Native species exhibit physiological habituation to invaders: a reason for hope.

Animals cope with environmental perturbations through the stress response, a set of behavioural and physiological responses aimed to maintain and/or return to homeostasis and enhance fitness. Vertebrate neuroendocrine axis activation in response to environmental stressors can result in the secretion of glucocorticoids (GCs), whose acute increases may be adaptive, while chronic elevation may be detrimental. Invasive grey squirrels (Sciurus carolinensis) act as a stressor eliciting elevation of GCs in native red squirrels (Sciurus vulgaris). Here we used 6-year data of variation in faecal glucocorticoid metabolite (FGM) concentrations following invasion by grey squirrels in three red squirrel populations, to identify if red squirrels showed physiological habituation to this stressor. The decrease in FGMs over time was more pronounced shortly after invasion and at high densities of grey squirrels while it decreased less strongly and was no longer influenced by the invader density as time since invasion elapsed. At the individual level, FGMs also decreased more markedly as each red squirrel experienced prolonged contact with the invader. Our study provides compelling new data suggesting that native species in the wild can habituate to prolonged contact with invasive species, showing that they may avoid the potentially harmful effects of chronic elevations in GCs.

Invasive alien species as an environmental stressor and its effects on coping style in a native competitor, the Eurasian red squirrel.

Free-living animals cope with environmental stressors through physiological and behavioural responses. According to the unidimensional model, these responses are integrated within a coping style: proactive individuals (bold, active-explorative and social) have a lower hypothalamic-pituitary-adrenal (HPA) axis reactivity than reactive ones (shy, less active-explorative, less social). These associations may change when individuals are exposed to human-induced rapid environmental change (HIREC), such as the introduction of invasive alien species (IAS). Here, we studied Eurasian red squirrels to investigate the relationship between personality traits and one integrated measure of HPA axis activity, both in areas uncolonized (natural populations) and colonized by an IAS, the Eastern grey squirrel (invaded populations). We expected an association between physiological and behavioural responses, and that activity, exploration and social tendency would covary, forming a behavioural syndrome in natural populations, while competition with the IAS was predicted to disrupt these associations. We used faecal glucocorticoid metabolites (FGMs) as an integrated measure of adrenocortical activity, and measured the levels of four personality traits (exploration, activity, activity-exploration and social tendency) with an open field test and a mirror image stimulation test. We found no correlation between FGMs and personality traits, neither in natural nor invaded populations. However, we found correlations among personality traits in areas without interspecific competition, indicating a behavioural syndrome, which was disrupted in invaded populations. This is one of the few studies showing that an IAS, acting as an environmental stressor, alters a native species' behavioural syndrome, but does not influence its coping style.

Personality traits, sex and food abundance shape space use in an arboreal mammal.

Animal space use is affected by spatio-temporal variation in food availability and/or population density and varies among individuals. This inter-individual variation in spacing behaviour can be further influenced by sex, body condition, social dominance, and by the animal's personality. We used capture-mark-recapture and radio-tracking to examine the relationship between space use and personality in Eurasian red squirrels (Sciurus vulgaris) in three conifer forests in the Italian Alps. We further explored to what extent this was influenced by changes in food abundance and/or population density. Measures of an individual's trappability and trap diversity had high repeatability and were used in a Principal Component Analysis to obtain a single personality score representing a boldness-exploration tendency. Males increased home-range size with low food abundance and low female density, independent of their personality. However, bolder males used larger core-areas that overlapped less with other males than shy ones, suggesting different resource (food, partners) utilization strategies among personality types. For females, space use-personality relationships varied with food abundance, and bolder females used larger home ranges than shy ones at low female density, but the trend was opposite at high female density. Females' intrasexual core-area overlap was negatively related to body mass, with no effect of personality. We conclude that relationships between personality traits and space use in free-ranging squirrels varied with sex, and were further influenced by spatio-temporal fluctuations in food availability. Moreover, different personality types (bold-explorative vs. shy) seemed to adopt different space-use strategies to increase access to food and/or partners.

Spillover of an alien parasite reduces expression of costly behaviour in native host species.

Understanding the effects of invasive alien species (IAS) on native host-parasite relationships is of importance for enhancing ecological theory and IAS management. When IAS and their parasite(s) invade a guild, the effects of interspecific resource competition and/or parasite-mediated competition can alter existing native host-parasite relationships and the dependent biological traits such as native species' behaviour. We used a natural experiment of populations of native red squirrels Sciurus vulgaris that were colonized by the alien grey squirrel Sciurus carolinensis, comparing repeated measurements of red squirrel parasite infection and personality with those taken in sites where only the native species occurred. We explored two alternative hypotheses: (a) individual differences in personality traits (activity and/or sociability) of native red squirrel positively affect the probability of macroparasite spillover and thus the likelihood to acquire the alien's parasitic helminth Strongyloides robustus; (b) the combined effects of grey squirrel presence and parasite infection result in a reduction of costly personality traits (activity and/or exploration). Using data from 323 arena tests across three experimental (native species and IAS) and three control sites (only native species), we found negative correlations between native species' activity and infection with S. robustus in the sites invaded by the alien species. Activity was also negatively correlated with infection by its native helminth Trypanoxyuris sciuri but only when grey squirrels were present, while in the red-only sites there was no relationship of T. sciuri infection with any of the personality traits. Moreover, individuals that acquired S. robustus during the study reduced their activity after infection, while this was not the case for animals that remained uninfected. Our results show that parasite-mediated competition is costly, reducing activity in individuals of the native species, and altering the native host-native parasite relationships.

Hydrogen isotopes reveal evidence of migration of Miniopterus schreibersii in Europe.

BACKGROUND: The Schreiber's bat, Miniopterus schreibersii, is adapted to long-distance flight, yet long distance movements have only been recorded sporadically using capture-mark-recapture. In this study, we used the hydrogen isotopic composition of 208 wing and 335 fur specimens from across the species' European range to test the hypothesis that the species migrates over long distances. RESULTS: After obtaining the hydrogen isotopic composition (δ2H) of each sample, we performed geographic assignment tests by comparing the δ2H of samples with the δ2H of sampling sites. We found that 95 bats out of 325 showed evidence of long-distance movement, based on the analysis of either fur or wing samples. The eastern European part of the species range (Greece, Bulgaria and Serbia) had the highest numbers of bats that had moved. The assignment tests also helped identify possible migratory routes, such as movement between the Alps and the Balkans. CONCLUSIONS: This is the first continental-scale study to provide evidence of migratory behaviour of M. schreibersii throughout its European range. The work highlights the need for further investigation of this behaviour to provide appropriate conservation strategies.

Stress in biological invasions: Introduced invasive grey squirrels increase physiological stress in native Eurasian red squirrels.

Invasive alien species can cause extinction of native species through processes including predation, interspecific competition for resources or disease-mediated competition. Increases in stress hormones in vertebrates may be associated with these processes and contribute to the decline in survival or reproduction of the native species. Eurasian red squirrels (Sciurus vulgaris) have gone extinct across much of the British Isles and parts of Northern Italy following the introduction of North American invasive grey squirrels (Sciurus carolinensis). We extracted glucocorticoid metabolites from faecal samples to measure whether the presence of the invasive species causes an increase in physiological stress in individuals of the native species. We show that native red squirrels in seven sites where they co-occurred with invasive grey squirrels had glucocorticoid concentrations that were three times higher than those in five sites without the invasive species. Moreover, in a longitudinal study, stress hormones in native red squirrels increased after colonisation by grey squirrels. When we experimentally reduced the abundance of the invasive grey squirrels, the concentration of faecal glucocorticoid metabolites in co-occurring red squirrels decreased significantly between pre- and postremoval periods. Hence, we found that the invasive species acts as a stressor which significantly increases the concentrations of glucocorticoids in the native species. Given that sustained elevations in glucocorticoids could reduce body growth and reproductive rate, our results are consistent with previous studies where the co-occurrence of the invasive grey squirrel was associated with smaller size and lower reproductive output in red squirrels.

