CSIRO PUBLISHING

www.publish.csiro.au/journals/wr Wildlife Research, 2008, 35, 33–43

The short-term effects of an extensive and high-intensityfire on vertebrates in the tropical savannas of the centralKimberley, northern Australia

Sarah LeggeA,C,D, Stephen MurphyA, Joanne HeathcoteA, Emma FlaxmanA ,John AugusteynB and Marnie CrossmanB

AAustralian Wildlife Conservancy, Mornington Wildlife Sanctuary, PMB 925, Derby, WA 6728, Australia.BQueensland Parks and Wildlife Service, PO Box 3130, North Rockhampton, Qld 4701, Australia.CAustralian National University, Canberra, ACT 0200, Australia.DCorresponding author. Email: sarah@australianwildlife.org

Abstract. We report the effects of an extensive (>7000 km2), high-intensity late-dry-season fire in the central Kimberley, Western Australia, on the species richness and abundance of mammals, reptiles and birds. Five weeks after the fire we surveyed 12 sites (six burnt, six unburnt); each pair of sites was closely matched for soil type and vegetation. The species richness and abundance of mammals and reptiles was greater at unburnt sites, especially for mammals (with a 4-fold difference in abundance between burnt and unburnt sites). There was an indication that reptiles immigrated into unburnt patches, but mammals did not. There were also species-specific responses to the fire: Rattus tunneyi and Pseudomys nanus were much more abundant in unburnt sites, whereas Pseudomys delicatulus was caught in equal numbers at burnt and unburnt sites. Diurnal reptiles were more abundant at unburnt sites, but nocturnal reptiles were equally common at burnt and unburnt sites. Avian species richness and overall abundance was similar between burnt and unburnt patches, although a few species showed preferences for one state or the other. The overall high trapping success for mammals (18% across all sites; 28% in unburnt patches) contrasts with the well documented mammal collapse in parts of northern Australia and seems paradoxical given that our study area has experienced the same increase in fire frequency and extent that is often blamed for species collapse. However, our study area has fewer pressures from other sources, including grazing by large herbivores, suggesting that the effects of these pressures, and their interaction with fire, may have been underestimated in previous studies.

Introduction

A suite of studies in the tropical savannas of northern Australia single hot fire (Woinarski et al. 1999). The effects of particular has revealed widespread declines in a range of taxa, most fire regimes over the longer term are harder to assess, but the notably small to medium-sized mammals (Braithwaite and available evidence suggests substantial differences in the assem-Griffiths 1994, 1996; Maxwell et al. 1996; Woinarski et al. blages of flora and fauna in areas burnt frequently compared 2001; Price et al. 2005), seed-eating birds (Franklin 1999; with areas without fire (Bowman and Fensham 1991; Woinarski Franklin et al. 2005), and fire-sensitive vegetation (Russell- et al. 2004). Smith and Bowman 1992; Bowman and Panton 1993; Russell- In contrast to most savanna-dwelling taxa, there is mounting Smith et al. 2002). The introduction of cattle, cats and, in evidence from descriptive studies that small to medium-sized particular, an increase in the size and frequency of fires are most mammals from diverse taxa including rodents, dasyurids, often implicated (see references above). possums and bandicoots are relatively intolerant of any fire,

Several descriptive studies and some controlled manipulative regardless of timing or intensity (Begg et al. 1981; Kerle and experiments have advanced our understanding of how fire Burgman 1984; Friend 1987; Kerle 1998; Firth et al. 2006). In affects various ecological processes and guilds in the tropical most cases, the declines occurred over the course of a year fol-savannas, including the phenology and population dynamics of lowing the fire (e.g. Begg et al. 1981; Kerle and Burgman woody vegetation, the productivity and composition of the grass 1984), suggesting that the indirect effects on survival and/or layer, and the responses of different faunal groups to fire events reproductive output from increased predation (from lack of and regimes (reviewed in Williams et al. 2003b). Over the short cover), and/or reduced resources (e.g. food, nesting) were more term (several years) many species of amphibians, birds and rep- important than direct fire-related mortality. This pattern is tiles appear resilient to different fire treatments although a few echoed in studies from other parts of the world (Whelan 1995; species show preferences for the extremes. For example, some Torre and Diaz 2004). The Kapalga fire experiment (Andersen granivorous birds preferentially use recently burnt habitats, but et al. 2003) imposed four fire treatments on entire subcatch-some blind snakes (Typhlopidae) may be sensitive to even a ments over five years and also showed that most mammal

© CSIRO 2008 10.1071/WR07016 1035-3712/08/010033

S. Legge et al. 34 Wildlife Research

species react negatively to fire irrespective of its intensity (Corbett et al. 2003). This sensitivity to single fire events may make mammals particularly vulnerable to regimes of extensive and frequent fires, particularly if there are other factors operat-ing that prevent or limit population recovery after fire, such as predation by feral cats.

