 20th century … it is entirely possible!
I should also mention that this listing, which dates back to 1920, already mentions the Cook Island reed warbler (Acrocephalus kerearako Holyoak), which was not officially discovered until 1973 (and described a year later). 
 F. W. Christian: List of Mangaia birds. The Journal of the Polynesian Society 29(114): 87. 1920
 D. T. Holyoak: Undescribed land birds from the Cook Islands, Pacific Ocean. Bulletin of the British Ornithologists’ Club 94(4): 145-150. 1974