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The Weta 43: 33-47 33

Use of rock crevices as refuges by the tree weta Hemideina femorata Hutton 1897 (Orthoptera: Anostostomatidae) at Mt Cass, Canterbury

Matthew B. Scott1, Warren Chinn2, Mary Morgan-Richards3 1Institute of Eastern-Himalaya Biodiversity Research, Dali University, Dali, Yunnan, China 671003 2Department of Conservation, Christchurch, New Zealand 3Institute of Natural Resources, Massey University, Private Bag 11-222, Palmerston North 4442, New Zealand

Corresponding author: Matthew B. Scott, Institute of Eastern-Himalaya Biodiversity Research, Dali University, Dali, Yunnan, China 671003 Email: [email protected]

Abstract The Canterbury tree weta, Hemideina femorata, is reported from coastal Mt Cass, Canterbury where it was observed in narrow rock crevices and under large limestone slabs in escarpment, pavement and boulder over 480 m above sea level (a.s.l.). No tree weta were observed occupying logs, tree cavities, under bark, or leaf foliage, suggesting that this population might have a local preference for rock refuges over tree holes. Five of seven rock galleries observed were cohabitated by Canterbury ( aff. brunnea). Our observations on Mt Cass were of a tree weta population at low density. The restriction of weta to the ridgeline, and seemingly ample unused available may be symptomatic of a diminished population or one at the limits of its natural range.

Keywords Hemideina femorata, habitat use, distribution, limestone habitat

Introduction The Canterbury tree weta, Hemideina femorata Hutton 1897 is a large (c. 40–60mm), flightless orthopteran distributed on the eastern side of the Southern Alps, from Kaikoura to southern Canterbury, including Banks 34 Matthew Scott, Warren Chinn and Mary Morgan-Richards

Peninsula (Field & Bigelow, 2001; Meads, 1990; Townsend et al., 1997; Gibbs, 1998a; Gibbs, 2001). Like all tree weta, H. femorata are nocturnal, remaining in protective refuges during the day and emerging at night to feed. Hemideina femorata are typically found in forest and shrubland habitats below 500 m a.s.l. (above sea level), sheltering in small galleries in living tree cavities, under bark, and occasionally in or under logs (Townsend et al., 1997). On , kanuka (Kunzea ericoides) is the most commonly selected refuge host, but H. femorata have also been found using narrow-leaved lacebark (Hoheria angustifolia), pate (Schefflera digitata), mahoe (Melicytus ramiflorus), and the vines of bindweed (Calystegia sp.) (Townsend et al.. 1997). Elsewhere in Canterbury, H. femorata have been reported in a wider range of , including beech (Nothofagus sp.), Fuchsia excorticata, and broadleaf (Griselinia littoralis) (Little, 1980; Field & Sandlant, 2001). Tree weta practice a type of resource defence polygyny in which males aggressively compete for galleries where females aggregate (Sandlant, 1981; Field & Jarman, 2001; Kelly, 2006). Dominant males vigorously defend for rights of harems (typically one to three females; Field & Jarman, 2001).

Hemideina femorata was first discovered on Mt Cass on 21 December 2007 (W. Chinn, pers. obs. 2007). This first observation was of a single female beneath a large horizontal limestone slab. Two subsequent observations were made on 24 October and 11 November 2008 during a herpetofauna survey (M. Lettink, pers. comm. 2008). The first of these observations was of a single adult male under a horizontal limestone slab. The second of these observations was of a pair (adult male and adult female) in the crevice of a fractured limestone block. All three observations were made near to or on the main ridgeline in seral grey shrubland habitat bordering forest or dense scrub vegetation and open pasture.

In 2009, as part of the application process to construct and operate a power generating windfarm on the Mt Cass ridge, Main Power Limited commissioned a more detailed survey of the distribution and habitat-use of H. femorata on Mt Cass. The results of that survey, as well as known previous and subsequent observations are given here. Weta are flagships for invertebrate conservation in New Zealand, and part of strategic conservation management and ecological monitoring (Gibbs, 1998b; The Weta 43: 33-47 35