Biodiversity threats from outside to inside: effects of alien grey squirrel (Sciurus carolinensis) on helminth community of native red squirrel (Sciurus vulgaris).

Biological invasions are among the major causes of biodiversity loss worldwide, and parasites carried or acquired by invaders may represent an added threat to native species. We compared gastrointestinal helminth communities of native Eurasian red squirrels (Sciurus vulgaris) in the presence and absence of introduced Eastern grey squirrels (Sciurus carolinensis) to detect alterations induced by the alien species. In particular, we investigated whether spillover of a North American nematode Strongyloides robustus occurs and whether prevalence of a local parasite Trypanoxyuris sciuri in red squirrels is affected by grey squirrel presence. The probability of being infected by both parasites was significantly higher in areas co-inhabited by the alien species, where 61 % of examined red squirrels (n = 49) were infected by S. robustus and 90 % by T. sciuri. Conversely, in red-only areas, the two parasites infected only 5 and 70 % of individuals (n = 60). Overall, our findings support the hypothesis that red squirrels acquire S. robustus via spillover from the alien congener and suggest that invaders' presence may also indirectly affect infection by local parasites through mechanisms diverse than spill-back and linked to the increased competitive pressure to which red squirrels are subjected. These results indicate that the impact of grey squirrel on red squirrels may have been underestimated and highlight the importance of investigating variation in macroparasite communities of native species threatened by alien competitors.

Dangerous neighbours: Birds and bird-eating bats sharing tree cavities.

Mounting evidence indicates the non-consumptive effects of predators significantly impact prey physiology, ecology and behaviour. Passerine birds experience adverse effects on nesting and reproductive success when in proximity to predators. Fear of predators is context-dependent and influenced by hunting habitats and foraging strategies. While some bat species prey on birds, the greater noctule (Nyctalus lasiopterus) stands out by specialising in avian prey, especially during peak bird migration. N. lasiopterus is thought to seize avian prey in flight, but direct evidence is lacking. If birds were taken from nests, they would likely avoid nesting near these bats. However, no observations support this view. This study documents the successful reproduction of Eurasian blue tits (Cyanistes caeruleus) nesting alongside a colony of approximately 25 greater noctules. This bird species is a prey species for greater noctules in Italy. Over about 1 month (April-May 2023), we observed parent birds provisioning food to chicks, with at least two chicks alive and fed outside the tree cavity by the end of the period. While acknowledging the limitations of a single observation, we propose that this previously unknown behaviour indirectly supports the idea that greater noctules only capture avian prey in flight, not within confined spaces. This observation challenges the perception that these bats pose a threat when sharing roosting spaces in trees, as evidenced in our observed case. We hope this novel observation inspires future research on variations in bird nesting behaviour and reproductive success in the presence of bird-eating bats, as well as an assessment of the long-term impact on population dynamics and reproductive success of nesting birds sharing such roosting spaces.

Use of infrared thermography to detect reactions to stressful events: does animal personality matter?

The study of the relationship between animal stress and personality for free-ranging animals is limited and provides contrasting results. The perception of stressors by an individual may vary due to its personality, and certain personality traits may help individuals to better cope with them. Using non-invasive infrared thermography (IRT), we investigated the link between physiological and behavioral components expressed during an acute stress event by free-ranging Fremont's squirrels (Tamiasciurus fremonti). We expected that, during the acute stress event of being approached by the researcher, individuals that showed a fast pace-of-life syndrome (bolder, more active, and less social/more aggressive) based on an arena test would exhibit stronger sympathetic-adrenal-medullary system reactivity showing a more intense stress-induced hyperthermia (high core body temperature and low peripheral temperature) than individuals with a slow pace of life (shy, less active, and more social). We successfully employed IRT technology to images of Fremont's squirrels with identification of the individuals' body parts (eye, nose, ear, hind foot). However, we found no support for our hypothesis. Squirrels' body surface temperatures told us more about a squirrel's external environment and less about the thermal state of the body in that environment following a stressful event. Further studies need to assess how to make IRT effective and efficient in the field and improve its performance in studying the relationships between physiology and personality in wildlife.

