Part Summary - National Recovery Plan for the Norfolk Island Scarlet Robin (Petroica multicolor multicolor) and the Norfolk Island Golden Whistler (Pachycephala pectoralis xanthoprocta) - Summary | Zoe
National Recovery Plan for the Norfolk Island Scarlet Robin (Petroica multicolor multicolor) and the Norfolk Island Golden Whistler (Pachycephala pectoralis xanthoprocta)
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Turn the raw legal text into a practical explanation grounded in National Recovery Plan for the Norfolk Island Scarlet Robin (Petroica multicolor multicolor) and the Norfolk Island Golden Whistler (Pachycephala pectoralis xanthoprocta).
The Norfolk Island Scarlet Robin Petroica multicolor multicolor (Robin) and Norfolk Island Golden Whistler Pachycephala pectoralis xanthoprocta (Whistler) are only found on Norfolk Island (29002’S, 167057’E). Although once found throughout the forests of Norfolk Island, and probably also on Phillip Island 6km to the south, each taxon is now restricted to a single population, in Norfolk Island National Park (465ha) and a few forest remnants mainly within 2km of the national park.
The total population sizes are currently estimated to be 440 breeding pairs of Robins and 535 breeding pairs of Whistlers. Total population sizes of both taxa are primarily limited by the small area of remaining suitable habitat, habitat fragmentation, habitat degradation and weed infestation, and introduced predators such as Feral Cats Felis catus and Black Rats Rattus rattus.
This Recovery Plan builds on earlier work to recover the Norfolk Island Green Parrot Cyanoramphus cookii and Norfolk Island Boobook Ninox novaeseelandiae undulata, and incorporates a multi-species approach wherever possible. It outlines actions which should change the conservation status of both the Robin and Whistler from 'Vulnerable' to 'Least Concern' within 20 years. This will be achieved by culling predators in forest remnants near Norfolk Island National Park (NINP), establishing and maintaining forested links to remnants, and if appropriate establishing second breeding populations on Phillip Island, which is free of mammalian predators. Population increases will also be achieved by extending the program to appropriate Public Reserves, providing habitat restoration incentives to private landholders, and involving the community in the recovery program.
Ultimately, the long-term goal should be to make Norfolk Island free of introduced mammalian predators (see Simberloff 2002). While this action is beyond the scope of this Recovery Plan, several studies cited in Veitch and Clout (2002) of Cat and Rat eradication from large islands, including those settled by humans, indicate that total eradication is a feasible target.
Biodiversity Benefits
The actions specified in this Recovery Plan will benefit a range of Norfolk Island threatened species. The existing control of Black Rats and Cats, which was initiated in 1992 mainly for Green Parrot conservation, greatly benefits other island fauna including Robins and Whistlers, a number of threatened plant species, the diverse land mollusk fauna and the two Vulnerable reptile species.
Habitat Critical to Survival
The most extensive area of native habitat remaining on Norfolk Island is within NINP, which encompasses 465 ha - 12% of the main island. Gilmour and Helman (1989) quantified the native vegetation assemblages of the Park at that time as 30% ‘native forest’ (palm, hardwood, and Norfolk Island Pine forest), 37% ‘weed-infested native forest’ and 33% ‘exotic forest’. Robins and Whistlers occur in all habitats within the national park and in some forested areas outside it (Robinson 1988, 1997, Major 1989, Bell 1990). The key elements of habitat critical for the survival of the Robin and Whistler are listed in Attachment 1 (habitat requirements), though the finer details of the Whistler's requirements are poorly known.
Habitat critical for the survival of both species includes all known sites for nesting, food resources, water, and shelter. This includes native and exotic forest and areas inside and outside NINP. Habitat with the potential to support Robins and Whistlers also fit the criteria of habitat critical for survival of the species, and the revegetated areas of Phillip Island may fall into this category, as well as potential habitat on Norfolk Island currently not used by Robins and Whistlers. Further work is needed to define these ‘potential’ areas and confirm their suitability. The known habitat critical for the survival of the Robin and Whistler is mapped in Figure 1 and is defined in this Recovery Plan as all potential Robin and Whistler habitat within their ‘current normal range’. This area is very similar to that determined for the Norfolk Island Green Parrot (Hill 2002). Most of the habitat of the Robin and Whistler is in national park, and public reserves, but some is on private land.
