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Friend or foe? The controversial status of native predators in New Zealand restoration projects using weka as a case study species – Asher Cook

Introduced predators have had a catastrophic impact on New Zealand’s unique flora and fauna (King, 1984; O’Donnell, 1996; Holdaway, 1999).  Generally, given their non-native status, the control or eradication of introduced predators is a logical procedure that results in clear conservation benefits for native biodiversity (Moorhouse et al. 2003; Whitehead et al. 2008).  However, an important but often overlooked issue arises when predation pressure is exerted by native species.  In this case, the distinction between predator control and conservation gain is blurred and is exacerbated when the predator is, itself, a threatened species.  This paradoxical situation raises an important question – are New Zealand’s native predators friend or foe?  This essay will (1) focus on weka (Gallirallus australis) as a real-life example of a native New Zealand predator, (2) present the arguments for and against their inclusion in restoration projects and (3) provide a generalised decision-making framework designed to help conservation practitioners who are considering the reintroduction of a native predator species.

New Zealand’s native predators

New Zealand has a number of native species that are at least part-time predators of native vertebrate fauna – avian examples include swamp harrier, pukeko, morepork, New Zealand Falcon and weka (van Winkel & Ji, 2012; Dey & Jamieson, 2013). They consume a wide range of prey including birds, lizards and bats, and several of these predator species have been controlled to protect rare native species (Seaton & Hyde, 2013). Both weka and New Zealand falcon are threatened with extinction (Miskelly et al. 2008).

Why can native predators pose problems in New Zealand? 

Generally in natural predator-prey scenarios the prey species are robust enough to withstand predation from native predators (Salo et al. 2007).  Yet, many of New Zealand’s surviving endemic species have small and fragmented populations in which even relatively low rates of predation by native species may cause population decline (especially when coupled with predation by introduced species).  This means that in some scenarios native predators pose a significant threat to native biodiversity.  Pukeko, for example, are controlled in pateke/brown teal breeding areas due to the threat they pose at high densities to eggs and ducklings (O’Connor et al. 2007; Dey & Jamieson, 2013).

Weka

Figure 1.  Adult North Island weka (retrieved on 5/04/14 from http://nzbirdsonline.org.nz/species/weka)

Figure 1. Adult North Island weka (retrieved on 5/04/14 from http://nzbirdsonline.org.nz/species/weka)

The weka is an iconic large flightless endemic rail (figure 1).  Originally found throughout mainland New Zealand, they are now extinct over large tracts of their former range due to a combination of predation (particularly by mustelids), drought susceptibility and habitat loss (Beauchamp, 1997; Miskelly & Beauchamp, 2004).  Three of the four subspecies are listed as threatened according to the New Zealand Threat Classification System (Molloy et al. 2002) with the northern and Stewart Island weka listed as ‘nationally vulnerable’ and the western weka as ‘declining’ (Miskelly, 2008).  Though invertebrates and fruit constitute most of their diet they also opportunistically prey on lizards, snails, eggs and juvenile ground nesting birds (Harper, 2006).

Weka have the potential for both negative and positive spin-offs for native biodiversity.  Therefore they provide an important case study to compare the advantages and disadvantages of including a native predator in a restoration project.

Is it friend…?

There are a number of reasons that support the inclusion of weka within restoration projects. Conservation benefits include increased dispersal of large-fruited plants such as hinau, tawa and taraire (Beauchamp& Butler, 1999).  This is especially important because most other species capable of dispersing large seed are now either extinct or absent across large areas of the country (Clout, 1989).  In addition, weka also prey upon mammalian pests (namely rats and mice) so can provide a natural form of pest control within mainland sanctuaries –  this is particularly significant in unfenced sites where total eradication of introduced mammals is currently infeasible (Saunders & Norton, 2001).

Most of the high-impact weka scenarios have occurred on seabird-dominated offshore islands more than 1 km from the mainland where weka do not naturally occur (Miskelly & Beauchamp, 2004).  The grounds for eradication from off-shore islands (where weka often reach high densities) should not necessarily be applied to mainland sanctuaries which are generally within their natural range.  In ‘natural’ mainland populations it is likely that other native vertebrate species could cope with weka predation (unless prey populations are particularly small or vulnerable) (Salo et al. 2007).  Weka also hold strong cultural significance to some iwi and their availability for sustainable harvest remains an important issue (Beauchamp & Butler,1999).

Weka are prone to rapid population decline and as a result they are now more threatened than many of the species that restoration projects are designed to protect (Miskelly, 2008). North island weka populations in the Gisborne region plummeted during the mid-1980s through to the early 1990s and disappeared from a majority of their former range (Beauchamp et al. 1998).  Similar sharp declines were also observed in a Northland population over a similar period when the local population declined from approximately 400 birds to just three individuals in only eight years (Beauchamp, 1997).  Many of the large, stable weka populations now occur on offshore islands (Chathams, Kawau, Kapiti) where they have been introduced and act as an important insurance policy to their fragile mainland counterparts.

Their threatened status and susceptibility to sudden population decline suggests that at least limited inclusion in restoration projects is essential to their long-term survival.

Or is it foe…?              