Physiological stress response to urbanisation differs between native and invasive squirrel species.

Novel pressures derived from urbanisation can alter native habitats and ultimately impact wildlife. Coping with such human-driven changes might induce shifts in species phenotypic traits, such as physiological responses to anthropogenic stressors. Preadaptation to face those challenges has been suggested to favour settlement and spread of invasive alien species in urbanised areas which, consequently, might respond differently than ecologically similar native species to stressors posed by urbanisation. The activation of the hypothalamic-pituitary-adrenal (HPA) axis and the subsequent release of glucocorticoids (GCs) has been suggested to mediate responses to anthropogenic disturbance in vertebrates. Furthermore, intraspecific competition, in conjunction with stressors related to urbanisation, might affect invasive and native species physiological stress responses differently. Using a parallel pseudo-experimental study system we measured faecal glucocorticoid metabolite (FGM) concentrations of the native Eurasian red squirrel and the invasive alien Eastern grey squirrel along a rural-urban gradient and in relation to conspecific density. The two species responded differently to challenges posed by the synergic effect of urbanisation and intraspecific competition. Association of FGMs and conspecific density in native red squirrels varied between rural and suburban sites, potentially depending on differential HPA axis responses. In urban sites, this relationship did not differ significantly from that in rural and suburban ones. Conversely, invasive grey squirrels' FGMs did not vary in relation to conspecific density, nor differed along the rural-urban gradient. Improving knowledge about native and competing invasive species' physiological responses to anthropogenic stressors can support conservation strategies in habitats altered by man. Our findings suggested that the invasive squirrels might be preadapted to cope with these challenges in urbanised areas, potentially increasing their success under the future global change scenario.

Climate is changing, are European bats too? A multispecies analysis of trends in body size.

Animal size, a trait sensitive to spatial and temporal variables, is a key element in ecological and evolutionary dynamics. In the context of climate change, there is evidence that some bat species are increasing their body size via phenotypic responses to higher temperatures at maternity roosts. To test the generality of this response, we conducted a >20-year study examining body size changes in 15 bat species in Italy, analysing data from 4393 individual bats captured since 1995. In addition to examining the temporal effect, we considered the potential influence of sexual dimorphism and, where relevant, included latitude and altitude as potential drivers of body size change. Contrary to initial predictions of a widespread increase in size, our findings challenge this assumption, revealing a nuanced interplay of factors contributing to the complexity of bat body size dynamics. Specifically, only three species (Myotis daubentonii, Nyctalus leisleri, and Pipistrellus pygmaeus) out of the 15 exhibited a discernible increase in body size over the studied period, prompting a reassessment of bats as reliable indicators of climate change based on alterations in body size. Our investigation into influencing factors highlighted the significance of temperature-related variables, with latitude and altitude emerging as crucial drivers. In some cases, this mirrored patterns consistent with Bergmann's rule, revealing larger bats recorded at progressively higher latitudes (Plecotus auritus, Myotis mystacinus, and Miniopterus schreibersii) or altitudes (Pipistrellus kuhlii). We also observed a clear sexual dimorphism effect in most species, with females consistently larger than males. The observed increase in size over time in three species suggests the occurrence of phenotypic plasticity, raising questions about potential long-term selective pressures on larger individuals. The unresolved question of whether temperature-related changes in body size reflect microevolutionary processes or phenotypic plastic responses adds further complexity to our understanding of body size patterns in bats over time and space.

COVID-19 could accelerate the decline in recreational hunting: A natural experiment from Northern Italy.