Although controlled experiments enhance our interpreta-tive confidence, extrapolating the results to the real landscape can be difficult. For experimental and operational reasons, prescribed fire treatments need to be imposed with a regular-ity and uniformity that is improbable in the real landscape. In addition, manipulative fire studies are carried out using small experimental units. The Kapalga experiment was a notable exception, with experimental units of 1500–2000 ha (Andersen et al. 2003). However, these units are still dwarfed by the massive fires that regularly cover areas of several hundred thousand hectares of the tropical savannas, especially in the Kimberley (Fisher et al. 2003; Murphy and Legge 2005).

These two problems can be overcome by ‘natural experi-ments’ (sensu Williams et al. 2003b) that take advantage of an event or combination of events that would be extremely hard to replicate experimentally. An example is the Solar Village study near Darwin (Woinarski et al. 2004), which demonstrated sig-nificant shifts in vegetation and the faunal community in response to 23 years of fire exclusion by the landowners.

It is widely accepted that extensive late-dry-season fires have become more common (Williams et al. 2002; Russell-Smith et al. 2003). Land managers and ecologists alike are concerned about their effects, which are known to include increased tree mortality (Williams et al. 2003a), damage to riparian vegetation (Douglas et al. 2003), and declines in abundance for some species (e.g. bandicoots) (Pardon et al. 2003). However, they are an example of a type of fire that is very difficult to reproduce in controlled experiments. The reasonably hot fires incorporated in some descriptive studies (Begg et al. 1981; Kerle and Burgman 1984) were also not in the league of many of the late-dry-season fires that affect the northern savannas. Williams et al. (1999) took advantage of an unplanned late-dry-season fire to examine its effects on vegetation, but to our knowledge there are no data on the short-term effects of an extensive and intense late-dry-season fire on vertebrates.

In this study, we took advantage of an unplanned, massive late-dry-season fire in the central Kimberley (which affected a total area of over 735000 ha in September 2006) to examine the response of vertebrates to an event that occurs regularly in this region (Fisher et al. 2003; Russell-Smith et al. 2003; Murphy and Legge 2005). Although our study is a post hoc description, we imposed an experimental framework by comparing the ver-tebrate assemblage in the few patches that escaped the fire (dis-persed throughout the fire-affected area) with sites in burnt areas. The unburnt sites were not wetter than surrounding areas, shielded by creeks, rock, or other features; they appeared to have escaped the fire entirely by chance. The paired burnt/unburnt sites were carefully matched for habitat and soil characteristics. Fires of this scale and thoroughness are unlikely to be attempted experimentally, making our approach the only alternative. Paradoxically, the widespread decline of mammals across many parts of northern Australia makes evaluation of the

effects of fire on this group difficult. This is not the case at the study location, where mammal densities are relatively high (S. Legge, unpubl. data).

Methods

Study area and fire characteristics

The study was carried out during 19–23 October 2006 (i.e. ~5 weeks after fire) at Cleanskin Pocket (17.02°S, 126.68°E), in the northern part of Mornington Wildlife Sanctuary in the central Kimberley (Fig. 1). The study area is dominated by various types of open woodlands with a mean annual rainfall of 700 mm (Bureau of Meteorology). The property has an active fire-management program that broadly aims to reduce the size and frequency of fires. However, in September 2006 an extremely large unplanned fire entered the property from the north, sweeping through existing patchworks of early-dry-season burns. At its height, this fire had an 80-km-wide fire front. Before it was extinguished (by Mornington staff), it burnt 736710 ha, of which 84925 ha was on Mornington. MODIS satellite imagery, accessed via North Australia Fire Information website (http://www.firenorth.org.au/nafi/app/init.jsp, verified February 2008), was used to describe general spatial attributes of the fire.

Fig. 1. Location of Mornington Wildlife Sanctuary in the central Kimberley. The boundary of the property is shown in white. The September 2006 fire, which affected a total area greater than 735000 ha, is shown in black. The study was carried out in the fire-affected area of Mornington.

Wildlife Research 35

Aerial transects showed that the fire was very thorough: in 17 km of straight-line transects through the affected area on Mornington, over 96% was burnt. Moreover, unburnt patches were generally very small – the modal width was 10 m and the biggest patch traversed during these transects was 100 m in diameter (S. Legge, unpubl. data).

