Threatened Species Strategy – Year 3 Priority Species Scorecard (2018) Norfolk Island Boobook Ninox novaeseelandiae undulata Key Findings Norfolk Island Boobook Owls nearly became extinct in the 1980s, following extensive historic clearing of habitat and nesting trees. Very few natural nesting sites remain on the island and the small population of owls is now highly inbred. Conservation efforts have focused on securing nest sites and culling nest competitors, such as introduced rosellas, however there has been no successful breeding observed since 2012. Photo: Amy Svendsen Significant trajectory change from 2005-15 to 2015-18? No, population currently stable, although outlook is poor. Priority future actions • Research to determine whether genetic constraints or poor nestbox placement are the primary reasons for the apparent lack of breeding • Intensive crimson rosella and rat control to reduce the risk of predation and competition • Provide and maintain rat proof nest boxes for roosting and breeding both within the national park and community wide where breeding birds are known to occur Full assessment information Background information 2018 population trajectory assessment 1. Conservation status and taxonomy 8. Expert elicitation for population trends 2. Conservation history and prospects 9. Immediate priorities from 2019 3. Past and current trends 10. Contributors 4. Key threats 11. Legislative documents 5. Past and current management 12. References 6. Support from the Australian Government 13. Citation 7. Measuring progress towards conservation The primary purpose of this scorecard is to assess progress against achieving the year three targets outlined in the Australian Government’s Threatened Species Strategy, including estimating the change in population trajectory of 20 bird species. It has been prepared by experts from the National Environmental Science Program’s Threatened Species Recovery Hub, with input from a number of taxon experts, a range of stakeholders and staff from the Office of the Threatened Species Commissioner, for the information of the Australian Government and is non-statutory. It has been informed by statutory planning documents that guide recovery of the species, such as Recovery Plans and/or Conservation Advices (see Section 11). The descriptive information in this scorecard is drawn from Threatened Species Scientific Committee (2016) unless otherwise noted by additional citations. The background information aims to provide context for estimation of progress in research and management (Section 7) and estimation of population size and trajectories (Section 8). 1 Information current to December 2018 Threatened Species Strategy – Year 3 Priority Species Scorecard (2018) 1. Conservation status and taxonomy Conservation status 2018 Taxonomy: N. n. albaria of Lord Howe Island is Extinct. Nominate IUCN Critically Endangered subspecies from New Zealand is Least Concern, as is the species. EPBC Endangered The population on Norfolk Island retains some genes from the island Endemic N. n. undulata and, because of the limited nature of the intentional hybridisation; it is argued that the taxon does not meet the criteria for Extinct. 2. Conservation history and prospects The Norfolk Island Boobook declined to a single female in the 1970s. Before she died in 1996 she had bred with one of two introduced males of the New Zealand subspecies and numbers increased until there were estimated to be as many as 50 individuals (Olsen 1996). However, despite removal of many competitors for the few hollows suitable for breeding, no reproduction has been confirmed since 2012 (M.Wilson pers.comm.) and the population is again in great peril. 3. Past and current trends The rarity of the owl was first appreciated in the 1960s and from the 1970s just one bird was heard calling. By the 1980s it was realised only a single female survived. Two males of the only other extant subspecies, from New Zealand, were introduced and she mated with one of them (Olsen 1996). The offspring from that mating, which are inevitably highly inbred, were thought to number 45-50 in 2017. However, there appears to have been no successful breeding since 2012, despite the active maintenance of nine nestboxes from 2015-2018 and the active culling of nest competitors. There is no information on why this is so. Monitoring (existing programs): Population surveys undertaken by Norfolk Island National Park (NINP) staff and community volunteers in 2016 and 2017 used listening locations and call play-back. There is an unpublished report from 2016 held by NINP and one from 2017 in preparation. Nine operational nestboxes placed at 7 m in apparently suitable trees in 2016 are maintained free of pests and checked regularly for activity. Population trends: Tables 1 and 2 summarise the overall trend and status of the Norfolk Island Boobook. The information provided in these tables is derived from Threatened Species Scientific Committee (2016), with some amendments from contributing experts based on new information. 