Guadalcanal Boobook, Ninox granti, was recently split from N. jacquinoti and is currently assessed to be Vulnerable under criteria B1b(v)c(iv); C2a(ii)b. Endemic to the island of Guadalcanal, Solomon Islands, this species occurs in forest as well as at the forest edge and in forest patches (Dutson 2011). Habitat loss has been relatively low and this species does show some ability to tolerate habitat degradation, but it is currently considered to be declining as a result of habitat loss and coversion (G. Dutson in litt. 2014). The species is not known to be undergoing extreme fluctuations in population size, and the current inclusion of B1b(v)c(iv) and C2b in its Red List criteria string is erroneous.
The population size is currently listed as falling within the range of 2,500-9,999 mature individuals, but the species is described as fairly common (Dutson 2011) and an estimate based on information about congeners suggest that the population size may in fact be larger than this. Home range size for Morepork N. novaeseelandiae, in New Zealand is 3.5-307 ha, with a representative size of 40 ha (Imboden 1975, Pryde and Green 2016, M. Pryde in litt. 2016 per G. Dutson in litt. 2016) and home range size of Southern Boobook, N. boobook, in Australia falls in the range 18 – 206 ha (Olsen et al. 2011). Calling rates of Guadalcanal Boobook have been suggested to be approximately similar to that of these two species in more productive forests (G. Dutson in litt. 2016) and so using an assumption that over half of Guadalcanal represents suitable, inhabited habitat (see e.g. Katovai et al. 2015, G. Dutson in litt. 2016), then the population size of this species may be precautionarily estimated to be 10,000-19,999 mature individuals (G. Dutson in litt. 2016). The species would, therefore, no longer meet the threshold for Vulnerable under criterion C. However, given that the population size of this species approaches the threshold for Vulnerable, it is proposed that this species would warrant listing as Near Threatened under criterion C2a(ii).
We welcome any comments and further information regarding this proposed downlisting, particularly regarding the amount of suitable habitat, as if it may be considered less that stated above this could impact population size estimates and as such the species may warrant retaining as Vulnerable.
Dutson, G. 2011. Birds of Melanesia: Bismarcks, Solomons, Vanuatu and New Caledonia. Christopher Helm, London.
Imboden, C. 1975. A brief radio-telemetry study on Moreporks. Notornis 22: 221-230.
Katovai, E.; Edwards, W.; Laurance, W. F. 2015. Dynamics of logging in Solomons Islands: the need for restoration and conservation alternatives. Tropical Conservation Science 8 (3): 718-731.
Olsen, J.; Downs J. A.; Tucker, T.; Trost, S. 2011. Home-range size and territorial calling of Southern Boobooks (Ninox novaeseelandiae) in adjacent territories. Journal of Raptor Research 45(2): 136-142.
Pryde, M. A.; Greene. T. C. 2016. Determining the spacing of acoustic call count stations for monitoring a widespread forest owl. New Zealand Journal of Ecology 40(1): 100-107.