CAN TRAP DATA FROM PREDATOR CONTROL OPERATIONS BE USED TO RELATE STOAT AND SHIP RAT CAPTURE SUCCESS TO MICRO-HABITAT FEATURES?

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1 13th Australasian Vertebrate Pest Conference Proceedings Keven Drew Te Papa Wellington, New Zealand 2-6 May 2005 Hosted by Manaaki Whenua Landcare Research PO Box 69, Lincoln 8152, New Zealand.

2 306 CAN TRAP DATA FROM PREDATOR CONTROL OPERATIONS BE USED TO RELATE STOAT AND SHIP RAT CAPTURE SUCCESS TO MICRO-HABITAT FEATURES? Jenny Christie 1, Josh Kemp 1, Chris Rickard 2 and Elaine Murphy 1. 1 Research, Development & Improvement, Department of Conservation, P.O. Box 13049, Christchurch, New Zealand (jchristie@doc.govt.nz) 2 Department of Conservation, P.O. Box 14, Franz Josef ABSTRACT: Stoats (Mustela erminea) and ship rats (Rattus rattus) are major pests threatening New Zealand s native fauna. Control of these pests is being undertaken at sites throughout New Zealand to improve the breeding success and survival of threatened wildlife (Elliot 1996; Moorhouse et al. 2003; Gillies et al. 2003). Knowledge of the habitat factors that influence capture success is essential for improving pest control strategies. We were interested to see if trapping data, which is collected on a large scale and at relatively low cost, could be used in exploratory data analysis to look for micro-habitat features which may improve the probability of stoat and rat capture success. Generalised linear models were used to explore the relationship between a suite of microhabitat features and whether a predator was killed in a trap. We used data collected from large scale predator control operations at Okarito and Moehau kiwi (Apteryx spp) sanctuaries (Fig. 1). Direct comparison of models between the sanctuaries was not possible because micro-habitat features were recorded independently and in a different way at each sanctuary

3 307 A number of micro-habitat features significantly influenced the probability of catching both stoats and rats (Table 1). Many of the model results are consistent with findings from other research. For example, rat capture success increased in mature hardwood podocarp forest types at both sanctuaries and in subalpine scrub and scrub grassland mosaics at Moehau only. Habitat margins, such as road and lake margins, either had no effect or decreased the probability of catching a rat. Similar results for ship rats have been documented both in New Zealand and overseas (e.g., Dowding and Murphy, 1994; King et al., 1996; White et al., 1997; Cox et al., 2000) Fig. 1. Location of study areas.

4 308 Table 1. The best fit multiple logistic regression models of the probability of stoat or rat capture at Okarito and Moehau Kiwi Sanctuaries as predicted by micro-habitat features. Micro-habitat features are recorded for the area immediately surrounding the trap site unless a radius is specified (Note: n.i. = not included in final model; + n.s. = positive effect, not significant; - n.s. = negative effect, not significant; + = positive effect, significant at the 5 % level; ++ = positive effect, significant at the 1 % level; +++ = positive effect, significant at the 0.1 % level; - = negative effect, significant at the 5 % level; -- = negative effect, significant at the 1 % level; --- = negative effect, significant at the 0.1 % level). Examples of model interpretation are: the probability of stoat capture success increased 1 with the presence of a road edge and 2 as the soil around the trap became less moist at Okarito. Location Micro-habitat feature Stoat model Rat model Okarito Presence of rat plague ni +++ Trapping edge (buffer/core) ni --- Altitude (metres a.s.l.) - ns Presence of road edge Presence of track edge +++ ni Presence of farm edge ++ + Presence of undulating topography within 50 m ni --- Presence of flat topography within 50 m Presence of ridge within 50 m +++ ni Presence of tall podocarp forest within 100 m ni +++ Presence of short sub canopy forest within 100 m ni + ns Presence of forest with thick & abundant kiekie within 100 m ni +++ Presence of pakihi/swamp within 100 m + ni 2 Soil drainage Understorey density within 15m - ns ni Moehau Altitude (metres a.s.l.) ni --- Presence of major stream - ni Presence of major ridge + -- Presence of old hardwood/broadleaf forest Presence of sub alpine scrub + + ns Presence of a grassland/manuka habitat mosaic Presence of manuka/kanuka scrub + + Presence of a rough dirt vehicle track + ns --- Presence of a car road ni - ns Model results were confounded by the trap layout. Trap location was determined by ease of access and other logistical constraints. For example, the probability of catching a stoat increased at Okarito when a road, track or farm margin was present and at Moehau with the presence of a rough dirt vehicle track. However, not all bush margins had the same positive effect, some had no effect and others such as the presence of a major stream margin at Moehau significantly decreased the probability of stoat capture. Traps along road margins were checked more frequently, and therefore were available to catch more animals. Moreover, road and farm edges denote the trapping boundaries at both sanctuaries. These traps would catch more stoats precisely because it is the trapping boundary and there are more stoats to catch, not because of any particular habitat features.

5 309 Further investigation into the relationship between micro-habitat features and capture success is required, but needs to utilise random / systematic study design. This will aid in easier model interpretation and ensure stronger inference can be made from the model findings; disentangling the effects of trapping edge and biased topographical layout from trap capture success; and allow investigation into model interaction effects. Trap data from predator control operations should not be used for habitat analyses unless the sampling design is robust. Findings from our model will be used to select the types of micro-habitat features recorded in future research. These micro-habitat features should be standardised nationally, reflect biological mechanisms, be recorded as a continuous measure where possible and nest small scale spatial variables within large scale spatial variables. REFERENCES Cox, M.P.G.; Dickman, C.R.; Cox, W.G Use of habitat by the black rat (Rattus rattus) at North Head, New South Wales: an observational and experimental study. Austral Ecology 25: Dowding, J.E.; Murphy, E.C Ecology of ship rats (Rattus rattus) in a kauri (Agathis australis) forest in Northland, New Zealand. New Zealand Journal of Ecology 18: Elliott, G.P Productivity and mortality of mohua (Mohoua ochrocephala). New Zealand Journal of Zoology 23: Gillies, C.A.; Leach, M.R.; Coad, N.B.; Theobald, S.W.; Campbell, J.; Herbert, T.; Graham, P.J.; Pierce, R.J Six years of intensive pest mammal control at Trounson Kauri Park, a Department of Conservation "mainland island", June 1996-July New Zealand Journal of Zoology 30: King, C.M.; Innes, J.G.; Flux, M.; Kimberley, M.O.; Leathwick, J.R.; Williams, D.S Distribution and abundance of small mammals in relation to habitat in Pureora Forest Park. New Zealand Journal of Ecology 20: Moorhouse, R.; Greene, T.; Dilks, P.; Powlesland, R.; Moran, L.; Taylor, G.; Jones, A.; Knegtmans, J.; Wills, D.; Pryde, M.; Fraser, I.; August, A.; August, C Control of introduced mammalian predators improves kaka Nestor meridionalis breeding success: Reversing the decline of a threatened New Zealand parrot. Biological Conservation 110: White, J.; Wilson, J.; Horskins, K The role of adjacent habitats in rodent damage levels in Australian macadamia orchard systems. Crop Protection 16: