Data Zone
Justification of Red List category
This species is classified as Vulnerable because it has a very small population size restricted to a single island, estimated to be less than 1,000 mature individuals.
Population justification
About 342 mature Christmas Island Boobooks were thought to be present on the island in 2016 based on call playback at 135 sites (Morcombe 2016). This is higher than suggested by Low and Hamilton (2013) who suggested a population size in the range 1-100 pairs based on call playback surveys, but lower than the estimates of Hill and Lill (1998), who postulated a population of 820–1,200 birds based on the areas occupied by six radio-tracked individuals in the 1990s. Based on these estimates, Macgregor et al. (2021) estimate the total number of mature individuals to be in the range 240-1,200, with a best estimate of 340.
Trend justification
Control of the ants may have allowed the species' population to stabilise in the past (S. Garnett in litt. 2005), although there is no evidence of past declines or fluctuations (D. James in litt. 2007). There is currently no evidence of a continuing decline. Reporting rates and occupancy at 105 sites in 2006, annually from 2012 to 2017, and in 2019 are suggestive of an overall stable population (James and McAllan 2014, Director of National Parks unpublished, Legge and Woinarski unpublished).
Ninox natalis is restricted to Christmas Island (Australia) in the Indian Ocean. The species is present throughout the island, with highest densities occurring in primary forest and the lowest in regrowth after mining.
It occupies permanent territories in all habitats on the island to 360 m (D. James in litt. 2007), although it is absent from mined sites that have not been rehabilitated. The species does however occupy re-established vegetation of over c.10 years in age on old mining sites (D. James in litt. 2007). It nests in tree hollows in closed forest 30–40 m high with emergent trees up to 45 m tall, predominantly with Syzygium nervosum, Planchonella nitida, and Hernandia ovigera as canopy trees (Garnett et al. 2011). Its diet consists primarily of insects supplemented with small vertebrates, possibly including the introduced black rat Rattus rattus, cockroaches and geckos (Kent and Boles 1984). Super-colonies of the invasive yellow crazy ant may reduce invertebrate prey availability (J. Woinarski in litt. 2016).
Historically, phosphate mining and other development removed approximately 25% of the boobook's habitat, which was thought to have led to a proportional decline in owl numbers (Stokes 1988). At the time of writing, no clearing of the island's old-growth forest (primary vegetation) has been permitted since 1988. Birds use damaged habitat for feeding if not for nesting (James and McAllan 2014). Further removal of vegetation, if it were to occur in the future, could be a major threat to the boobook and would potentially push this species into a higher threatened category because the population is so small. Control of black rats Rattus rattus could cause secondary mortality of owls (Beeton et al. 2010, Lohr and Davis 2018). A possible threat is the introduced yellow crazy ant Anoplolepis gracilipes which forms super-colonies over much of the island, and is episodically controlled (J. Woinarski in litt. 2016). Climate change is considered a future threat, with this species having low exposure but high sensitivity (Garnett and Franklin 2014).
Conservation Actions Underway
CITES Appendix II. A national park was created in 1980, and has since been extended to cover more than 60% of the island (D. James in litt. 2007). A lease agreement has been established with the mining company which constrains clearance of primary rainforest and in theory requires permits to clear regrowth. A recovery plan has been prepared (Hill 2004). Yellow crazy ant Anoplolepic gracilipes supercolonies are altering forest composition and dynamics and potentially reducing insect populations (the primary prey of the owl). A control programme for A. gracilipes has been initiated episodically since 2000 (P. Green and D. O'Dowd in litt. 2003). The bait used so far (Fibronil) is known to be toxic to invertebrates, including crabs, and although alternatives have been trialled, an effective replacement has not been found (D. James in litt. 2007). Control of the scale bugs that the ants tend for their sugar secretions is proposed, in order to reduce this food supply (T. Low in litt. 2006, D. James in litt. 2007). Control of the ants may have allowed the species's population to stabilise (S. Garnett in litt. 2005), although there is no evidence of past declines or fluctuations (D. James in litt. 2007).
26-29 cm. Small, rufous-brown hawk-owl. Sexes similar, female slightly larger. Rufous-brown upperparts. Rows of small, white spots on secondary coverts, scapulars and tertials. Darker brown barring on remiges and tail. Underparts barred rufous and white. Underwing rufous-brown on coverts, barred light and dark grey on remiges. Yellow legs and feet. White lores, short supercilia and chin. Bright yellow iris in small, dark disc. Juvenile downier with whitish underside and head. Voice Double-noted hoot boo-book, second note usually lower in pitch than first. Juvenile begging call, high-pitched trill.
Text account compilers
Vine, J.
Contributors
Blyth, J., Garnett, S., Green, P., Hennicke, J., James, D., Low, T., O'Dowd, D., Woinarski, J.C.Z., Allinson, T, Elliott, N., Taylor, J., North, A., Symes, A., McClellan, R. & Benstead, P.
Recommended citation
BirdLife International (2024) Species factsheet: Christmas Island Boobook Ninox natalis. Downloaded from
https://datazone.birdlife.org/species/factsheet/christmas-island-boobook-ninox-natalis 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.