Lord Howe Island Rodent Eradication Project NSW Species Impact Statement February 2017 Appendix F - Masked Owl Package F.1 Draft Masked Owl Eradication Plan F.2 Masked Owl Research Report F.3 Masked Owl Genetics Study DRAFT Lord Howe Island Masked Owl Eradication Plan Prepared for The Lord Howe Island Board By Terence O’Dwyer and Nicholas Carlile Office of Environment and Heritage, P.O. Box 1967, Hurstville, NSW 2220. June 2016 Background and justification Masked Owls (Tyto novaehollandiae), along with a number of other owl species, were introduced to Lord Howe Island in the 1920s to help control introduced Ship Rats (Rattus rattus). Of the owl species introduced, only Masked Owls remain on the island and the species is now considered to be a pest. A rodent eradication plan (REP) for Ship Rats and House Mice (Mus musculus) is proposed for Lord Howe Island in winter 2017. Concurrent with the REP, the Lord Howe Island Board proposes to also eradicate Masked Owls. Milledge (2010) previously performed an extensive study on the distribution and habitat use, movements, home ranges, population size, roost sites, and diet of the Lord Howe Island Masked Owl population and that research, as well as a recent workshop involving proponents for the owl eradication, are used to inform this currently proposed Masked Owl eradication plan (MOEP). It was previously thought that Lord Howe Island Masked Owls were sourced from Tasmania (Tyto n. castanops), where the species is listed as threatened under Tasmania’s Threatened Species Protection Act 1995. However, recent genetic studies have shown that at least some of the Lord Howe Island Masked Owl ancestry comes from the south-eastern Australian mainland (Tyto n. novaehollandiae) and not solely from Tasmania (Hogan et al 2013). While Masked Owls are also listed as threatened in NSW (Threatened Species Conservation Act 1995) and Victoria (Flora and Fauna Guarantee Act 1988), the Lord Howe Island Masked Owl is of limited conservation value because translocations to either the Tasmanian or mainland populations would compromise the genetic integrity of the recipient populations. Currently, introduced rats and mice form the Lord Howe Island Masked Owl’s main prey base but the owls also prey on native species including the Black-winged Petrel, the White Tern, the Sooty Tern and the Lord Howe Woodhen (Milledge 2010). Following rodent eradication programmes in other locales, predators of rats have maintained their previous abundance by switching to other available prey (e.g. Murphy and Bradfield 1992). It is feared, therefore, that if rats and mice are eradicated from Lord Howe Island, owls will switch their prey base to native species (Milledge 2010). Thus, it is imperative, that owls be eradicated prior to and concurrently with, the rodent eradication. This MOEP will consist of several components including pre- and post-REP owl surveys, owl trapping and a shooting programme. These components are outlined below. The opportunity to, and utility of, translocating owls is also briefly discussed. Management of the programme It is recommended that a Project Manager be appointed and a Technical Advisory Group (TAG) be established to support the programme. The TAG will need to include expertise on masked owl ecology and bird capture as well as eradication expertise and local knowledge of the island. A detailed Operational Plan should be produced that clearly indicates who is responsible for decision- making and outlines specific roles within the project. The TAG will advise the Project Manager and provide input into and finalise the Operational Plan. The project manager and TAG should be appointed as soon as is practicable. Pre- and post-REP population estimates Pre-REP surveys will be performed to estimate the current distribution and size of the owl population and to provide a measure of the number of owls, general location of roost sites, and key areas that will be required to be targeted in the subsequent shooting programme. Simultaneous point surveys will follow the methods performed previously by Milledge (2010). Briefly, locations of point surveys will be selected to cover the slopes of the southern mountains and the northern hills of the island. The aim of the point surveys will be to provide a measure of owl density in two important areas of habitat. Measures of owl density will be then be extrapolated to the remainder of the island to inform an overall estimate of population size. The survey method will comprise a 45 minute listening period from dusk (with an agreed start time prior to the survey). Prior to the REP, the simultaneous point surveys will be performed every three months until baiting occurs, with the first survey to be performed as soon as is practicable. Surveys will then continue to be performed once every three months for two years in line with the post-eradication rodent