Acrocephalus aequinoctialis is endemic to Kiritimati (Christmas Island) and Teraina (Washington) islands in the Northern Line Islands, Kiribati. It was described as 'common' on Kiritimati in 19661, but just 400 individuals were estimated there in 1972 and it was 'scarce in the vicinity of settlement' by 19802. It remained common on Teraina in 19803. It formerly occurred on Tabueran (Fanning), but was apparently extirpated in 1972,
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