Trewick & Morgan-Richards, 2000; Sherley, 2001; Lee et al., 2005). New and unusual records provide important resolution to the current and historical geographic distribution, as well as habitat preferences of the species. Methods Site Description Mt Cass ridge (557 m a.s.l.) is situated just east of Waipara, in the Motunau Ecological District, Canterbury (43.078S, 172.824E). The underlying geology is tertiary limestone including Amuri and Weka Pass limestone. The linear ridgeline forms a syncline along a northeast–southwest axis. The uppermost part of the north-western face has a short (<40 m) steep scarp punctuated by numerous rocky outcrops, colluvial boulders, and sparse patches of shallow scree material. The broad and comparatively gentler south-facing dipslope is characterised by a complex pattern of elevated eroded limestone pavements on prominent sub-ridges. Sub-ridges are interspersed by dry, generally rock-less gullies, often with prominent dolines. The limestone (predominantly Weka Pass) pavement includes extensive clint and gryke geomorphology, flutings (rundkarren), solution cups, perched soil patches and bedrock overhangs. Most rock features are partially buried in the soil; however, shattered slabs, loose boulders and fissures are relatively common in the soft limestone providing a range of crevices and under-rock micro-habitats for invertebrates and other fauna. The current vegetation is a mosaic of broadleaved–podocarp forest, broadleaved scrub, grey shrubland, tussock grassland and pasture (Fig. 1A– C). Although widespread, the native woody vegetation is predominantly along the ridge crest, on south-eastern sub-ridges, and down the eastern dipslope, including some of the lower gullies. Forest and scrub canopy composition is predominantly broadleaf (Griselinia littoralis) five-finger (Pseudopanax arboreus), mahoe (Melicytus ramiflorus), and lemonwood (Pittosporum eugenioides). Narrow-leaved hoheria (Hoheria angustifolia) and kowhai (Sophora microphylla) are also common, particularly along forest edges and comprising early-stage forests. Ribbonwood (Plagianthus regius) is primarily in the forested mid- and lower-slope gullies . Numerous remnant totara (Podocarpus totara) and matai (Prumnopitys taxifolia) are present; old-growth kahikatea () is rare. Remnant hardwoods are primarily G. littoralis. The forest canopy is generally very low (<5 m along the ridge, <10 m upper slopes), though 36 Matthew Scott, Warren Chinn and Mary Morgan-Richards some remnant podocarps on the dip slope exceed 20 m. Open grey shrubland consists of a scattering of shrubs (predominantly propinqua and Raukaua anomalus). Shrubland understory is dominated by silver tussock (Poa cita) and adventive pasture species. Forest cover on the northern slope has been largely removed, with only a few smaller patches of forest and grey shrubland, usually fortified from livestock by cliffs, boulder clusters or steep-sided dolines. Below the limestone– mudstone interface at c. 400 m a.s.l. on the northern face, an abrupt vegetation shift occurs where matagouri (Discaria toumatou) shrubland and kanuka (Kunzea ericoides) scrub are the dominant seral native communities.

The original vegetation is likely to have been predominantly broadleaved– podocarp forests on the slopes with dwarfed forest and scrub vegetation along the summit ridge crest (Molloy et al., 1963); burned and stunted P. totara logs and stumps along the summit ridge give some evidence of this (M. Scott, pers. obs. 2009). The vegetation was initially modified by Polynesian burning, and subsequently partially cleared and grazed for pastoral farming, (Molloy et al., 1963; McGlone, 1983; Ogden et al., 1998). From at least the 1950’s, woody vegetation has increased in extent and canopy density, particularly around the rocky features along the main ridgeline (Golder Associates 2008).

Mt Cass has retained a distinct assemblage of plant species and is a regional hotspot for native plant biodiversity, including several calcicole species; descriptions of the vegetation and flora can be found at Molloy (1994), Stephen (2000), and Golder Associates (2008). The Weta 43: 33-47 37

Survey Hand searches were carried out along the Mt Cass Ridge on 17 and 18 March 2009 in daylight by inspecting all rock crevices, rock piles, tree cavities, logs, and hanging cabbage tree () foliage encountered across a range of habitats. Searching specifically for weta was undertaken in all habitats, from open grass through a series of ecotones into forest interior. Searches were done with the aid of a Silva (25 watt halogen) head torch. When possible, rock and woody material was lifted and returned to its original place. Habitat, microhabitat, altitude and direction of slope (aspect) of each locality were recorded.