2 Information current to December 2018 Threatened Species Strategy – Year 3 Priority Species Scorecard (2018) Table 1. Summary of the available information on NI Boobook distribution and population size, and (where possible) trend estimates between 2015 and 2018 for each parameter. Published 2015 2018 Population parameters Confidence in estimates baseline Estimate Estimate Extent of Occurrence 12 km2 35 km2 35 km2 High Area of Occupancy 8km2 30 km2 30 km2 High Predominantly occurred in the Mt Pitt region of the NINP (460 ha) in 1996 (10 Dates of records and methods females, 7 males of which 3 were juvenile) but birds present over most of island used during community owl surveys and call play-back in 2014, 2016 and 2017, so probably the same in 2015 and 2018. No. mature individuals 40 45-50 45-50 Low Any other measure of relative n/a n/a n/a n/a abundance (specify) No. of subpopulations 1 1 1 High No. of locations 1 1 1 High High. Derived from latest global analysis Generation time 4.7 n/a n/a by BirdLife International Table 2. Estimated recent and current population trend for the NI Boobook. Est. % of 1988- Confidence 2015- Confidence Sub- populati 2015 in 1988- 2018 in 2015- Details population on trend 2015 trend trend 2018 trend Numbers were closely monitored from 1988-1999 and all offspring banded. There is high confidence that numbers increased until 1999. The population was perhaps stable between 1999 and 2007. There is low confidence about trends in numbers Whole 100 Very high Low until the surveys in 2016 and 2017 population suggesting numbers were 45-50 at that time with detailed knowledge of the location of clusters of records. A failure to reproduce during this time means it is highly likely that numbers declined if some old birds died but surveys could not detect the change. KEY: Improving Stable Deteriorating Unknown Confidence Description High Trend documented Medium Trend considered likely based on documentation ? Low Trend suspected but evidence indirect or equivocal 3 Information current to December 2018 Threatened Species Strategy – Year 3 Priority Species Scorecard (2018) 4. Key threats The threats listed here are derived from Threatened Species Scientific Committee (2016), with some amendments from contributing experts based on new information. Note that this is not a list of all plausible threats, but a subset of the threats that are likely to have the largest impact on populations. Farming and forestry Extensive clearance of vegetation for agriculture and felling of large trees destroyed most suitable nest sites on Norfolk Island, making competition for remaining sites intense. Thus, although the land clearance has stopped, the legacy continues to have a major impact on the owls’ prospects through lack of hollows (Garnett et al. 2011). Nest competitors Crimson Rosellas (Platycercus elegans), and to a lesser extent Common Starlings (Sturnus vulgaris) and sometimes feral bees (Apis melifera), all compete for scarce hollows. All are introduced to Norfolk Island. Crimson Rosellas sometimes expel established Boobook pairs from hollows. Common Starlings fill hollows with material that render hollows unsuitable for Boobooks. Bees, rarely, can kill owls if a swarm invades an occupied nest, and thereafter prevent owls from using the hollow (Garnett et al. 2011). Guava, olives and other feral weeds It has been hypothesised that habitat consisting primarily of a dense understorey created by red guava (Psidium spp.), African olive (Olea europaea), wild tobacco (Solanum mauritianum) and lantana (Lantana camara) is likely to support only half the density of owls when compared to remnant forest (Olsen 1997) It is estimated that the island consists of 190 ha of remnant forest, 200 ha of weed- invaded forest and 1500 ha of cultivated and urban areas (Olsen 1997). Lack of genetic variability The population of Norfolk Island Boobook Owls is highly inbred and smaller clutch sizes suggest inbreeding depression (Garnett et al. 2011). Potentially this could be behind the apparent lack of breeding in recent years, although one would expect the owls to attempt to breed even if their eggs were infertile, and some birds that successfully bred previously must still be alive. A highly skewed sex ratio towards females, which may also be a problem (Olsen 1997) would also represent a lack of genetic variability. Climate change, drought and bushfires Some modelling suggests a drying of the island’s climate, perhaps rendering both the eucalypt plantation and the adjacent national park rainforest vulnerable to uncontrolled fire (Garnett and Franklin 2014). The impacts of the major threats are summarised in Table 3. 4 Information current to December 2018 Threatened Species Strategy – Year 3 Priority Species Scorecard (2018) Table 3. The major threats facing the NI Boobook and their associated impact scores. CURRENT THREAT IMPACT Threat Timing Extent Severity 1. Farming and forestry Continuing/ongoing >90% of range Not negligible but <20% 2. Nest competitors Continuing/ongoing >90% of range 20-29% 3. Weeds Continuing/ongoing 50-90% of range Not negligible but <20% 4.