However, through aerial and ground searches, we found several relatively large, unburnt patches (size 3–50 ha) and selected six of these for the study. Our selection included a cross-section of the major woodland and soil types in this part of the property. We matched these sites with six additional sites in burnt areas that had the same soil and tree profiles (Fig. 2; Table 1). At burnt sites, the grass layer was completely removed, moderately fire-sensitive shrubs had been killed, and the scorch height reached to the canopy. Burnt sites were an average of 1050 m from the next nearest unburnt patch (range 300–3600 m). The 12 sites stretched across 15 km and unburnt sites were distributed throughout the burnt area (i.e. not clustered). Sites were 1–3 km from standing water, and the impact from cattle and feral donkeys was light (assessed from densities of footprints, scats, and knowledge of stocking rates in the area). Prior to the September 2006 fire, all sites last burned in August 2004. Over the last eight years Cleanskin Pocket has burned biannually between May and September with large fires (most fires affect half to all of the area shown in Fig. 2) (Murphy and Legge 2005).

Survey methods

The survey methods followed the standard protocols developed by the Biodiversity Unit of NT Parks and Wildlife Commission (Alaric Fisher, pers. comm.). Survey quadrats (details below) in the unburnt patches were positioned within 100 m of the edge of the patch, so that any edge effects were kept as similar as possi-ble among quadrats.

Mammals and reptiles

Twenty Elliott traps were set around the perimeter of a 0.25-ha square (i.e. with five traps on each side of the square). A medium-sized cage trap was placed at each of the four corners of the square. Eight pitfalls (15-cm-diameter PVC pipe with end-cap; 60 cm deep) were sunk within the 0.25-ha site, arranged in pairs with 20 m of 30-cm-high drift-fence running through each pair. Traps were baited with a mix of oats/peanut butter/honey/vanilla essence and fish oil during the late after-noon, checked each morning, and closed during the day. Pitfalls were left open continuously, and checked twice each day (in the early morning and late afternoon). Sites were operated for three consecutive nights.

We calculated an overall abundance for each species cap-tured at each site. To exclude recaptures from this figure, we clipped small areas of fur on each trapped mammal and marked

Effects of extensive and intense fire on savanna fauna

Fig. 2. Map of the study area, showing locations of sites and geological units. The entire area shown in the map was burnt, leaving a small number of unburnt patches, including at CS12, CS3, CS10, CS11, CS7 and CS9.

36 Wildlife Research S. Legge et al.

the underside of trapped reptiles with an indelible pen. We caught very few frogs because of the time of year (late dry season), and they are not included in this analysis.

Birds

We identified and counted all birds in a 1-ha area surround-ing the trapping site in an instantaneous sample on three con-secutive mornings. These counts were summed to generate an overall abundance for each species. Sites were visited in a dif-ferent order each day.

Vegetation

We checked that the unburnt and burnt sites were well matched floristically and structurally (see Table 1). We esti-mated basal areas (using the Bitterlich method), percentage foliage projected cover and the modal height (visually) for each tree and shrub species in a 360° arc around each of two diago-nal corners of the trapping quadrat, then averaged these two figures.

Unlike the shrub and tree layer, ground cover differed markedly between burnt and unburnt sites. We sampled ground cover by taking 100 paces through the trapping quadrat and noting what lay under each footfall. Burnt sites had a higher pro-portion of bare ground and a lower proportion of perennial grasses (and the perennials sampled were burnt stumps without

crowns). The proportion of litter was similar in burnt and unburnt sites, but the litter in burnt sites was dead leaves from the scorched canopy, whilst the litter in unburnt sites included matted dead grass and forbs. Unburnt sites had a higher number of logs (estimated by counting all logs over 5-cm diameter around the perimeter of the trapping quadrat) (Table 1).

Analysis Mammals and reptiles We examined the data in steps, using a statistical modelling

approach in GENSTAT 8. The models included response data from the same site (e.g. reptile and mammal abundance). To deal with the potential problem of dependency, we fitted linear mixed models with ‘Site’ specified as the random effect. Variance components were estimated using the residual maximum-likelihood method and fixed effects from weighted least-squares. The significance of fixed effects was assessed using Wald statistics. Residual and quantile diagnostic plots were used to check model assumptions.

First, we tested for differences in the species richness and abundance of reptiles and mammals between burnt and unburnt sites, and whether these measures varied with the size of the patch (unburnt sites only). Second, we examined species-specific patterns. We took the three most frequently caught mammals (Rattus tunneyi, Pseudomys nanus, P. delicatulus),

Table 1. The soil, floristics, structure of the woody vegetation, and ground characteristics of each site

Site Fire treatment Modal height Foliage projected Basal area of Ground: Ground: Ground: No. of logs (and size of of dominant cover of trees/shrubs percentage percentage percentage around patch if unburnt) tree species (m) dominant tree (m2 ha–1) bare soil litter perennial, annual, perimeter

forb, other

Sites 1, 9. Corymbia polycarpa on residual sands, with clay horizon at depth Upper storey: C. polycarpa, Eucalyptus pantoleuca, Eucalyptus lirata, Brachychiton diversifolius Shrubs: Acacia stellaticeps, Grevillea pteridifolia, Melaleuca viridiflora, Melaleuca nervosa, Persoonia falcata, Petalostigma pubescens,

Verticordia verticillata CS1 Burnt 12 15 2 67 26 7 2 CS9 Unburnt (3 ha) 15 10 1.5 20 34 56 5

Sites 5, 3. Corymbia polycarpa on fluvial silts of riverine floodplains Upper storey: C. polycarpa, E. pantoleuca, Adansonia gregorii, Corymbia bella, Callitris intratropica Shrubs: A. stellaticeps, Ehretia saligna, G. pteridifolia, Pandanus spiralis, P. falcata, P. pubescens, V. verticillata, G. striata CS5 Burnt 9 10 4.6 79 17 4 1 CS3 Unburnt (12 ha) 12 10 2.3 18 35 47 5

Sites 6, 7. Corymbia pachycarpa on residual sands, with clay horizon at depth Upper storey: C. pachycarpa, E. pantoleuca, E. tectifica, Corymbia terminalis Shrubs: M. viridiflora, G. pteridifolia, Bossiaea bossiaeoides, Grevillea sp. CS6 Burnt 7 10 4.3 65 30 6 4 CS7 Unburnt (14 ha) 6 15 2.3 23 34 43 5

Sites 8, 12. Melaleuca viridiflora on alluvial sands (slope wash) Upper storey: M. viridiflora, M. nervosa, C. polycarpa, E. pantoleuca, B. diversifolius Shrubs: P. pubescens, P. falcata, Santalum lanceolatum, P. spiralis, G. pteridifolia, A. stellaticeps CS8 Burnt 5 40 6.13 51 45 2 9 CS12 Unburnt (7 ha) 4 20 2.5 6 26 68 2

Sites 2, 4, 10, 11. Eucalyptus brevifolia on lateritic, hard-setting red earth Upper storey: E. brevifolia, Eucalyptus tectifica, C. terminalis Shrubs: Dodonaea oxyptera, E. saligna, Carissa spinarum, Melaleuca minutifolia CS2 Burnt 8 25 5.5 58 36 6 4 CS4 Burnt 8 25 4.5 42 53 5 1 CS10 Unburnt (50 ha) 7 30 4.1 11 56 33 9 CS11 Unburnt (50 ha) 7 35 4 6 61 33 15

Effects of extensive and intense fire on savanna fauna Wildlife Research 37

and tested for differences in their abundance at burnt and unburnt sites. Most reptile species were caught too infrequently to carry out an analogous analysis. Instead, we classed reptiles as nocturnal or diurnal and tested for differences in the species richness and abundance of these two groups at burnt and unburnt sites.

Birds Using linear regression models, we tested whether the

species richness and overall abundance of birds differed between burnt and unburnt sites. To explore relationships between individual species and fire, we calculated the propor-tion of the total number for each species that was counted at unburnt sites, and plotted the distribution of these proportions. Species with strong proclivities for unburnt habitat or burnt habitat will have proportions close to 1 or 0 respectively. Species that were recorded at only one or two sites were excluded from this analysis.

In all models, we included the variable ‘Habitat’, based on the dominant tree species at the site (Corymbia polycarpa, C. pachycarpa, Melaleuca viridiflora, Eucalyptus brevifolia).

Figures show the means and standard errors for raw data. Note that where models include a random term, the standard errors in the figures should not be used for inference.

Results Capture success/rate Overall, we caught 153 small mammals of five species (17.8% trap success with 864 trap-nights; Elliott and cage traps com-bined); 77 reptiles of 15 species (26.8% trap success in 288 pitfall-days) (Appendix 1). We counted 800 birds of 59 species (Appendix 2). Recapture rates for mammals and reptiles was similar in burnt and unburnt sites (mammals 23% in burnt, 22% in unburnt sites; reptiles 1% in burnt, 1% in unburnt sites).

Mammals and reptiles

common in unburnt sites but P. delicatulus was equally common in burnt and unburnt sites (Fire × Species: χ2

2 = 23.5; P < 0.001; Fig. 5). Captures of all three species were highest in C. polycarpa and M. viridiflora woodlands, and lower in E. brevifolia and C. pachycarpa woodlands (χ2

3 = 10.1; P < 0.02).

Reptiles – diurnal versus nocturnal There were more diurnal reptile species (i.e. dragons and

skinks) in unburnt sites but the number of nocturnal species (i.e. geckoes) was similar in burnt and unburnt sites (Diurnal/Nocturnal × Fire: χ2

1 = 8.94, P = 0.003) (Fig. 6a). Diurnal reptiles were also more abundant in unburnt plots, whereas the abundance of nocturnal reptiles did not differ between burnt and unburnt sites (Diurnal/Nocturnal × Fire: χ2

1 = 9.05, P = 0.003) (Fig. 6b). Reptile abundance was also 2–3 times higher in C. polycarpa and M. viridiflora woodlands than in C. pachycarpa and E. brevifolia woodlands (χ2 = 7.88,3 P = 0.05), but the species richness was similar among habitats (χ2

3 = 1.25, P = 0.74).

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Mammal Reptile The species richness of both mammals and reptiles was Class

significantly higher in unburnt sites (χ21 = 16.1, P < 0.001) (b)

(Fig. 3a) and did not vary among the four habitats (χ23 = 2.41,

P = 0.49). The abundance of mammals and reptiles was greater in unburnt sites, and this difference was more pronounced for mammals (χ2

1 = 34.3, P < 0.001) (Fig. 3b). There were non-sig-nificant differences among habitats (χ2

3 = 7.52, P = 0.06), with slightly more captures in M. viridiflora and C. polycarpa sites, and fewest in C. pachycarpa sites.

Size of unburnt patches Within the unburnt sites, there were trends for the overall abun-dance of reptiles, but not mammals, to be lower in larger patches. The pattern for species richness was similar but weaker (Fig. 4a, b) (overall abundance: Class × Patch Size χ2

1 = 3.20; P = 0.07; species richness: Class × Patch Size χ2 = 1.55;1 P = 0.21).

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Three species of mammal (R. tunneyi, P. nanus, P. delicatulus) Fig. 3. Species richness (a) and abundance (b) of mammals and reptiles at were captured frequently enough (see Appendix 1) to examine six burnt and six unburnt sites. Bars show means and standard errors for species-specific patterns. R. tunneyi and P. nanus were more sites.

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Birds

The species richness and overall abundance of birds did not differ between burnt and unburnt sites (species richness: F1,11 = 2.15, P = 0.17; abundance: F1,11 = 0.19, P = 0.67). Birds were generally more abundant in E. pachycarpa sites (F3,11 = 5.98, P = 0.02). This was driven by very large numbers of nectarivores on the flowering E. pachycarpa at these sites.

Brown quail (Coturnix ypsilophora), golden-headed cisti-colas (Cisticola exilis) and rufous songlarks (Cincloramphus mathewsi) were overwhelmingly recorded in unburnt sites (i.e. at least 80% of all observations). In contrast, over 80% of the observations for grey-crowned babblers (Pomatostomus tempo-ralis), pallid cuckoos (Cuculus pallidus), magpie-larks (Grallina cyanoleuca) and yellow-throated miners (Manorina flavigula) were recorded in burnt sites (Fig. 7; Appendix 2).

Discussion The data presented here reveal some clear differences in the fauna of burnt and unburnt patches five weeks after an extensive

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and intense fire. Given the careful matching of habitats for burnt/unburnt pairs, it seems reasonable to assume that these differences were caused directly or indirectly by the fire.

Mammals

The species richness and overall abundance of mammals was substantially higher in unburnt remnants within the burnt land-scape. We cannot distinguish between the relative contributions of mortality and immigration (from burnt to unburnt patches) to these differences. However, whereas there was a negative relationship between abundance and patch size for reptiles (sug-gesting some immigration), this was not the case for the mammals, which may have a less flexible social and spacing system. Regardless, it seems inescapable that large numbers of small mammals in the study area died following the fire. Over 96% of the entire study area was intensely burnt, unburnt patches were few, small, and up to 4 km from the next nearest unburnt patch. At best, a small number of animals adjacent to unburnt patches may have moved into these refuges. If mammal abundance at unburnt sites reflects the preburn abundance across the study area, then ~90% of the P. nanus and R. tunneyi populations died within five weeks of the fire.

