Justification of Red List category
Although this species has a very small population and range on a single island, the population is estimated to be stable. There are currently no plausible threats that could cause the species to become threatened within a short time. The species is therefore listed as Least Concern.
Inside Norfolk Island National Park, 3,830 (95% CI 2,650-5,540) mature individuals were estimated in 2009 (Dutson 2013), followed by a higher estimate of 6,305 (95% CI 5,166-8,583) in October 2019. Following Nance et al. (2021), the population size of the whole island is therefore set to 3,800-8,000 mature individuals, with a best estimate of c.5,000.
Historically, c.1600 pairs were estimated to persist in 1988 and 1997 (Robinson 1988, 1997). A larger estimate was made in 2009, when 3,830 (95% CI 2,650-5,540) were thought to exist in the national park (Dutson 2013), while an even more recent estimate (6,305; 95% CI 5,166-8,583) from 2019 suggests the population may have increased further (Nance et al. 2021). However, each of these estimates was born from differences in survey technique, such that direct and robust comparisons are not possible. Nonetheless, a decline is considered very unlikely, and the species is probably increasing in abundance (Nance et al. 2021).
The species is endemic to Norfolk Island, Australia, where it occurs throughout the island. It has not yet recolonised Phillip Island, if indeed it ever occurred there (Schodde et al. 1983). There have been recent records from many sites outside the boundaries of Norfolk Island National Park in the last decade (BirdLife Australia 2020, eBird 2021).
It is found only in remnant areas of tree or shrub growth on the island, such as rainforest, thicket, gardens and white oak pasture, and is common in weedy forest dominated by the exotic red guava Psidium cattleianum and African olive Olea africana but at a density about half that in native forest. It is scattered and much less common in patchy forest and scrub away from the national park.
Most remaining forest is now protected within Norfolk Island National Park or local government reserves. The most significant known threat is predation by black rats Rattus rattus and Pacific rats Rattus exulans which cumulatively caused 31% of monitored gerygone nests to fail in 2018 and 2019 (A.H. Nance, R.H. Clarke unpublished, in Nance et al. 2021). Gerygones also coexist with cats Felis catus. Inside the park, there is ongoing rodent control; predator control outside of the national park is limited. Current evidence suggests that these predators are not driving population decline.
Conservation Actions Underway
Most remaining habitat protected within reserves. Cat trapping and rat baiting occurs regularly. Restoration of native vegetation in areas from which weeds have been removed. Preliminary work to restore habitat outside reserves.
Conservation Actions Proposed
Continuing monitoring the population size. Develop new techniques and strategies for eradicating or controlling rats and controlling cats on Norfolk Island, including methods for targeting rats in trees. Rats and cats should be eradicated or controlled to reduce their impact on native species, including G. modesta. Increase restoration of habitat outside reserves.
9-10 cm. Small, dull-coloured warbler. Dull grey-brown above and whitish below, greyer on face and flanks. Sexes similar. Slender, longish, black bill. White line from base of bill, above dark lores, over eyes. Broken white orbital ring. Tail has indistinct darker subterminal band with white spots except on central feathers. Juvenile more yellow, especially on throat. Similar spp. White-eyes Zosterops spp. are larger with prominent white eye-ring, more yellow or green overall and with differing voice. Voice Warble, rising and falling in pitch.
Text account compilers
Berryman, A., Garnett, S., Vine, J.
Christian, M., Holdaway, R. & Ward, R.
BirdLife International (2023) Species factsheet: Gerygone modesta. Downloaded from http://datazone.birdlife.org/species/factsheet/norfolk-island-gerygone-gerygone-modesta on 08/12/2023.
Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from http://datazone.birdlife.org on 08/12/2023.