Weta identification Tree weta species identification used three characters considered diagnostic when used in combination. Stridulatory ridge counts can separate the five species of Hemideina into three groups. Hemideina maori (Picket & Saussure 1891) and H. ricta Hutton 1897 usually have more than 19 stridulatory ridges (right + left), while H. femorata and H. crassidens (Blanchard 1851) have fewer than 16 (Fig 2A; Morgan-Richards & Townsend, 1995; Field & Bigelow, 2001), and H. broughi (Buller 1896) has no stridulatory ridges. Hemideina crassidens, H. ricta and H. broughi have dark pronotums and H. femorata and H. maori have pale pronotums with prominent markings (Fig 2B; Field & Bigelow, 2001). The shape of the mandibles of these species differs; although all except H. broughi have elongated mandibles in adult males (compared to females), only H. femorata has a characteristic carina as shown in Fig. 2C.

Results In two days, or approximately 12 h of concentrated searching, two H. femorata were observed (Table 1; Fig. 3). The weta (one male and one female) were found together in a narrow (<2 cm) cavity under a large (c. 50 cm diameter) limestone (Weka Pass Limestone) slab. The rock was resting on a solid limestone outcrop. The cavity was also occupied by 15 Canterbury (Woodworthia aff. brunnea). Subsequent to the weta survey, three more observations were made during flora and fauna surveys (Table 1). The first specimen was a dead female. It was found on 18 March 2009 on a horizontal ledge at the mouth of a small (<2 cm) fissure, beneath a large (c. 2 m diameter) overhanging boulder resting on bedrock. The boulder was part of a larger area of 38 Matthew Scott, Warren Chinn and Mary Morgan-Richards boulders on a northeast facing slope. The body did not show signs of . The second specimen observed was also female. It was found on 20 March 2009 under a broad rock slab on a raised limestone pavement. The cavity (c. 3 cm) was also occupied by a single sub-adult Canterbury gecko. Another pair (one male, one female) was found on 24 January 2012 in a fractured boulder on a north-facing forest margin (A. Hurley, pers. comm. 2012) (Fig. 1D.). The crevice was sub-horizontal, approximately 1 m above ground, and also occupied by several Canterbury gecko.

All weta observed on Mt Cass to date have been in dry, narrow (<3 cm) rock cavities, with rock rather than soil substrate. Rock refuges tended to be adjacent to woody vegetation (dominated by , Raukaua anomolus, and stunted Griselinia littoralis), or on the edge of broadleaved forest. Ground cover in the vicinity of weta refuges was mainly dominated by silver tussock (Poa cita) and adventive pasture species, though none of the seven recorded weta refuges were in rock features set in open grassland habitats. No evidence of H. femorata has yet been found in forested habitats, tree or log cavities, or on cabbage trees. Previous day- and night-time hand surveys of logs and leaf litter in forest interiors also failed to detect H. femorata (M. Scott, pers. obs. 2007). No observations of H. femorata have yet to be made below 480 m a.s.l. on Mt Cass. Discussion This new record of Hemideina femorata on the coastal limestone Mt Cass ridge is well within the current known range of Hemideina femorata, but is near the currently recorded altitudinal limit for this species. On Banks Peninsula, H. femorata has been found as high as 440 m a.s.l., but more typically found below 320 m a.s.l. (Townsend et al., 1997). Further north near Hanmer Springs, H. femorata has been collected from beech and kanuka forest between 500 and 610 m a.s.l. (Little, 1980). Hemideina femorata were only found in rock crevices and under large limestone slabs on Mt Cass. Previous records from elsewhere in its range show H. femorata more typically use holes and cavities in trees and bark for refuge (Field & Sandlant, 2001); there are, as far as we are aware, no other records of H. femorata using rock cavities. Until now we considered H. maori to be the only Hemideina species to regularly use such ground level, rock crevice habitat, though its sister species, H. ricta, was found The Weta 43: 33-47 39 under rocks and in crevices between rocks at four sites on the Banks Peninsula in situations where there is was shortage of suitable woody refuges (Townsend et al., 1997).

It is possible that rock cavity use by tree weta is more widespread than previously assumed, because biologists looking for tree weta (with the principal exception of those searching for H. maori) tend to concentrate their searches in forest and scrub habitat where cavities in tree branches are the focus of search effort. For example, H. crassidens is found at the tree line on Mt Taranaki 1,200 m a.s.l. (Trewick & Morgan-Richards, 1995), but there have been neither searches nor records of H. crassidens above the tree line due to an absence of what was previously regarded as essential habitat (e.g., trees). Three lowland tree weta species (H. thoracica, H. crassidens, H. ricta) can all survive freezing in much the same way that the alpine species H. maori can (Sinclair et al. 1999). Thus, it is likely that H. femorata is also freeze tolerant. Given the large-scale changes of the Pleiostocene it is possible many of New Zealand’s seven Hemideina species have survived in situ without extensive lowland forest cover and are tolerant of a wide range of conditions.