Although many studies highlighted the potential of COVID-19 to reshape existing models of wildlife management, empirical research on this topic has been scarce, particularly in Europe. We investigated the potential of COVID-19 pandemic to accelerate the ongoing decline in an aging population of recreational hunters in Italy. Namely, we modelled spatiotemporal trends between 2011 and 2021 in the number of recreational hunters in 50 Italian provinces with a varying incidence of COVID-19, and temporally delayed waves of infection. Compared to projections from 2011-2019 data, we detected a lower number of hunters who enrolled for the hunting season, both in 2020 (14 provinces) and in 2021 (15 provinces). The provinces with the highest incidence of COVID-19 in the Lombardy and Emilia-Romagna regions were also those experiencing the most marked decrease in hunting participation. Our findings revealed that a wildlife management system based on recreational hunting can be rapidly destabilized by epidemics and their associated public health measures, particularly when the average age of hunters is high, like in Italy. Considered the high incidence attained by COVID-19 in many European countries, where hunters are pivotal for the management of large ungulates and where they were already declining before the pandemic, our findings call for further large-scale research about the impact of COVID-19 on hunting participation.

Phylogeography and postglacial recolonization of Europe by Rhinolophus hipposideros: evidence from multiple genetic markers.

The demographic history of Rhinolophus hipposideros (lesser horseshoe bat) was reconstructed across its European, North African and Middle-Eastern distribution prior to, during and following the most recent glaciations by generating and analysing a multimarker data set. This data set consisted of an X-linked nuclear intron (Bgn; 543 bp), mitochondrial DNA (cytb-tRNA-control region; 1630 bp) and eight variable microsatellite loci for up to 373 individuals from 86 localities. Using this data set of diverse markers, it was possible to determine the species' demography at three temporal stages. Nuclear intron data revealed early colonization into Europe from the east, which pre-dates the Quaternary glaciations. The mtDNA data supported multiple glacial refugia across the Mediterranean, the largest of which were found in the Ibero-Maghreb region and an eastern location (Anatolia/Middle East)-that were used by R. hipposideros during the most recent glacial cycles. Finally, microsatellites provided the most recent information on these species' movements since the Last Glacial Maximum and suggested that lineages that had diverged into glacial refugia, such as in the Ibero-Maghreb region, have remained isolated. These findings should be used to inform future conservation management strategies for R. hipposideros and show the power of using a multimarker data set for phylogeographic studies.

Macroparasite community of the Eurasian red squirrel (Sciurus vulgaris): poor species richness and diversity.

The Eurasian red squirrel (Sciurus vulgaris) is the only naturally occurring tree squirrel throughout its range. We aim at improving current knowledge on its macroparasite fauna, expecting that it will have a poor parasite diversity because in species that have no sympatric congeners parasite richness should be lower than in hosts sharing their range with several closely related species, where host-switching events and lateral transmission are promoted. We examined gastro-intestinal helminth and ectoparasite communities (excluding mites) of, respectively, 147 and 311 red squirrel roadkills collected in four biogeographic regions in Italy and France. As expected, the macroparasite fauna was poor: we found five species of nematodes and some unidentified cestodes, three fleas, two sucking lice and two hard ticks. The helminth community was dominated by a single species, the oxyurid Trypanoxyuris (Rodentoxyuris) sciuri (prevalence, 87%; mean abundance, 373 ± 65 worms/host). Its abundance varied among seasons and biogeographic regions and increased with body mass in male hosts while decreased in females. The most prevalent ectoparasites were the flea Ceratophyllus (Monopsyllus) sciurorum (28%), whose presence was affected by season, and the generalist tick Ixodes (Ixodes) ricinus that was found only in France (34%). All the other helminths and arthropod species were rare, with prevalence below 10%. However, the first record of Strongyloides robustus, a common nematode of North American Eastern grey squirrels (S. carolinensis), in two red squirrels living in areas where this alien species co-inhabits, deserves further attention, since low parasite richness could result in native red squirrels being particularly vulnerable to parasite spillover.

