VU
Christmas Boobook Ninox natalis



Justification

Justification of Red List Category
This species is classified as Vulnerable because its range is restricted to one very small island, it is estimated to have a small population (ca. 1000 individuals) (Garnett et al. (2011) and it may be susceptible to the effects of introduced taxa. It had previously been listed as Critically Endangered but was downlisted following episodic control of the yellow crazy ant Anoplolepis gracilipes, a possible threat which may be ongoing.

Population justification
The population is estimated at c.1,000 mature individuals (Hill and Lill 1998, D. James in litt. 2004, 2005, Garnett et al. 2011).

Trend justification
No hard data are available, but a negligible decline or stable trends are suspected because the species appears to adapt fairly well to secondary habitats. 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).

Distribution and population

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. The population was estimated at 562±105 pairs in 1995 and c.1,000 individuals in 2004 (Hill & Lill 1998, S. Garnett in litt. 2004, D. James in litt. 2004, D. James in litt. 2005). It is suspected to have declined in the recent past, although numbers are now thought to be more or less stable, with Hill and Lills (1998) estimate still thought to be the most accurate available (James and McAllan 2014). Based on sampling in 2011, Low & Hamilton (2013) considered that estimates of 1000 mature individuals ‘may be a significant overestimation’. However, a substantial monitoring program undertaken annually for the period 2012-2015 reported no significant trend, and estimated a population size of between 300 and 3000 individuals (Parks Australia: Woinarski & Legge unpubl.)

Ecology

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. Super-colonies of the invasive yellow crazy ant may reduce invertebrate prey availability (J. Woinarski in litt. 2016).

Threats

Ongoing forest clearance for phosphate extraction has destroyed 25% of available habitat. In 2007, some significant patches of mature secondary forest were cleared for mining (D. James in litt. 2007). A possible threat is the introduced yellow crazy ant Anoplolepis gracilipes which forms super-colonies over much of the island, and is episodically controlled (Woinarski in litt. 2016).  If allowed to spread uncontrolled, ant super-colonies may prey directly on nestlings (although there is no evidence that this is a threat) and alter island ecology by killing the dominant life-form, the red crab Gecaroidea natalis, which otherwise inhibits understorey plant growth and the spread of weeds by eating the seeds and seedlings of both native and invasive species (P. Green and D. O'Dowd in litt. 2003, S. Garnett in litt. 2003, D. James in litt. 2007): this may reduce habitat quality for hawk-owls (Woinarski in litt. 2016). The ants also farm scale insects, causing canopy die-back, which in turn promotes weed growth and further alters forest structure (D. James in litt. 2007). The species may also be affected by the pesticide Fipronil used for ant control, but this remains unproven. Black Rats Rattus rattus, which are affecting some other bird species on Christmas Island, are also likely to kill birds and reduce nesting success (Garnett et al. 2011). Climate change is considered a future threat, with this species having low exposure but high sensitivity (Garnett & Franklin 2014).


Conservation actions

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 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).  

Conservation Actions Proposed
Control the abundance and spread of A. gracilipes. Rehabilitate rainforests in priority areas after the cessation of mining activities. Negotiate with all landowners to ensure protection of primary forests outside the national park. Form a recovery team and implement the recovery plan. Conduct a community education programme. Use established methods to monitor the population.

Identification

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.

Acknowledgements

Text account compilers
Benstead, P., Garnett, S., McClellan, R., Taylor, J., Allinson, T, Symes, A., North, A.

Contributors
Woinarski, J., James, D., Blyth, J., Low, T., O'Dowd, D., Garnett, S., Green, P., Hennicke, J.


Recommended citation
BirdLife International (2021) Species factsheet: Ninox natalis. Downloaded from http://www.birdlife.org on 24/10/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 24/10/2021.