Determinants of occupancy
In winter, local road density was the most important predictor of
occupancy for wolf, with higher road density associated with a lower
probability of wolf occupancy (Fig 2C). This corroborates findings from
Jedrzejewskiet al. (2004) in northern Poland where wolf had higher
occupancy in less disturbed or less fragmented forests. In our study
area, the proportion of forest was not an important predictor of wolf
occupancy in either season, even though multiple studies have found it
to be an important habitat characteristic for wolf (Jedrzejewski et al.,
2004; Zlatanova & Popova, 2013) This may be due to the characteristics
of our study area which is heavily forested (mean proportion forest =
0.78 and 0.75 for winter and autumn monitoring sessions, respectively),
thus forest cover is not a limitation to wolf occurrence. In autumn,
terrain ruggedness was the most important predictor of wolf occupancy;
when terrain ruggedness index was >200 (moderately to
highly rugged areas the probability of wolf occupancy declined steeply
(Figure 2F). This can be explained by the fact that wolf’s main prey
source in Romania, wild boar ((Promberger–Fürpass, 2004; Sin et al.,
2019) was documented to prefer less fragmented areas with large beech
forest stands in autumn and early winter (Fonseca, 2008). Additionally,
red and roe deer, which are also important prey for wolves, are known to
move after the rut season (November - December) to more marginal, less
topographically-fragmented areas that provide connectivity to the lower
winter grounds (Zweifel-Schielly et al., 2009). Proportion of forest was
a positive predictor of lynx occupancy in autumn, which corroborates
other studies that found that lynx occurrence in the Carpathians
decreased at low levels of forest cover (Rozylowicz et al., 2010). Local
road density was also an important predictor of lynx occupancy in
winter, with lynx occupancy positively associated with road density
(Figure 2A). While not heavily documented within the Lynx genus,
other felid species have been known to use roads as travel corridors and
for hunting and movement within their home range (Bailey, 1993; Bragin,
1986; Gordon & Stewart, 2007; Kerley et al., 2002; Matyushkin, 1977;
Rabinowitz et al., 1987). Our results suggest that, in winter, Eurasian
lynx are more likely to occupy areas with higher densities of local
logging roads; these roads, which in our area are mostly unpaved, dirt
roads, may provide easier access to resources within lynx home ranges
due to decreased complexity of terrain and decreased snow depth/harder
snowpack from vehicle travel. We did not observe this relationship with
wildcat, however. Rather, there was a slightly negative relationship
between density of local roads and wildcat occupancy in autumn (Figure
2E) which could be an artifact of body size; most documented examples of
felids utilizing roads for movement within their home ranges was with
larger bodied species (>11 kg). We also did not observe
this relationship in winter however, this is likely an outcome of the
importance of altitude for wildcat occupancy, which has a strong
negative relationship (Figure 2B). Higher altitudes are associated with
greater snow depth, and while lynx are well adapted to move in deep snow
and altitude was not important for lynx occupancy, wildcats have
physical limitations that make travel through deep snow more difficult.
A study in Switzerland had similar findings whereby wildcats moved to
areas free of snow in winter and spring and moved back to high
elevations in summer (Mermod & Liberek, 2002). Similarly, in North
America, the relationship between Canadian lynx (Lynx canadensis )
and bobcat (Lynx rufus ), is mediated by snowpack, with the
distribution of the smaller-bodied species, the bobcat, being limited by
snow depth at the northern edge of its range (Morin et al., 2020; Reed
et al., 2017). Our results for marginal occupancy of lynx, wildcats, and
wolf provide insights into both habitat selection and spatial relations
for these elusive carnivores in Romania. Our results suggest lynx may
use roads for movement and hunting, a practice common for other felids
of similar body size, but not described in this species. Additionally,
we provide further support for previous findings on habitat selection
and occupancy for these three European terrestrial predators.