Figure 2.  Red dots represent approximate location of islands where weka had been eradicated pre-2004 (adapted from Miskelly & Beauchamp, 2004). Map was retrieved on 6/04/14 from GoogleEarth.

Figure 2. Red dots represent approximate location of islands where weka had been eradicated pre-2004 (adapted from Miskelly & Beauchamp, 2004). Map was retrieved on 6/04/14 from GoogleEarth.

Arguments against their inclusion in restoration projects focus mainly on the negative impact they can have on other native vertebrates.  Weka have a documented history of predation on a wide range of native species.  These include sooty shearwater chicks on the southern Titi Islands (Harper, 2006), petrels on Macquarie Island (Brothers, 1984), lizards on islands free of introduced mammals (Hitchmough, 1998), saddleback (Lovegrove, 1992; Roberts, 1994), North Island kaka, little spotted kiwi (Miskelly & Beauchamp, 2004), snipe (Miskelly, 1987) and Fiordland-crested penguins (St. Clair & St. Clair, 1992).  Furthermore, they are thought to have contributed to the extinction of the Macquarie island parakeet (Taylor, 1979).  As a result, weka have been removed from at least nine island restoration projects (figure 2) and have been excluded from the reintroduction lists of many mainland projects (Miskelly & Beauchamp, 2004).  However, in most examples it remains unclear whether weka predation rates are high enough to induce population decline.  Further quantitative research is needed to more accurately determine their impact and would bring more scientific rigour to the ongoing debate.

Their potential for negative impacts on such a wide range of native species suggests that ubiquitous inclusion in restoration projects is neither logical nor feasible.

Posing the important questions

There are a number of important questions that conservation practitioners face when considering their stance on weka – these questions can be applied to other similar situations involving native predator species.  The first clear distinction to consider is whether the predator species is already present within the boundaries of the restoration project.  Logically, if it is already present then decision making will focus on whether or not to remove the predator.   Conversely, if it is absent, focus will be placed on the whether to undertake a reintroduction.

Listed below (figure 3) are some important questions to contemplate when considering the reintroduction of a native predator[1]:

Figure 3. Generalised decision-making framework designed to help conservation practitioners who are considering the reintroduction of a native predator species.

Figure 3. Generalised decision-making framework designed to help conservation practitioners who are considering the reintroduction of a native predator species.

In the case of question (1) if the extinction threat (refer to Miskelly, 2008) of the potential prey species are higher than the extinction threat of the predator, a reintroduction effort should not be considered given that even low rates of additive predation can exert severe population pressure on small populations (O’Donnell, 1996).  In this situation other reintroduction sites with less threatened prey species should be considered.

In cases where the extinction threat of the prey species is low but concern remains over the impact of the reintroduced predator, population modelling (incorporating the expected predation rate) can give some idea of the likely scale of impact.  In this case, question (2) should be considered because empirical site-specific population data is required for accurate modelling and informative predictions.

Before practitioners proceed with a reintroduction, questions (3) and (4) should also be considered.  Evidence of coexistence in similar situations provides strong evidence that a reintroduction could be successful for both predator and prey.  In circumstances where there are no examples of coexistence then reintroduction efforts should be considered with extreme caution.  Question (4) is also an inquiry of fundamental importance given that predator impacts are usually intensified outside of their natural range (Salo et al. 2007).  As mentioned earlier, most high-impact weka scenarios have occurred on offshore islands outside of their natural range (Miskelly & Beauchamp, 2004).

Conclusion

It is well-documented that introduced mammalian predators have had a detrimental impact on New Zealand’s biodiversity (Holdaway, 1999; Croll, 2005).  Therefore, the control of predators is generally a logical procedure that leads to clear benefits for native biodiversity.  However, when predation pressure is exerted by native species the distinction between predator control and conservation gain is made unclear.  In this scenario there is no easy answer.

Sometimes native predators are our friends.  Sometimes they are foe.

The example of weka in New Zealand emphasises the need for flexibility in our approach toward native predators in restoration projects.

 

 

 

References

Beauchamp, A. J. & Butler, D.J. (1999).  Weka (Gallirallus australis) recovery plan.

Beauchamp, A. J. (1997). The decline of the North Island weka (Gallirallus australis greyi) in the East Cape and Opotiki Regions, North Island, New Zealand. Notornis, 44, 27-36.

Beauchamp, A. J., Van Berkum, B., & Closs, M. J. (1998). The decline of North Island Weka (Gallirallus australis greyi) at Parekura Bay, Bay of Islands. Notornis, 45, 31-43.

Brothers, N. P. (1984). Breeding, Distribution and Status of Barrow-nesting Petrels at Macqaurie Island. Wildlife Research, 11(1), 113-131.

Clout, M. N., & Hay, J. R. (1989). The importance of birds as browsers, pollinators and seed dispersers in New Zealand forests. New Zealand journal of ecology, 12(Supplement), 27-33.

Croll, D. A., Maron, J. L., Estes, J. A., Danner, E. M., & Byrd, G. V. (2005). Introduced predators transform subarctic islands from grassland to tundra. Science, 307(5717), 1959-1961.

