Discussion
Cats and
foxes
We predicted that cat and fox activity would be higher in areas burnt by
the prescribed fire, however, we did not find any evidence in support of
this. Whilst some studies have found strong evidence of cat or fox
activity increasing after fire (McGregor et al. 2016a; Miritiset al. 2023), others have found a negative response (Bliege Birdet al. 2018; Lothian et al. 2022), no response (Hradskyet al. 2017c; Moore et al. 2018; Senior et al.2022), or a context-dependent response. For instance, in the USA, swift
foxes (V. velox ), which are closely related to red foxes, only
used burnt areas more frequently if their existing core home ranges were
burnt (Thompson et al. 2008). Indeed, a recent analysis of
existing evidence found that there was a high likelihood of neutral
responses to fire being recorded for both cats and foxes in Australia
(55% and 67%, respectively; Doherty et al. [2023]). One
explanation for our result could be that the prescribed fire in this
study was too mild to illicit an increase in cat or fox activity. A GPS
study of feral cats in northern Australia found that, whilst cats
strongly selected for areas recently burnt by severe fires, they did not
select for areas recently burnt by mild fire—despite these areas
having a high abundance of small mammal prey (McGregor et al.2014). The authors suggested that cats did not benefit from mildly burnt
areas due to unburnt patches likely providing refuge for prey, making
hunting less profitable compared to severely burnt areas (McGregoret al. 2014).
While cats did not increase their activity following the prescribed
fire, they were more active in areas with a shorter time since fire and
lower NDVI—both indicators of simpler vegetation structure (Haslemet al. 2016). Cats also favoured swampy riparian woodlands, which
is typically the most structurally complex vegetation type in our study
area. The seemingly conflicting habitat complexity preferences may be
explained by resource availability. Feral cats are capable of exploiting
a diverse range of habitats, and it is generally considered that they
prefer dense habitats for shelter—such as riparian woodlands—and
more open habitats for hunting (Lozano et al. 2003; Dohertyet al. 2015; Stobo-Wilson et al. 2020). Whilst foraging
efficiency may theoretically be highest in recently burnt areas, these
areas may be sub-optimal, and thus avoided, if prey availability is low
(Pyke et al. 1977). The small mammal population in the eastern
Otway Ranges has been declining for several decades and is now
depauperate (Wayne et al., 2017; Wilson & Aberton, 2006; Wilson et al.,
2001; Wilson et al., 2017; Wilson & Garkaklis, 2020). While we did not
find a relationship between fire and small mammal activity (discussed
below under Small and medium-sized mammals ), the most frequently
detected small mammal species, the bush rat, almost completely avoids
recently burnt areas (Lees et al. 2022). Further, during a
separate, concurrent small mammal study in the eastern Otways, we found
that detections of other small mammal species in burnt areas were very
uncommon (Watchorn, unpublished data). These factors may partially
explain why neither cats nor foxes increased their activity in burnt
areas, and why cat activity was higher in relatively open areas that
likely supported higher prey availability.
We did, however, find that fox activity increased across the study area
after the fire, although due to the proximity of our control and
treatment sites, we cannot be sure if the prescribed fire drove this
change. Juvenile foxes typically disperse in winter (April to June in
this region; Baker et al. 2001), and Hradsky et al. (2017)
also observed an increase in fox activity at their control sites
following a prescribed fire, which was thought to be driven by
dispersing foxes. Spatially independent control sites would have better
isolated the impact of the fire from other factors like seasonal fox
dispersal, however, equipment limitations made such an approach
unfeasible for this study.
We predicted that cat and fox activity would be higher near farms and
towns due to increased resource availability (Hradsky et al.2017c). We found some support for this prediction, with foxes more
active closer to farmland. Across their global range, red foxes, as well
as other generalist mesopredators such as coyotes (Canis latrans )
and golden jackals (C. aureus ), use farmlands due to the
availability of denning habitat, water and food (e.g., livestock,
rodents, human food waste), as well as edge habitats which can support
relatively diverse fauna communities and hunting opportunities
(Gosselink et al. 2003; Šálek et al. 2014; Laux et
al. 2022; Aikawa and Saito 2023). Indeed, we found that the eastern
grey kangaroo, a common prey item of the red fox (Stobo-Wilson et
al. 2022), was also more active near farmlands—likely due to the
availability of pasture for grazing (Arnold et al. 1992; Maguireet al. 2006). In a GPS tracking study, Hradsky et al.(2017c) found that foxes in the Otway Ranges selected for farmland and
forest-farmland interfaces at night, possibly due to livestock carcasses
or prey availability. Collectively, these findings indicate that farm
peripheries could provide effective fox baiting targets for land
managers (Engeman and Linnell 1998; Carter and Luck 2013). Further
high-resolution telemetry and resource mapping studies may provide
further insight into the specific features foxes use (e.g., water dams,
livestock carcasses etc.,), which may further improve bait uptake in
these areas.