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Threats
Predators
The Black Rat and Feral Cat continue to be the greatest threat to the island’s native vertebrate fauna (Commonwealth 2000). Baiting within the NINP has reduced numbers of the Black Rat (Innes 1995), and this, along with Cat control and the provision of more secure nest sites, has allowed Norfolk Island Green Parrot and Boobook numbers to increase (Olsen 1997, Hill 2002). Black Rats on Norfolk Island are probably the greatest potential risk to breeding seabirds, endemic reptiles, molluscs and any potential translocated birds, on Phillip Island (where there are currently not present).
While the Polynesian Rat Rattus exulans takes birds (McClelland 2002a, Pierce 2002), there has been a long period of co-existence, and it has been suggested that they are not a significant threat to landbirds (ANPWS 1984). Similarly, Norfolk Island Boobooks and Nankeen Kestrels Falco cenchroides may eat small numbers of Robins (Olsen 1997, Robinson 1997), and may take a few Whistlers, but their impact is likely to be small (Robinson 1997). Boobooks have co-existed with Norfolk Island landbirds for millennia, but Kestrels are recently self-introduced.
Habitat Loss, fragmentation and degradation
Native forest within NINP is protected under the EPBC Act, and a range of tree species are protected under Norfolk Island Government legislation. Weed-infestation and loss by natural attrition of mature habitat trees are degrading NINP and consequently, the habitat of Robins and Whistlers. On private land outside the national park, loss of native forest through clearing and by natural causes, and the subsequent expansion of dense weeds which crowd the understorey, is still a significant problem.
Robinson (1997) stated that the primary cause of declines in Robin and Whistler populations outside the NINP was probably past habitat loss and the subsequent fragmentation of the surviving populations into many small and isolated populations (Robinson 1988, Bennett 1990). Accordingly, if populations are to persist outside the park, the issues of habitat restoration and habitat isolation need to be addressed there. Some private landholders have already undertaken initiatives to maintain and extend native habitat for the threatened birds of Norfolk Island.
Vegetation management
Management actions may pose local threats to ground-foraging birds. For example, Robins avoid large bare areas recently cleared of weeds, and these areas may be reinvaded by densely growing weeds making them unsuitable for ground-feeding Robins in particular (Robinson 1997). Removal of grazing may also have a temporary detrimental effect, by reducing the openness of the understorey (Bell 1990). As noted by Mack and Lonsdale (2002), control or even eradication of a single invasive plant species may ultimately produce little benefit, if its demise only sparks the rise of another non-indigenous species.
Information gaps
The level of knowledge of the conservation requirements of the Robin (Robinson 1988, 1997, Major 1989) is sufficient to undertake management actions, such as habitat assessments for translocations, with confidence. On the other hand, there is a paucity of essential information on the Whistler (contra Garnett and Crowley 2000). This lack of detailed biological information will limit the reliability of proposed management actions.
New invasive species
The easiest, cheapest and often only the way to avoid significant impacts of invasives on an island ecosystem, is to prevent them getting to the island. To date, quarantine precautions have focused largely on rodents, but other organisms such as invertebrates, plants and even microorganisms can pose a greater, albeit less obvious, risk (McClelland 2002b).
Disease
Less immediate threats are the introduction of a new disease (Hay 1986), or one-off catastrophic events such as a cyclone (Robinson 1988). Island birds have often evolved in the absence of diseases common in continental bird faunas, and the introduction of such diseases can be disastrous. For example, psittacine circovirus disease was probably responsible for the deaths of many parrots on Norfolk Island in the mid-1970s (Hicks and Greenwood 1990). Similarly, the accidental introduction of avian malaria to Hawaii was probably the main cause of the extinction of several bird species (Hay 1986). Once established, a new disease may persist in feral populations of continental bird species which have resistance. For this reason, McNamara (1989) and Hill (2002) recommended that the eradication of introduced species from islands be given a high priority.
Competition
Competition with introduced birds (Common Blackbird Turdus merula and Song Thrush T. philomelos), and pesticides have been suggested as potential threats (Smithers and Disney 1969; Robinson 1988), although there is little evidence either factor had caused a decline in Robin populations or any other species of songbird (Robinson 1988).