Dey, C.; Jamieson, I. 2013. Pukeko. In Miskelly, C.M. (ed.) New Zealand Birds Online. www.nzbirdsonline.org.nz

Harper, G. (2006). Weka (Gallirallus australis) depredation of sooty shearwater/titi (Puffinus griseus) chicks. Notornis, 53(3), 318.

Helber, L. E. (1995). Redeveloping mature resorts for new markets. In M. V. Conlin & T. Baum (Eds.), Island tourism: Management principles and practice (pp. 105-113). Chichester, England: John Wiley

Hitchmough, R. A., Tutt, K., & Daugherty, C. H. (1998). Significance of gecko populations on islands in Lakes Wanaka and Hawea. Department of Conservation.

Holdaway, R. N. (1999). Introduced predators and avifaunal extinction in New Zealand. In Extinctions in near time (pp. 189-238). Springer US.

King, C. M. (1984). Immigrant killers: introduced predators and the conservation of birds in New Zealand (p. 224). Auckland: Oxford University Press.

Lovegrove, T. G. (1992). The effects of introduced predators on the saddleback (Philesturnus carunculatus), and implications for management (Doctoral dissertation, ResearchSpace@ Auckland).

Miskelly, C. & Bauchamp, A.J. (2004). Weka, a conservation dilemma. In Brown, K. (Ed.), Restoring Kapiti – Nature’s Second Chance (pp. 81 – 86). Dunedin, New Zealand: University of Otago Press.

Miskelly, C. M. (1987). The identity of the hakawai. Notornis, 34(2), 95-116.

Miskelly, C. M., Dowding, J. E., Elliott, G. P., Hitchmough, R. A., Powlesland, R. G., Robertson, H. A.,& Taylor, G. A. (2008). Conservation status of New Zealand birds, 2008. Notornis, 55(3), 117-135.

Molloy, J. (2002). Classifying species according to threat of extinction: a system for New Zealand (No. 22). Biodiversity Recovery Unit, Dept. of Conservation.

Moorhouse, R., Greene, T., Dilks, P., Powlesland, R., Moran, L., Taylor, G., … & August, C. (2003).  Control of introduced mammalian predators improves kaka (Nestor meridionalis) breeding success: reversing the decline of a threatened New Zealand parrot. Biological Conservation, 110(1), 33-44.

O’Donnell, C. F. (1996). Predators and the decline of New Zealand forest birds: an introduction to the hole‐nesting bird and predator programme.

Roberts, A. (1991). A recovery plan for the South Island saddleback. Report to Southland Conservancy, Department of Conservation, New Zealand.

Salo, P., Korpimäki, E., Banks, P. B., Nordström, M., & Dickman, C. R. (2007). Alien predators are more dangerous than native predators to prey populations. Proceedings of the Royal Society B: Biological Sciences, 274(1615), 1237-1243.

Saunders, A., & Norton, D. A. (2001). Ecological restoration at mainland islands in New Zealand. Biological Conservation, 99(1), 109-119.

Seaton, R.; Hyde, N. 2013. New Zealand falcon. In Miskelly, C.M. (ed.) New Zealand Birds Online. www.nzbirdsonline.org.nz

Seaton, R.; Hyde, N. 2013. Morepork. In Miskelly, C.M. (ed.) New Zealand Birds Online. www.nzbirdsonline.org.nz

St Clair, C. C., & St Clair, R. C. (1992). Weka predation on eggs and chicks of Fiordland crested penguins. Notornis, 39, 60-63.

Stephens, P. A., & Sutherland, W. J. (1999). Consequences of the Allee effect for behaviour, ecology and conservation. Trends in Ecology & Evolution, 14(10), 401-405.

Taylor, R. H. (1979). How the Macquarie Island parakeet became extinct. New Zealand Journal of Ecology, 2, 42-45.

Turbott, E. G. (1990). Checklist of the birds of New Zealand. Wellington, Ornithological Society. p 247

O’Connor, S. M., Maloney, R., & Pierce, R. J. (2007). Pateke (Anas chlorotis) recovery plan, 2005-10. Science & Technical Pub., Department of Conservation.

van Winkel, D., & Ji, W. (2012). Evidence of lizard predation by New Zealand kingfishers (Todiramphus sanctus vagans) and potential implications for threatened species translocations. New Zealand Journal of Zoology, 39(3), 201-208.

Whitehead, A. L., Edge, K. A., Smart, A. F., Hill, G. S., & Willans, M. J. (2008). Large scale predator control improves the productivity of a rare New Zealand riverine duck. Biological conservation, 141(11), 2784-2794.

 

 

 

 

 

[1] This list of questions should be used in conjunction with those asked in regular reintroductions.  See Seddon et al. 2007 (http://onlinelibrary.wiley.com/doi/10.1111/j.1523-1739.2006.00627.x/full) and Armstrong et al. 2008 (http://ac.els-cdn.com/S0169534707003345/1-s2.0-S0169534707003345-main.pdf?_tid=7ee08b5c-bc6c-11e3-a7b0-00000aab0f27&acdnat=1396666172_79fb8b9cdd14260d86ca36bb2f595a7f)  for more background information.

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