The Nauru reed warbler is potentially threatened by introduced predators and habitat loss, and its small range means that it could be vulnerable to chance occurrences, such as tropical cyclones.

Reports of a similar warbler from nearby islands suggest that it might previously have been found elsewhere, but was driven to local extinction by introduced cats.

The akros part of the name may have been given through confusion with acutus, and taken to mean "sharp-pointed", referring to the angular head shape typical of this genus.

[1][8] Though the Nauru reed warbler is generally accepted as a species, some authorities, such as H. E. Wolters in Die Vogelarte der Erde (1980) and Howard and Moore in A Complete Checklist of the Birds of the World (1991), have considered it a subspecies of Acrocephalus luscinius, the nightingale reed warbler.

[7] A 2009 phylogenic study of the family Acrocephalidae did not include this species,[12] and as recently as 2010 its relation with other members of the genus was unknown.

The entirety of the upperparts are dark brown, with the rump and uppertail coverts slightly brighter than the tail and mantle.

Close inspection of the wing reveals darker centres to both the greater coverts and tertial feathers.

Its face shows little contrast, as the ear coverts, crown, nape, chin and throat are all a similar shade of pale brown.

The lores are a dark brown, and there is a pale, creamy supercilium, or "eyebrow", extending from the beak to the ear coverts, which are a cinnamon-brown, darkening and merging with the nape.

On the Marshall Islands, traditional stories refer to a small bird, known in Marshallese as annañ, anang or annãng.

Though no physical descriptions exist of the species, it has been described as butterfly-sized, pleasant-smelling and as living among rocks on the shores of north-western islands.

Based on descriptions of birds seen on Jaluit, Paul Schnee hypothesised that the annañ may have been a Nauru reed warbler.

Eggs have variously been reported in December and July, and ornithologist A. Pearson suggested that the species may nest all year round.

[7] Six species of dragonfly have been observed on the island: Ischnura aurora, Anax guttatus, Diplacodes bipunctata, Pantala flavescens, Tholymis tillarga and Tramea transmarina.

In open areas, the birds were observed moving across the ground, "occasionally grasping a presumed prey item".

[7] The IUCN lists the species as "Vulnerable", because "its very small range leaves it susceptible to chance events, such as cyclones and the introduction of alien predators.

[1] In 2001, it was observed that the removal of the phosphate deposits on the island meant that the vegetation was decreasing, presenting a potential threat to the species.

[22] In 2008, however, Buden claimed that "habitat degradation and loss of native forest via mining operations has apparently had no major adverse effects on the population.

[23][24] For conservation purposes, the IUCN recommends regular surveys of the population and the establishment of a monitoring programme through training local people.