Justification of Red List Category
This species has been downlisted from Endangered following evidence that its population is increasing and is now much larger than previously estimated. It is listed as Near Threatened on the basis that it occupies a tiny range and remains susceptible to stochastic events and the impacts of introduced species, such that it could qualify as threatened within one or two generations.
In 1999, the population was estimated to be no fewer than 150 individuals, and it remained at this level until 2004 at least (A. Cristinacce and C. Jones in litt. 2005). The population has since risen rapidly to number over 3,000 (3,100-3,900) individuals by 2010 (Steward 2010, C. Jones in litt. 2010, V. Tatayah in litt. 2011) and close to 4,000 by 2012 (V. Tatayah in litt. 2012). The population is therefore estimated at 3,000-4,000 individuals, assumed to include c.2,000-2,700 mature individuals. It has been noted that the current methodology for censusing this species (Showler 2002, Steward 2010) was designed for low population densities and could now over-estimate numbers (P. Steward in litt. 2013).
Surveys suggest that the population was stable between 1999 and 2004 (A. Cristinacce and C. Jones in litt. 2005), but has since risen rapidly to number over 3,000 (3,100-3,900) individuals by 2010 (Steward 2010, C. Jones in litt. 2010, V. Tatayah in litt. 2011) and close to 4,000 by 2012 (V. Tatayah in litt. 2012).
Acrocephalus rodericanus, having once been very common on Rodrigues, Mauritius, declined steadily until 1979, when eight pairs and a singleton were counted (but others probably overlooked). Since 1982, there has been a steady increase in its range (C. Jones in litt. 2000). In 1999, the population was estimated to number at least 150 individuals (Showler 1999, Showler et al. 2002), and surveys up until 2004 suggested there was no change since then (A. Cristinacce and C. Jones in litt. 2005); however, the population has since risen extremely rapidly to number over 3,000 individuals (3,100-3,900) by 2010 (Steward 2010, C. Jones in litt. 2010, V. Tatayah in litt. 2011, 2012).
It is a territorial insectivore adapted to dense thickets in remaining, largely exotic, vegetation. The low intensity of vegetation cutting by humans appears to promote such dense growth. In 1999, a survey found 78% of the population in habitat dominated by introduced jamrosa Syzygium jambos where the highest densities (2.3 individuals/ha) are found (Showler 1999). The species is also known at lower densities (0.5/ha) in plantations of Swietenia, Tabebuia and Araucaria sp. However other factors, incompletely understood, greatly influence its distribution as demonstrated by the areas of apparently suitable habitat as yet uncolonised (Showler et al. 2002). Restored native forests were found to support the highest densities of the species (Steward 2010). It may breed in groups, as while it usually breeds in pairs there is one report of 4 individuals on a territory, with 3 helping at the nest (Cheke 1987). It lays 3-5 eggs, with the main breeding season September to March (Safford 2013), although only 1-2 chicks may be successfully raised (Safford 2013).
Timber harvesting, subsistence farming and feral livestock have reduced the native habitat to savanna with scattered trees. Currently, the main threat is predation and/or competition from introduced animals such as rats and feral cats (Showler et al. 2002). Sustained periods of drought (reducing invertebrate levels), cyclones, and the destruction and further degradation of remaining suitable habitat are additional problems (Showler et al. 2002). It has survived alongside the Black Rat Rattus rattus for a long time (C. Jones in litt. 2000), but nest predation by this species was believed to be a major factor suppressing its population recovery (Showler et al. 2002). In addition, the fledging success of undisturbed nests appears low, possibly due to food availability (Showler et al. 2002). Human disturbance may be an additional problem at some localities (Showler 1999).
Conservation Actions Underway
Habitat protection and reforestation, spurred by the need for watershed protection, have been key to the recovery of this species, aided by the recent absence of catastrophic cyclones. Much reforestation has involved exotic trees, although native ecosystem rehabilitation has been started at some sites, including nearby islands and the two Conservation Management Areas: Grande Montagne and Anse Quitor (both 0.1 km2). Sites are fenced to exclude grazing animals and woodcutters, exotic plants removed and native species replanted. There has been an accompanying public awareness campaign (Safford 2001). A probable decline in agriculture may have also contributed to habitat availability and the recovery of the species (P. Steward in litt. 2013).
13.5 cm. Medium-sized, drab warbler. Uniformly olive-brown upperparts with paler, yellowish-buff underparts. Long bill with pink lower mandible. Erect crown feathers impart crested appearance. Voice Harsh, chattering alarm call, soft, melodic song. Hints Tail habitually jerked up and down.
Text account compilers
Ekstrom, J., McClellan, R., Pilgrim, J., Shutes, S., Symes, A., Taylor, J., Warren, B., Westrip, J.
Steward, P., Jones, C., Cristinacce, A., Tatayah, V.
BirdLife International (2021) Species factsheet: Acrocephalus rodericanus. Downloaded from http://www.birdlife.org on 22/01/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 22/01/2021.