Norfolk boobook
Illustration by Henrik Grönvold
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Strigiformes
Family: Strigidae
Genus: Ninox
Species:
N. novaeseelandiae
Subspecies:
N. n. undulata
Trinomial name
Ninox novaeseelandiae undulata
(Latham, 1801)

The Norfolk boobook (Ninox novaeseelandiae undulata), also known as the Norfolk Island boobook, Norfolk Island owl or Norfolk Island morepork, is a bird in the true owl family endemic to Norfolk Island, an Australian territory in the Tasman Sea between Australia and New Zealand. It is a subspecies of the morepork (Ninox novaeseelandiae).

Although the taxon is extinct as a pure lineage, its genes live on in the descendants of the hybrid offspring of the last female bird, which was sighted for the last time in 1996.[2] Due to the genetic closeness of the Norfolk and New Zealand moreporks, with the majority of original Norfolk boobook DNA being preserved in modern birds, the subspecies is thus considered extant by the International Ornithological Congress and the EPBC Act despite the hybridization.[3][4][5]

Description

Watercolour by James Stuart, 1839

The Norfolk boobook is very similar in appearance to the New Zealand and Tasmanian boobooks, being a small brown hawk owl with mottled plumage. It is smaller, darker and more reddish in colouring than the Tasmanian boobook, with much spotting.[6] However, it is slightly larger than the nominate subspecies from New Zealand; female boobooks are larger than the males, with New Zealand females comparable in size to Norfolk Island males, a factor which gave rise to sexing difficulties with hybrid birds in the conservation management program.[7]

Habitat

The owl inhabits the island's subtropical rainforest, which was largely cleared in the 19th century following human settlement. Most of the remaining forest lies within the small (4.65 km²) Mt Pitt section of the Norfolk Island National Park.

Behaviour

Breeding

Boobooks breed in tree hollows. Recorded clutch sizes from Norfolk Island range from one to three eggs, with two being usual.[8]

Feeding

Boobooks feed on small vertebrates, especially birds and mammals, as well as invertebrates.

Status and conservation

The population of the Norfolk boobook declined with the clearance and modification of its forest habitat, especially the felling of large trees with suitable hollows for nesting in. There was also competition for nest hollows with feral honey bees and introduced crimson rosellas.[9] By 1986 the population had been reduced to a single female bird, named "Miamiti" after a matriarch of the Norfolk Island people.[10] As part of a program to attempt to conserve at least some of the genes of the insular subspecies, two male moreporks of the nominate New Zealand subspecies, Ninox novaeseelandiae novaeseelandiae, were introduced to the island as mates for the female. The males were sourced from the New Zealand subspecies rather than one of the Australian subspecies as it was discovered that it was more closely related to the Norfolk Island taxon.[11][12] Nest boxes were also provided. One of the introduced males disappeared a year after introduction but the other successfully mated with the female with the pair producing fledged chicks in 1989 and 1990. The original female disappeared in 1996 but, by then, there was a small hybrid population of about a dozen birds. These birds and their descendants continue to exist on the island. By 2018, between 45-50 birds were known, although the population has been inbred and aging with no new recruitment since 2012.[13]

The New Zealand and Norfolk boobooks are considered to be very closely related, with some debate over whether it should even be recognized as a separate taxon; they can only be distinguished by their physical features.[3] For this reason, the International Ornithological Congress does not consider this subspecies to be extinct as it was saved by the hybridization program, despite it no longer surviving as a genetically pure lineage. Genetic analysis indicates that half the nuclear genome and all the mtDNA of the original Norfolk boobook persists in the modern birds, marking it a special case of a taxon that can still be considered extant in a hybrid form. This may be due to the last surviving pure bird being a female, allowing for the mtDNA to be fully passed on.[4][5]

Notes

  1. ↑ "Species Profile and Threats Database Ninox novaeseelandiae undulata — Norfolk Island Boobook, Norfolk Island Morepork, Southern Boobook (Norfolk Island)". Canberra: Department of Agriculture, Water and Environment. Retrieved 2022-08-22.
  2. ↑ Garnett & Crowley, p.365
  3. 1 2 Norman, Janette; Olsen, Penny; Christidis, Les (1998). "Molecular genetics confirms taxonomic affinities of the endangered Norfolk Island Bookbook Owl Ninox novaeseelandiae undulata". Biological Conservation. 86 (1): 33–36. doi:10.1016/S0006-3207(98)00012-3.
  4. 1 2 "Owls – IOC World Bird List". Retrieved 2022-08-24.
  5. 1 2 Garnett, Stephen T.; Olsen, Penny; Butchart, Stuart H. M.; Hoffmann, Ary A. (2011). "Did hybridization save the Norfolk Island boobook owl Ninox novaeseelandiae undulata?". Oryx. 45 (4): 500–504. doi:10.1017/S0030605311000871. ISSN 1365-3008.
  6. ↑ Higgins, p.853.
  7. ↑ Double & Olsen, pp.283-284.
  8. ↑ Higgins, p.866.
  9. ↑ Garnett & Crowley, p.365
  10. ↑ Anon, p.20.
  11. ↑ Double & Olsen, p.283.
  12. ↑ Norman et al, p.33.
  13. ↑ "Norfolk Island boobook owl". Department of Climate Change, Energy, the Environment and Water. 2018.

References

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