A growing number of studies report the sensitivity of savanna mammals to fire (Kerle and Burgman 1984; Kerle 1998; Corbett et al. 2003). Most report declines that manifest over the course of a year (Begg et al. 1981; Sutherland and Dickman 1999; Letnic 2003; Pardon et al. 2003), suggesting that the indirect consequences of increased predation and/or reduced resources following fires are more important than direct fire-related mortality. The decline in our study was more rapid. Although the Cleanskin Pocket fire was very extensive it seems unlikely that this increased direct mortality – the three most common mammal species live in burrow systems, and at least one species, P. delicatulus, was apparently unaffected by the fire. The scale and thoroughness of the Cleanskin Pocket fire

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Fig. 4. The relationship between the size of an unburnt patch and the (a) Fig. 5. The abundance of the three most common mammal species in abundance, and (b) species richness, of reptiles and mammals. burnt and unburnt patches. Bars show means and standard errors for sites.

Effects of extensive and intense fire on savanna fauna Wildlife Research 39

may have increased exposure to predators and reduced food resources to an extreme degree, causing relatively rapid declines (see also Green and Sanecki 2006).

In previous studies, R. tunneyi has shown a mixed response to fire, from marked declines with repeated late-dry-season burns (Corbett et al. 2003), to higher abundance with frequent (including late) burns (Woinarski et al. 2004; Price et al. 2005). In our study, this species declined strongly after fire. The diver-sity of responses may relate to the scale and patchiness of fires. R. tunneyi is herbivorous (Braithwaite and Griffiths 1996) and may be able to exploit the fresh grass growth in burnt areas as long as there are patches of unburnt habitat nearby that act as refuges. This may be particularly relevant if rains follow soon after the fire and vegetation regenerates rapidly (for example, in very late dry season and storm burns). P. nanus may be similar – a high proportion of females in the unburnt patches were beginning to breed, suggesting that rapid recovery is possible. Kerle and Burgman (1984) found P. nanus most abundant at

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long-unburnt sites, but noted that the species recolonised a burnt area relatively quickly.

In contrast to the larger rodents, P. delicatulus appears to be resilient to the effects of fire (Braithwaite and Griffiths 1996; Corbett et al. 2003; Kutt and Woinarski 2007). Being small bodied, P. delicatulus may be able to shelter from predators in the meager amount of structure (burnt tussocks, surface irregu-larities, etc) that remain after the fire, and salvage food more efficiently than larger-bodied and more pedestrian species.

Reptiles Reptile species richness and abundance decreased following the Cleanskin Pocket fire, although their response was less strong than for mammals. The reptile fauna has a greater range of for-aging habits and space use, some of which may convey more resilience to the loss of cover. Other studies have similarly shown an overall decrease in the reptile fauna with fire, with heterogeneous species-specific responses that have been attributed to differences in the preferred breeding season, the over-riding influence of moisture, soil and vegetation type, and sensitivity to overheating when vegetation is removed (Braithwaite 1987; Trainor and Woinarski 1994; Masters 1996; Woinarski et al. 1999; Woinarski and Ash 2002). The decline in our study was driven by diurnal skinks and dragons rather than nocturnal geckoes, suggesting that lack of cover is critical – either by causing increased predation by diurnal predators, or overheating risks. This nocturnal/diurnal difference has also been reported from the arid zone (Masters 1996), semiarid zone (James 2003) and higher-rainfall tropical woodlands (Woinarski and Ash 2002).

Birds The effect of the fire on birds in our study was less clear. Species richness and abundance did not differ between burnt and unburnt sites. The Cleanskin Pocket fire was so extensive, and the unburnt patches so few and small, that comparisons of burnt

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Active period Fig. 7. Histogram of the proportion of all observations for each bird

Fig. 6. The species richness (a) and abundance (b) of diurnal and noctur- species that were in unburnt sites. Species seen at only one or two sites have nal reptiles from six unburnt sites and six burnt sites. Bars show means and been excluded. Species at the extreme tails of the distributions are showing standard errors for sites. a preference for burnt or unburnt habitat.