Living on the edge: morphological and behavioral adaptations to a marginal high-elevation habitat in an arboreal mammal.

Habitats are characterized by different local environmental conditions that influence both behavior and morphology of species, which can result in habitat-dependent phenotypic differences among animals living in heterogeneous environments. We studied 3 alpine populations of Eurasian red squirrels (Sciurus vulgaris), 1 living in a marginal high-elevation habitat at the edge of the species' altitudinal distribution, and 2 occurring in higher-quality habitats. Here, we investigated whether squirrels living in the marginal area differed in 2 morphological parameters (body size and body mass) and/or in the expression of 4 personality traits estimated with an open field test and a mirror image stimulation test (activity, exploration, activity-exploration, and social tendency). Furthermore, we tested whether within-individual variance of the traits (behavioral plasticity) was higher in the edge habitat. Male squirrels in the edge habitat were smaller and weighed less than in the other study areas, while among females, size-habitat relationships were less marked. These sex-specific patterns were explained by a strong association between body mass and reproductive success in female squirrels. Squirrels in the marginal habitat were more active, explorative, and had a more social personality than in the other habitats. However, in contrast to our predictions, behavioral plasticity was smaller in the marginal habitat, but only for the trait exploration. Our results suggest that animals choose the habitat that best fits their personality, and that habitat-related differences in selective pressures may shape animals' morphology.

Lost and found: Helminths infecting invasive raccoons introduced to Italy.

North American raccoons (Procyon lotor) have been introduced to several European countries, where they may represent a sanitary threat as hosts of several pathogens such as the zoonotic ascarid Baylisascaris procyonis. We carried out parasitological analysis on raccoons introduced to Italy to verify whether the species had carried along B. procyonis or any other gastro-intestinal helminths that may threaten humans, livestock or native wildlife. We examined 64 raccoons culled in Northern Italy during control activities and 3 roadkills opportunistically sampled from a separate population located in central Italy. Helminths were collected from the gastro-intestinal tract through standard parasitological techniques and identified based on a combination of morphology and molecular methods. Overall, examined raccoons showed a poor parasitic fauna, with almost 30% of individuals free of any helminth infection. The most prevalent species were the nematodes Strongyloides procyonis (26.9%), Aonchotheca putorii (25.4%) and Porrocaecum sp. (19.4%). Plagiorchis sp. trematodes were also common (13.4%), whereas cestodes were scarcely represented. With the exception of S. procyonis introduced from North America, all the other identified taxa have either a Eurasian or a wide Holarctic distribution. Despite not finding any B. procyonis in the examined raccoons, passive surveillance for this parasite should be implemented, especially in Tuscany, since the limited host sample examined in the present survey does not allow to exclude its presence.

Camera Trapping to Assess Status and Composition of Mammal Communities in a Biodiversity Hotspot in Myanmar.

Tropical forests comprise a critically impacted habitat, and it is known that altered forests host a lower diversity of mammal communities. In this study, we investigated the mammal communities of two areas in Myanmar with similar environmental conditions but with great differences in habitat degradation and human disturbance. The main goal was to understand the status and composition of these communities in an understudied area like Myanmar at a broad scale. Using camera trap data from a three-year-long campaign and hierarchical occupancy models with a Bayesian formulation, we evaluated the biodiversity level (species richness) and different ecosystem functions (diet and body mass), as well as the occupancy values of single species as a proxy for population density. We found a lower mammal diversity in the disturbed area, with a significantly lower number of carnivores and herbivores species. Interestingly, the area did not show alteration in its functional composition. Almost all the specific roles in the community were present except for apex predators, thus suggesting that the effects of human disturbance are mainly effecting the communities highest levels. Furthermore, two species showed significantly lower occupancies in the disturbed area during all the monitoring campaigns: one with a strong pressure for bushmeat consumption and a vulnerable carnivore threatened by illegal wildlife trade.

Complex relationships between physiological stress and endoparasite infections in natural populations.

