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Christmas Boobook Ninox natalis

Justification
This species is classified as Vulnerable because it has a very small range on one very small island, and it is susceptible to the effects of introduced taxa. It had previously been listed as Critically Endangered but was downlisted following control of the yellow crazy ant Anoplolepis gracilipes, which is ongoing.

Taxonomic source(s)
Christidis, L.; Boles, W. E. 2008. Systematics and taxonomy of Australian birds. CSIRO Publishing, Collingwood, Australia.
del Hoyo, J.; Collar, N. J.; Christie, D. A.; Elliott, A.; Fishpool, L. D. C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Barcelona, Spain and Cambridge UK: Lynx Edicions and BirdLife International.
Norman, J. A.; Christidis, L.; Westerman, M.; Hill, F. A. R. 1998. Molecular data confirms the species status of the Christmas Island Hawk-owl Ninox natalis. Emu 98: 197-208.

Taxonomic note
Ninox squamipila, N. hypogramma, N. hantu and N. forbesi (del Hoyo and Collar 2014) were previously lumped as N. squamipila following Norman et al. (1998), and before then were also lumped with N. natalis as N. squamipila following Sibley and Monroe (1990, 1993).

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.

Distribution and population
Ninox natalis is restricted to Christmas Island (to 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 560±100 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.

Population justification
The population is estimated at c.1,000 individuals (S. Garnett in litt. 2004, D. James in litt. 2004, 2005), roughly equivalent to 670 mature individuals.

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).

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). They nest 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.

Threats
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). Also in 2007, a new application to mine a 250 ha area of rainforest (P. Green in litt. 2007) was turned down (J. Hennicke in litt. 2007), but has since gone to appeal (D. James in litt. 2007). A possible threat is the introduced yellow crazy ant Anoplolepis gracilipes which formed super-colonies during the 1990s and spread rapidly to cover about 25% of the island or c.3,400 ha, but in 2002 it was controlled over about 2,900 ha. Since then a number of supercolonies have been re-established (D. James in litt. 2007), and in 2006, the ants were regarded as widespread and patchily common (T. Low in litt. 2006). 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). 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 scale at which these processes occur is uncertain (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). Disease is another potential threat, for which two established exotic sparrows could act as conduits between domestic chickens and wild birds (D. James in litt. 2007).




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 prevents clearance of primary rainforest and in theory requires permits to clear regrowth. However, in reality regrowth is still cleared without permits (D. James in litt. 2007). A draft recovery plan has been prepared.  Anoplolepic gracilipes, Yellow crazy ant supercolonies are altering forest composition and dynamics and potentially reducing insect populations (the primary prey of the Hawk-owl). A control programme for A. gracilipes has been successfully initiated since 2000 and has effectively eliminated the ant from 2,800 ha of forest (95% of its former extent) (P. Green and D. O'Dowd in litt. 2003). Monitoring of the problem continues and hand-baiting measures have been ongoing. Aerial baiting commenced in September 2002 and proved to be successful against major colonies (Olsen 2005), eliminating over 98% of ants (D. James in litt. 2007). However, the ants have since recovered (D. James in litt. 2007). The ants remained persistent in 2006, and perpetual baiting may be the only means of controlling them. 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 has been suggested, 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 stabalize (S. Garnett in litt. 2005), although there is no evidence of past declines or fluctuations (D. James in litt. 2007).  However, "Pending control of yellow crazy ants, establishment of a captive population of the hawk-owl was recommended (DEH 2003)." (http://www.environment.gov.au).  An action plan has been in place since 2004.
Conservation Actions Proposed
Control the abundance and spread of A. gracilipes and establish a precautionary captive breeding population. 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.

Related state of the world's birds case studies

References
Garnett, S. T.; Crowley, G. M. 2000. The action plan for Australian birds 2000. Environment Australia, Canberra.

Garnett, S.T., Szabo, J.K. and Dutson, G. 2011. The Action Plan for Australian Birds 2010. CSIRO Publishing, Collingwood.

Hill, F. A. R.; Lill, A. 1998. Density and total population estimates for the threatened Christmas Island Hawk-owl Ninox natalis. Emu 98: 209-220.

Norman, J. A.; Christidis, L.; Westerman, M.; Hill, F. A. R. 1998. Molecular data confirms the species status of the Christmas Island Hawk-owl Ninox natalis. Emu 98: 197-208.

Further web sources of information
Australian Govt - Action Plan for Australian Birds 2000 - Recovery Outline

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

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

Recommended citation
BirdLife International (2014) Species factsheet: Ninox natalis. Downloaded from http://www.birdlife.org on 25/12/2014. Recommended citation for factsheets for more than one species: BirdLife International (2014) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 25/12/2014.

This information is based upon, and updates, the information published in BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004) Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.

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Additional resources for this species

ARKive species - Christmas hawk-owl (Ninox natalis) 0

Key facts
Current IUCN Red List category Vulnerable
Family Strigidae (Typical Owls)
Species name author Lister, 1889
Population size 670 mature individuals
Population trend Stable
Distribution size (breeding/resident) 140 km2
Country endemic? Yes
Links to further information
- Additional Information on this species