While the present study provides evidence of H. femorata using rock cavities on Mt Cass, we cannot exclude the likely scenario that H. femorata are also using tree cavities within the forest on Mt Cass. Observer discovery rate was influenced by two important contributing factors. First, living tree-holes and rock fissures were not opened, whereas logs and rock slabs were lifted. Thus, results of searches of rock fissures and tree holes should be regarded as an underestimate relative to rock slabs and logs. Moreover, three of the weta records also were the result of lizard surveys when observers were specifically targeting rocky micro-habitats, so all rocky habitats have been preferentially searched. Second, rock cavities may simply be more efficient to examine. Rock slabs and crevices were abundantly distributed, easily spotted, and easily checked in a short period of time. Whereas, trees with cavities and cabbage tree foliage were generally spread more widely, suitable holes were often quite cryptic, and often awkward to inspect (e.g., required climbing the tree or manoeuvring in dense vegetation). These characters are likely to have greatly decreased the sample rate of these microhabitats, and decreased the chance of discovery in an occupied tree hole or cabbage tree. Success rate for finding 40 Matthew Scott, Warren Chinn and Mary Morgan-Richards tree weta is dependent on site, habitat and species. In Kaikoura kanuka forest, 62% of tree holes contained H. femorata and in Westland broadleaf forest 41.6% of tree holes contained H crassidens (Field & Sandlant, 2001), whereas only 3% of examined suitable holes on Banks Peninsula were occupied by weta (Townsend et al., 1997), suggesting that the current study could easily have missed weta in woody cavities. Griselinia littoralis was the most common tree in the forest habitat and is known to provide suitable refuge holes for H. femorata elsewhere (Little, 1980; Sandlant, 1981). However, our searching method did not open cavities in living trees, thus, only high densities of H. femorata in the forest would have allowed easy detection.

The adult Mt Cass tree-weta population, although at low density, was only found on the ridgeline. Given the concentrated search effort, as well as numerous other plant, lizard and invertebrate surveys completed in the area (M. Lettink and T. Bell, pers. com. 2010), remarkably few weta have been recorded. However, potential wood and rock refuges are seemingly plentiful. If the abundance of Canterbury gecko retreats is used as a crude indicator for potential rock microhabitat (Bell & Herbert, 2010), it could be assumed numerous uninhabited rock refuge sites exist within the current distribution. A large suite of introduced mammalian predators exist at the site: (Felis catus), (Mustela fero), (Mustela erminea), (Erinaceus europaeus), (Rattus spp.) and mice (Mus musculus) (Excell Biosecurity, 2009; M. Scott, pers. obs. 2007–2010). All these species prey on weta (Gibbs, 1998b; 2001), and may, at least in part, contribute to the distribution pattern and density of tree weta on Mt Cass.

Acknowledgements Marieke Lettink and Trent Bell are thanked for their detailed observations and thoughtful comments. Thanks also to Andrew Hurley who collected and posted two tree weta vouchers. Landowners, MainPower New Zealand Limited and Robin Gardiner are kindly thanked for land access. MainPower Ltd funded field surveys and provided aerial photography. References Bell T, Herbert S 2010 Canterbury gecko ( sp. 'Canterbury') occupancy and habitat studies at the proposed Mt Cass wind farm. Unpublished report to MainPower New Zealand Limited, Rangiora. The Weta 43: 33-47 41

Excell Biosecurity 2009 2009 Vermin Survey–Mt Cass Windfarm. Unpublished report to MainPower New Zealand Limited, Rangiora.

Field LH, Jarman TH 2001 Mating Behaviour. In: The Biology of Wetas, King Crickets and their Allies (ed LH Field) pp. 317–332. CABI Publishing, Wallingford, UK.

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Field LH, Sandlant GR 2001.The gallery-related ecology of New Zealand tree wetas, Hemideina femorata and Hemideina crassidens (Orthoptera, Anostostomatidae). In: The Biology of Wetas, King Crickets and their Allies (ed LH Field) pp. 243–267. CABI Publishing, Wallingford, UK.

Gibbs G 2001 Habitats and biogeography of New Zealand’s Deinacridine and tusked weta species. In: The Biology of Wetas, King Crickets and their Allies (ed LH Field) pp. 35–57. CABI Publishing, Wallingford, UK.

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