40 Wildlife Research S. Legge et al.

and unburnt habitat may be meaningless in this highly mobile group. However, a few species showed preferences for using burnt or unburnt areas. For example, golden-headed cisticolas, rufous songlarks and brown quail were overwhelmingly recorded from unburnt sites. These patterns have been noted before (Woinarski et al. 1999), and probably arise because these species rely on thick grass cover. At the other extreme, magpie-larks, yellow-throated miners, grey-crowned babblers and pallid cuckoos were all much more prevalent in burnt sites. These species may be taking advantage of foraging opportunities in the open environment. The predilection of pallid cuckoos for burnt areas concurs with one other study in Queensland (Kutt and Woinarski 2007), but contrasts with a second in the Victoria District (Woinarski et al. 1999).

Concluding remarks The generally high capture success for mammals (18% across all sites, and 28% in unburnt patches) is noteworthy. Many sites were peppered with such a high burrow density that walking while setting traps was awkward. In contrast, recent surveys from the Northern Territory indicate massive and widespread declines in the small mammal fauna even in protected areas (Woinarski et al. 2001, 2005; Price et al. 2005; Legge 2006). These declines have been attributed to predation by cats, vege-tation changes caused by introduced herbivores (especially cattle) and, in particular, an increase in the frequency and size of fires. The latter explanation is appealing given the mounting evidence that mammals are sensitive to fire. However, savanna mammals have persisted over geological time in a fire-prone landscape. The recent changes in fire patterns (Williams et al. 2002; Russell-Smith et al. 2003) and the introduction of inter-active effects from grazing (Kutt and Woinarski 2007), weeds, cats et cetera may be directly or indirectly (e.g. through habitat change) affecting the ability of mammal populations to recover after fire events.

Satellite imagery analyses show that Cleanskin Pocket has a history of frequent (i.e. every 2 years), and extensive fires, a pattern that has been implicated in mammal declines elsewhere. Why then, are small mammal numbers so paradoxically high? One potential explanation is the lack of other, interacting environmental pressures. In particular, grazing pressure from large herbivores in Cleanskin Pocket is low and episodic. The cattle in Cleanskin Pocket are an unmanaged male-biased herd and during the dry season they follow the seasonal watercourses downstream and out of the study area. Other large herbivores (buffalo, donkeys, horses and pigs) are extremely few or absent. Fauna surveys on a 65000 ha destocked section of Mornington are showing that the removal of cattle and feral herbivores leads to remarkable recovery in the mammal fauna (S. Legge, unpubl. data). Taken together these observations suggest that the contribution of introduced herbivores to faunal collapse, partic-ularly in combination with altered fire regimes, may have been generally underestimated (Woinarski and Ash 2002; Franklin et al. 2005; Kutt and Woinarski 2007).

The declines of small and medium-sized mammals in tropi-cal Australia are now unequivocal (Braithwaite and Griffiths 1994, 1996; Maxwell et al. 1996; Woinarski et al. 2001, 2005; Price et al. 2005; Legge 2006). They are pervasive and in some areas they are occurring irrespective of the land management

(Price et al. 2005). It is alarming to consider that in the face of this biodiversity crisis, we cannot satisfactorily explain why mammals are disappearing from Kakadu (Woinarski et al. 2001), and yet persisting in an area like Cleanskin Pocket.

Acknowledgements Thanks to Dan Swan and Butch Maher for help with logistics. Alaric Fisher (Tropical Savanna CRC) provided helpful advice on survey design. Constructive comments on the manuscript were gratefully received from John Woinarski, Alan Andersen, Ray Lloyd, Kim Maute, and three review-ers. This study was funded through the generosity of an anonymous sup-porter of the Australian Wildlife Conservancy.

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Manuscript received 9 February 2007, accepted 23 January 2008

42 Wildlife Research S. Legge et al.

Appendix 1. The number of sites at which each mammal and reptile species was captured, and their abundance Burnt and unburnt sites are listed separately

Species Burnt sites Unburnt sites No. of No. of No. of No. of sites captures sites captures

Mammals Leggadina lakedownensis 2 2 2 2 Planigale maculata 1 1 0 0 Pseudomys delicatulus 3 15 6 9 Pseudomys nanus 4 8 6 73 Rattus tunneyi 2 4 6 39 Total 12 30 20 123

Reptiles Amphibolurus gilberti 0 0 1 1 Chlamydosaurus kingii 0 0 1 1 Ctenotus alacer 1 2 1 1 Ctenotus inornatus 0 0 1 4 Ctenotus tantillus 2 6 5 34 Diplodactylus stenodactylus 4 7 2 2 Diporiphora magna 1 1 4 5 Gehyra occidentalis 1 1 0 0 Heteronotia binoei 0 0 1 1 Heteronotia planiceps 1 2 0 0 Menetia greyii 0 0 1 1 Notoscincus ornatus 0 0 2 3 Proablepharus tenuis 2 2 0 0 Ramphotyphlops sp. 0 0 1 1 Strophurus ciliaris 0 0 2 2 Total 12 21 22 56