monitoring. Personnel A total of sixteen people will be required to perform point surveys at eight locations across the island. Each team of two will have at least one person who is familiar with the survey method, call playback technique and the calls of the Masked Owl. Volunteers from within the Lord Howe community will be sought to perform these surveys where possible but people from off the island may also be involved. Acoustic monitoring Remote acoustic monitoring devices will be used to constantly monitor owl calls in remote areas of the island. The deployment and recovery of three units in selected locations throughout 2017 can inform both the population monitoring and eradication effort. Acoustic monitoring devices would be rotated throughout the island on a monthly basis (for recovery of recordings and refreshing of power source). The recovery of information from the recordings can either be through intensive replaying or the application of call-recognition software. Eradication Methods Secondary poisoning and trapping There is the potential for a number of owls to succumb to secondary poisoning during the REP as a result of preying on rodents that have consumed brodifacoum. However, it cannot be presumed that all owls will die in this manner; poisoned rodents may be unavailable in some areas, and because rodenticides are currently used on Lord Howe Island to control rats and mice, prolonged exposure to poisons may have allowed the owls to evolve some tolerance. Milledge (2010) had only limited success trapping owls using drop-nets (Dho-Gaza net). Therefore, trials will be performed prior to the eradication programme to explore the suitability of ‘goshawk-type traps’, which will need to be set after dark and closed prior to dawn to avoid the capture of non-target species such as currawongs. All owls caught during this trial will be destroyed. Timing and personnel Trapping of owls for removal (if shown to be an effective method) will continue from three months before and for up to three months after the REP or longer if necessary until all owls not eliminated by shooting have been removed. Owls will be trapped with goshawk-type traps in two teams of two people. Trapping with goshawk-type traps using live rats as bait will not be possible once the REP commences, as using live rats cannot be risked due to the possibility of their escape. However live trapping may need to be employed as an alternative to shooting post-REP, for example where a particular owl has become too wary to be lured in by call playback or where an owl has been detected in an area of terrain too difficult to allow shooting. In these cases alternative live baits such as guinea pigs or young chickens may be used. Shooting programme The proposed method of removing owls that are not eliminated through secondary poisoning and trapping is through a systematic shooting programme. Because it is inevitable that owls will begin preying on native fauna once rats and mice are removed, it is intended that the shooting programme begins as soon as possible after the REP begins without compromising the trapping programme. Locations across the island will be chosen to provide clear vantage points and suitable overhead perches to enable the shooting of owls. Call playback will be used at these stations to attract owls, at which time they will be shot by experienced, qualified shooters who will be engaged to perform the shooting component. All shooters will be appropriately licensed in accordance with any New South Wales and Lord Howe Island Board requirements. The shooting programme (locations and expected number of owls to be targeted) will be informed by the pre-REP point surveys and acoustic monitoring results. The shooting programme will cover all accessible habitat across the island. However, the first priority should be to target areas that will be difficult for shooters to access on foot. It is proposed that the helicopter(s) used for spreading bait be used to transport shooters to these inaccessible areas either, during the period between the first and second bait drops, or immediately after the second bait drop. It should be noted that the rodent eradication should be prioritised for helicopter use. When being transported to remote areas by helicopter during the day, shooters will carry adequate equipment to enable them to stay overnight as it will be unlikely that they can be picked up that night and inclement weather or other factors may also delay the return of the helicopter. Timing and personnel The shooting schedule will be informed by the population surveys and acoustic monitoring and it is proposed that two teams comprising two persons will perform shooting operations. Shooting in remote areas will begin as soon as is practicable after the first bait drop. The duration and timing of these forays will be dictated by weather and helicopter availability.