In our work, we showed that the probability of occurrence of the crested porcupine in an urban ecosystem was positively correlated to increasing coverage of cultivations and scrublands. The crested porcupine is a monogamous species who pair for life and show a sedentary behaviour after dispersal and settlement in a territory (Mori et al. 2016); therefore, the movements of adults are mostly determined by food search and not by mate search (Lovari et al. 2013; Mazzamuto et al. 2019). This may provide support to the importance of cultivations within urban environments, which provide porcupines with clumped and abundant food resources (Lovari et al. 2017), even within human settlements. Scrublands are mostly selected as den sites, particularly where human pressure (i.e. poaching risk) is highest, which may support the use of this habitat types in dense human settlements (Tinelli and Tinelli 1980; Monetti et al. 2005; Lovari et al. 2017).
Accordingly, within the Rome urban area, the few dens of crested porcupines whose location is known, occur in one archaeological area (“Catacombe di Priscilla”, n = 1; Grano 2016), as well as in a semi-natural scrubland area within a protected natural reserve (n = 2), and in a densely vegetated area of a large recreational park (n = 1; Ancillotto L. pers.
In natural habitats, the crested porcupine mainly feeds on underground storage organs of plants (e.g. bulbs, tubers and rhizomes), but can also eat fruits and vegetables (Bruno and Riccardi 1995; Mori et al. 2020). Crested porcupines may exploit nearby cultivated areas which provide easy access to food resources (e.g. figs and pumpkins) and do not require time-consuming active excavation which may limit vigilance (Lovari et al. 2017). Most likely, the positive correlation between cultivations and occupancy in the urban environment could also be explained by limited food resources in some areas of the city (e.g. recreational parks characterised by deeply modified floras), thus leading porcupine individuals to expose themselves to open and, therefore, risky habitats. Accordingly, few data occurred in recreational areas, possibly underused to limit encounters with humans and potential natural predators, e.g. red foxes and domestic dogs, which are often abundant in urban parks in Rome (Amori et al. 2009).
Local high densities of wild boar (Todini and Crosti 2020) may also limit the occupancy by the crested porcupines in some areas (Mazzamuto et al.
2019). Furthermore, artificial lights at night may limit the use of these areas by crested porcupines, which are known to avoid bright areas and bright moonlight nights (Mori et al. 2014b). In fact, it is much more likely that these areas, as well as archaeological sites, wetlands, and human settlements, are avoided as not providing sufficient food resources. Therefore, all these habitats are avoided by porcupines also in natural contexts, yet some individuals, especially sub-adults, may visit them occasionally and create temporary or seasonal burrows (Pigozzi and Patterson 1990; Börger 2002; Mori and Assandri 2019). Noise pollution and vehicular traffic have also been reported to alter the spatial behaviour of the porcupine (Mori et al. 2013; Mori 2017), and long-distance roads are known to hinder wildlife movements (Forman and Alexander 1998; Seidler et al. 2015).
Accordingly, records of crested porcupines in Italian urban areas increase when vehicular traffic is the lowest (e.g.
during the lockdown following the SARS-CoV 2 pandemic outbreak: Manenti et al. 2020). In this context, the ring highway in Rome may represent a barrier to the transit of porcupines, as green corridors between green areas inside and outside the city centre are few.
Crop damages by crested porcupines may occur in areas covered by cultivations, including vegetable gardens, potentially triggering conflict with humans (Sforzi et al. 1999; Laurenzi et al., 2016). No conflict between humans and porcupines has been reported in Rome to date though; strictly nocturnal habits may have in fact promoted coexistence between porcupines and humans in urban and suburban areas (Lovari et al. 2017), as evidenced in the closely related Indian crested porcupine Hystrix indica in Israel (Sever and Mendelssohn 1989). However, the intense illumination of the highway between Haifa and Tel-Aviv (National Road 2, Israel) did not prevent Indian porcupines from foraging in the nearby of the roadside, contrary to what expected from a nocturnal species that avoids brightest nights (Sever and Mendelssohn 1989).
Our results highlight that a large rodent such as H. cristata may thrive in a urban area by occupying spots of suitable habitats, namely represented by patches of natural or agricultural areas, eventually persisting in one of the largest metropolitan areas in southern Europe. The behavioural and physiological mechanisms that allow such persistence without eliciting conflicts, as well as whether urban populations exhibit gene flow with nearby non-urban ones, is still to be cleared. Thus, the urban population of H. cristata in Rome provides a suitable study system to furtherly shed light on mechanisms and consequences of synurbization in mammals.