Macropods
Fire stimulates a short-term increase in plant nutrients, such as
nitrogen (N), increasing both the nutritional availability and
palatability for herbivores (Eby et al. 2014). This, in turn,
drives temporary increases in the abundance of large herbivores after
fire—a phenomenon observed around the world (Klop et al. 2007;
Raynor et al. 2015; Reid et al. 2023). As such, we
expected eastern grey kangaroos and swamp wallabies to increase their
activity in recently burnt areas. Swamp wallaby activity was higher in
areas with a shorter time since fire, a result consistent with studies
showing this species’ preference for early successional vegetation and
minimal short-term impacts of fire (Styger et al. 2011; Swanet al. 2021; Chard et al. 2022). However, we found no
evidence that macropod activity increased at sites burnt by the
prescribed fire or with Fire extent. Rather, swamp wallaby activity
decreased following the prescribed burn. One explanation for this may be
that the willingness of macropods to forage in recently burnt areas can
vary with predator abundance. For example, Banks (2001) found that
eastern grey kangaroos were more active in open areas were foxes had
been removed, but spent more time near forest edges when foxes were
present. Di Stefano et al. (2009) also found that swamp wallabies
favour more structurally complex vegetation to increase obscurity from
predators, whilst other large herbivores, such as the white-tailed deer
and caribou (Rangifer tarandus ) in North America, also reduce
their use of open areas—despite an abundance of food in those
areas—to reduce the risk of predation (Joly et al. 2003; Cherryet al. 2017).
Small and medium-sized
mammals
The small and medium-sized mammals in our study area typically prefer
dense vegetation, where food and denning resources are greater and the
risk of predation is likely lower (Catling et al. 2001; Dexteret al. 2011). We therefore predicted that the activity of these
groups will be positively associated with NDVI and decrease after the
prescribed fire (White et al. 2022). In support of this
prediction, medium-sized mammal activity decreased with Fire extent, a
trend also seen with medium-sized prey in Europe (Sokos et al.2016), North America (Zwolak and Foresman 2007), and elsewhere in
Australia (Robley et al. 2023). Hradsky et al. (2017a) observed
that fox consumption of medium-sized mammals, such as bandicoots,
doubled after a patchy prescribed fire in the Otways, highlighting the
increased vulnerability of these species to predation following fire,
notwithstanding possible scavenging of carcasses.
Medium-sized mammals also showed a complex relationship with NDVI; while
the main effect of NDVI was generally positive,
activity was negatively
associated with NDVI before the fire and slightly increased afterwards.
This may suggest that these species increased their selection of
microhabitat features associated with higher NDVI (e.g., gullies,
sedges) following the fire (e.g., Swan et al. 2016; Fordyceet al. 2016; Lees et al. 2022). However, the high level of
uncertainty with this interaction limits our ability to draw strong
conclusions. Notably, while higher NDVI is typically associated with
higher species richness for the mammals comprising this species group
(Youngentob et al. 2015b; Dorph et al. 2021; Whiteet al. 2022), individually, these species have exhibited positive
(Miritis et al. 2020; White et al. 2022), negative (Ralph
2021), and neutral (Youngentob et al. 2015b; Hale et al.2016) responses to NDVI. These varied relationships are likely due to
factors such as drought, fire history, and habitat type (Youngentobet al. 2015a; White et al. 2022). Nonetheless, our
findings suggest that NDVI may be a useful means of identifying and
conserving productive and structurally complex areas which may
facilitate mammal occurrence and diversity in this landscape (Sukmaet al. 2019; Rivarola 2022), especially following disturbances
such as drought (White et al. 2022), plant pathogen spread (Casey
2022), or fire (Dorph et al. 2021).
None of the variables predicted the activity of small mammals, a finding
at odds with previous studies on these species that identified
relationships with NDVI (Hale et al. 2016; Chadwick et al.2022) and changes in habitat use following fire (Swan et al.2016; Fordyce et al. 2016; Lees et al. 2022). One reason
for this discrepancy may be that our camera arrangement, in terms of
both density and spatial extent, was insufficient to reliably detect
discrete patterns of microhabitat use for these species, especially
considering the depauperate state of the small mammal community (Wilson
and Garkaklis 2020). The incorporation of fine-scale, site-level habitat
information—such as understorey vegetation structure (e.g., Hradskyet al. 2017a; Lees et al. 2022)—may have further
improved our ability to detect any potential response to fire or
vegetation structure.
Conclusions
We found little evidence to support our predictions that cat, fox, and
macropod activity would increase following the prescribed burn, or that
small mammal (<800 g) activity would decrease. Medium-sized
mammals were negatively associated with Fire extent, and other studies
in the region have identified similar trends following patchy prescribed
burns, along with increased consumption of these species by foxes
(Hradsky et al. 2017a). This suggests that these species may be
particularly vulnerable to fire and invasive predators in this region,
and may benefit from preserving large unburnt refuges and from targeted
post-fire interventions to reduce predation, such as the provision of
artificial refuges (Watchorn et al. 2022).
Looking forward, there are several key research questions which should
be prioritised to conserve fauna inside protected areas. The majority of
evidence demonstrating increases in cat activity post-fire comes from
Australia’s tropical north (Doherty et al. 2023). It remains
unclear whether cats or foxes temporarily adjust their core home range
or move long distances to hunt in recently burnt areas in the temperate
forests, woodlands, and other ecosystems of southern Australia. Whilst
camera traps are useful, their appropriateness for answering this
question is limited by their inherently patchy spatial coverage across
the landscape, as well as the delay associated with deploying them
immediately after prescribed fires, especially in temperate forests. To
this end, we recommend future studies employ the BACI experimental
framework with animal-borne GPS loggers (Le Pla et al. 2023).
This will improve our understanding of the fine-scale movements and
habitat use of cats, foxes, and native prey species immediately before
and after prescribed fire (e.g., McGregor et al. 2014).
Animal-born video cameras could also provide valuable insight into cat
and fox hunting success and prey selection (McGregor et al.2015). These approaches, whilst challenging to implement, will allow for
a more nuanced understanding of fine-scale responses to prescribed fire,
thereby informing more effective management strategies within protected
areas.