Short-term elevation of glucocorticoids (GCs) is one of the major physiological mechanisms by which vertebrates cope with challenging environmental or social factors (stressors). However, when exposure to stressors occurs repeatedly or over a prolonged period of time, animals may experience chronic elevation of GCs, which reduces the immune response efficiency and can lead to higher intensity of parasitic infection. Here, we used invasive gray squirrels Sciurus carolinensis introduced in Northern Italy and their 2 most prevalent gastrointestinal parasites, the nematode Strongyloides robustus and coccidia of the genus Eimeria, as a model to investigate relationships among macroparasite infection and concentrations of fecal glucocorticoid metabolites (FGMs), an integrated measure of circulating GCs. Our results revealed an association of FGMs with infection by St. robustus, but not with coccidia. Individuals with higher FGMs appear to be responsible for the greatest St. robustus egg shedding within gray squirrel populations, thus possibly acting as superspreaders. However, FGMs were negatively associated with adult St. robustus, suggesting that the abundance of adults of this nematode species does not induce elevation in FGMs, but is only affected by it through immune-mediated effects on its fecundity. Finally, the relationship between St. robustus (both eggs and adult parasites) and FGMs was not linear, suggesting that only high levels of physiological stress influence parasite infection. Our findings highlight that the direction and magnitude of the stress-infection relationship may depend not only on the specific host-parasite system, but also on the different life stages of the same parasite.

Relationships between personality traits and the physiological stress response in a wild mammal.

Glucocorticoids (GCs) are involved in the regulation of an animal's energetic state. Under stressful situations, they are part of the neuroendocrine response to cope with environmental challenges. Animals react to aversive stimuli also through behavioral responses, defined as coping styles. Both in captive and wild populations, individuals differ in their behavior along a proactive-reactive continuum. Proactive animals exhibit a bold, active-explorative and social personality, whereas reactive ones are shy, less active-explorative and less social. Here, we test the hypothesis that personality traits and physiological responses to stressors covary, with more proactive individuals having a less pronounced GC stress response. In wild populations of invasive gray squirrels Sciurus carolinensis, we measured fecal glucocorticoid metabolites (FGMs), an integrated measure of circulating GCs, and 3 personality traits (activity, sociability, and exploration) derived from open field test (OFT) and mirror image stimulation (MIS) test. Gray squirrels had higher FGMs in Autumn than in Winter and males with scrotal testes had higher FGMs than nonbreeding males. Personality varied with body mass and population density. Squirrels expressed more activity-exploration at higher than at lower density and heavier squirrels had higher scores for activity-exploration than animals that weighed less. Variation in FGM concentrations was not correlated with the expression of the 3 personality traits. Hence, our results do not support a strong association between the behavioral and physiological stress responses but show that in wild populations, where animals experience varying environmental conditions, the GC endocrine response and the expression of personality are uncorrelated traits among individuals.

Interspecific competition affects the expression of personality-traits in natural populations.

Competition between animal species can cause niche partitioning and shape an individual's phenotype, including its behaviour. However, little is known about effects of interspecific competition on personality, the among-individual variation in behaviour that is consistent across different spatial and temporal contexts. We investigated whether alien grey squirrels (Sciurus carolinensis) influenced the expression of personality traits in native red squirrels (Sciurus vulgaris). In Italy, alien grey squirrels replaced native reds through competition for food resources and space, reducing breeding and recruitment in the native species. We compared personality of red squirrels in red-only (no interspecific competition) and red-grey (with interspecific competition) sites, using arena-tests. The trait activity was measured by Open Field Test while sociability and avoidance were quantified by Mirror Image Stimulation test. Red squirrels co-occurring with the alien species had higher sociability scores and higher between-individual variation in sociability than in red-only sites. Differences in activity and avoidance were not significant. Personality - fitness relationships were not affected by presence or absence of grey squirrels, suggesting that the expression of sociability in red squirrels was not due to short-term selection, but was likely the result of context-related advantages when co-occurring with the competing species.