Justification of Red List category
This species has a very small population size, restricted to Norfolk Island, and has been estimated to be in slow decline primarily as a result of rat predation. The species is therefore assessed as Endangered.
Population justification
There were estimated to be 750 mature Norfolk Island Robins in the park in 2018 (~375 pairs; Dawlings and Clarke unpublished, in Nance et al. 2020) compared with 380–440 (760–880 mature individuals) pairs in 1996 and 520 pairs (1,040 mature individuals) in 1987 (Robinson 1997).
Trend justification
The population was estimated at 1,040 mature individuals in 1987, 760-880 in 1996 and 750 in 2018 (Robinson 1997, Nance et al. 2020). Although the surveys have been at long intervals, a precautionary approach is to assume a gradual decline (Nance et al. 2020). Standard distance sampling approaches do not provide valid results because the robins are attracted to the observer (Dutson 2013). However, an extremely low nest survival rate of 1.7% (using field data collected over the period October–December 2017) in unbaited areas suggested potentially rapid declines. Under a scenario where the allocation of rodent-baiting resources replicates the reduced baiting scheme that operated in the period September–December 2017, the projected probability of persistence was 96% ± 0.01%, however, with a projected population decline of 55% within five years and 50 ± 1.5 individuals remaining after 20 years (Nance et al. 2020). However, as monitoring (to October 2019) does not currently support such steep declines, the species is not thought to qualify for listing as threatened under Criterion A and the species is estimated to be declining gradually (Nance et al. 2020).
This species is endemic to Norfolk Island (to Australia), where it is now largely restricted to the National Park and a few adjacent forested areas (Garnett et al. 2011, Nance et al. 2020). The species gradually disappeared from many sites elsewhere on the island from the 1980s onwards (Schodde et al. 1983, Robinson 1988, Bell 1990). Occasional sightings elsewhere on the island since 2017 probably represent dispersing individuals that are lost to the population (Nance et al. 2020).
Norfolk Island Robins occupy native hardwood forests, with lower densities in areas dominated by Norfolk Island palm Rhopalostylis baueri, exotic African olive Olea africana or exotic eucalypt plantations. They forage for insects in deep litter where a dense understorey has a fairly open ground layer (Robinson 1988) and usually lay two eggs in cup nests near the top of the subcanopy (Robinson 1988, Major 1989).
Since habitat clearance ceased, the main threat is from Black Rats Rattus rattus introduced in the mid 1940s (Robinson 1988) which were the sole identified cause of robin nest failure in a study in 2017. Rats preyed on 75% of nests that were monitored with camera traps and reduced nest success to 17% (Dawlings and Clarke unpublished, in Nance et al. 2020). In unbaited areas, rodent density was twice as high (8.1/ha cf 4.2/ha) and nest survival ~20 times lower (1.6% cf 36.4%) than baited areas. Invasive rodents, especially Black Rats, forage in all forest strata within the National Park. Those individuals that are largely arboreal would avoid rodenticides deployed only on the ground. Rodent abundance may also be inflated by a seasonal abundance of fruit from the invasive guava Psidium spp., which provides unlimited food resources for 3–4 months of the year. Guava bears fruits in autumn meaning elevated rodent numbers experience a reduction in available resources in winter and spring, perhaps placing additional pressure on nesting robins. Cats Felis catus, which were introduced before the 1830s (Moore 1985), may also take some birds (Bell 1990, Director of National Parks unpublished, in Nance et al. 2020). A possible trend towards drier conditions as a result of climate change (Bureau of Meteorology 2019) could lead to deterioration of the robin’s forest habitat, especially as their diet largely consists of invertebrates from the forest floor.
Conservation Actions Underway
Most of the remaining habitat protected within reserves. Cat trapping and rat baiting occurs regularly. Some localised guava control. Native vegetation is being restored in areas from which weeds have been removed.
Conservation Actions Proposed
Develop new techniques and strategies for eradicating or controlling rats and controlling cats on Norfolk Island, including methods for targeting rats in trees (Nance et al. 2020). Identify a cost-effective means of eradicating guava that does not affect the endemic Slender-billed White-eye Zosterops tenuirostris (which feed on the fruits) detrimentally (Nance et al. 2020). Develop improved survey techniques to be able to estimate abundance with high certainty (Nance et al. 2020). Assess the potential for introduction to Phillip Island (Nance et al. 2020). Eradicate or control of rats and cats to reduce their impact on native species (Nance et al. 2020). Maintain management of guava and rehabilitation across the reserves, with the aim of reducing the size of the area dominated by guava (Nance et al. 2020). Increase restoration of suitable habitat outside reserves (Nance et al. 2020).
Text account compilers
Vine, J.
Contributors
Christian, M.
Recommended citation
BirdLife International (2024) Species factsheet: Norfolk Island Robin Petroica multicolor. Downloaded from
https://datazone.birdlife.org/species/factsheet/norfolk-island-robin-petroica-multicolor on 22/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 22/12/2024.