Effects of extensive and intense fire on savanna fauna Wildlife Research 43

Appendix 2. The number of sites at which each bird species was captured, and their abundance Burnt and unburnt sites are listed separately

Species Common name Burnt Unburnt No. of sites No. counted No. of sites No. counted

Dromaius novaehollandiae Emu 0 0 1 2 Turnix ypsilophora Brown quail 1 10 5 42 Accipiter fasciatus Brown goshawk 0 0 1 1 Falco berigora Brown falcon 1 1 1 1 F. cenchroides Nankeen kestrel 0 0 1 8 Coturnix maculosa Red-backed button-quail 0 0 1 1 Geopelia cuneata Diamond dove 5 19 3 9 G. striata Peaceful dove 4 14 5 17 G. humeralis Bar-shouldered dove 0 0 1 2 Ocyphaps lophotes Crested pigeon 1 3 0 0 Calyptorhynchus banksii Red-tailed black cockatoo 1 2 2 17 Cacatua roseicapilla Galah 0 0 1 3 C. sanguinea Little corella 0 0 1 2 Trichoglossus haematodus Rainbow lorikeet 1 4 1 2 Psitteuteles versicolor Varied lorikeet 1 32 4 31 Aprosmictus erythropterus Red-winged parrot 0 0 1 2 Platycercus venustus Northern rosella 1 2 1 2 Cuculus pallidus Pallid cuckoo 2 5 1 1 Chrysococcyx basalis Horsefield’s bronze-cuckoo 1 1 1 2 Aegotheles cristatus Owlet nightjar 0 0 1 1 Todiramphus sancta Sacred kingfisher 3 5 3 3 T. pyrrhopygia Red-backed kingfisher 3 6 3 4 Merops ornatus Rainbow bee-eater 2 5 5 16 Climacteris melanura Black-tailed treecreeper 2 5 1 4 Malurus melanocephalus Red-backed fairy-wren 4 26 6 28 Pardalotus rubricatus Red-browed pardalote 1 1 0 0 P. striatus Striated pardalote 0 0 2 3 Gerygone olivacea White-throated gerygone 3 7 4 9 Smicornis brevirostris Weebill 5 23 4 22 Philemon citreogularis Little friarbird 5 25 5 26 P. argenticeps Silver-crowned friarbird 0 0 1 2 Manorina flavigula Yellow-throated miner 2 17 1 4 Lichenostomus plumulus Grey-fronted honeyeater 0 0 2 5 Melithrpetus gularis Black-chinned honeyeater 1 2 0 0 Conopophila rufogularis Rufous-throated honeyeater 0 0 1 8 Certhionyx pectoralis Banded honeyeater 2 51 3 58 Lichmera indistincta Brown honeyeater 1 2 0 0 Microeca fascinans Jacky winter 4 10 3 5 Pomatostomus temporalis Grey-crowned babbler 4 25 1 4 Daphoenositta chrysoptera Varied sitella 2 4 0 0 Pachycephala rufiventris Rufous whistler 6 14 5 18 Myiagra rubecula Leaden flycatcher 0 0 1 1 M. inquieta Restless flycatcher 1 1 0 0 Rhipidura leucophrys Willie wagtail 3 10 3 4 Coracina novaehollandiae Black-faced cuckoo-shrike 3 4 1 2 C. papuensis White-bellied cuckoo-shrike 2 3 2 6 Lalage sueurii White-winged triller 3 6 5 8 Oriolus sagittatus Olive-backed oriole 1 2 1 1 Artamus personatus Masked woodswallow 0 0 2 6 A. minor Little woodswallow 1 3 1 3 A. cinereus Black-faced woodswallow 2 4 0 0 Cracticus nigrogularis Pied butcherbird 3 7 1 2 Grallina cyanoleuca Australian magpie lark 2 5 1 1 Mirafra javancia Singing bushlark 3 5 4 6 Taeniopygia bichenovii Double-barred finch 0 0 1 2 Poephila acuticauda Long-tailed finch 3 10 1 4 Dicaeum hirundinaceum Mistletoe bird 0 0 1 1 Cinclorhamphus mathewsi Rufous songlark 0 0 4 4 Cisticola exilis Golden-headed cisticola 0 0 2 3

Total 96 381 114 419

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