The availability of thermal refuges shapes the thermoregulatory behavioural tactic of a heat-sensitive alpine endotherm species.

doi:10.21203/rs.3.rs-3923795/v1

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The availability of thermal refuges shapes the thermoregulatory behavioural tactic of a heat-sensitive alpine endotherm species.

https://doi.org/10.21203/rs.3.rs-3923795/v1

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With the ongoing rise in global average temperatures, animals are expected to increasingly dedicate their time and energy to thermoregulation. In response to high temperatures, animals typically either seek for and move into thermal refuges, or reduce their activity during the hottest hours of the day. Yet, the often lower resource availability in thermal refuges, combined with the reduction of foraging activity, may create indirect energetic costs of behavioural thermoregulation, forcing individuals to further adjust their behaviours under different spatial contexts. To elucidate such complex behavioural responses of individuals living in different landscapes, we studied how alpine chamois behaviour (Rupicapra rupicapra), a cold-adapted endotherm, varied in relation to both temperature and within-home range access to thermal refuges. We used Hidden Markov Models to analyse individual time-budgets and daily habitat use of 26 GPS-tagged females monitored during summer in the French Alps. Females showed heat stress avoidance behaviours above a threshold temperature of 17.8°C, increasing the use of forest and northern slopes by 2.8% and 2.2%, respectively, for each 1°C increase in temperature. Individuals with access to forests also increased daily time spent foraging, while individuals with access to northern slopes increased the time spent relocating at the expense of foraging. Including local landscape context and jointly analysing resource selection and behavioural activity is hence key for improved insights into nuanced changes in individual responses to climate change in different spatial contexts, providing also an improved evidence base for wildlife managers to identify and protect key thermal cover habitats.

climate change

activity budget

habitat use

heat stress

hidden Markov models

Global average surface temperature has increased by 0.95–1.20°C since the late 1800’s and is predicted to increase further by 1.5°C to 4°C by 2100 (IPCC, 2021), with critical consequences on ecosystem dynamics (Hoegh-Guldberg et al., 2018). Global warming affects plant distribution and phenology, as increasing temperature induces altitudinal/longitudinal shifts, shorter winters and earlier green-up and senescence (Cremonese et al., 2017; Vitasse et al., 2021). Such changes in vegetation can have cascading effects on herbivore species distributions (Brivio et al., 2019; Hamann et al., 2021) and population dynamics (Lovari et al., 2020; Reiner et al., 2021). In addition, in order to prevent heat stress (Speakman & Król, 2010), temperature rise may force individuals to dedicate an increasing part of their time and energy to thermoregulation (insects: Kellerman & Heerwarden, 2019; fish: Amat-Trigo et al., 2023; birds: Conradie et al., 2019; mammals: Brivio et al., 2016). To avoid costly and transient autonomic responses such as sweating (Maloney et al., 2005; Terrien et al., 2010), animals can buffer challenging thermal conditions through behavioural responses. This includes modifying their space use, such as relocating to thermal refuges, like forests, northern slopes, higher elevations, or shaded areas (Aublet et al., 2009; van Beest et al., 2012; Conradie et al., 2019; Marchand et al., 2015). Another strategy involves changing activity budgets, typically by reducing activity levels during the hottest hours of the day (Bourgoin et al., 2011; Brivio et al., 2016; Grignolio et al., 2018; Semenzato et al., 2021). However, behavioural thermoregulatory responses may come at a cost for the individual, as it can potentially impact resource acquisition and exposure to predation risk of individuals, with fitness consequences in the long term (Mysterud & Østbye, 1999; Mason et al., 2017, Conradie et al., 2019). For example, when temperatures increase, animals may decrease the time allocated to foraging, in particular in food-rich but thermally challenging open habitats (e.g. meadows, grasslands). This may lead individuals to display mitigation mechanisms in return, typically by increasing their foraging activity at dawn and dusk (e.g. Borowik et al., 2020; Semenzato et al. 2021), or during night-time (Grignolio et al., 2018). Such attempts to compensate during the cooler hours of the diel cycle for lost foraging opportunities during the hotter ones may be detrimental, for example by causing a higher exposure to nocturnal predators (Gehr et al., 2017, Brivio et al., 2024). Understanding how species cope with high temperatures then requires to go beyond the classical simple food acquisition versus predation risk avoidance trade-off (Mason et al., 2017), given that individuals have to cope also with additional thermoregulatory constraints (Herfindal et al., 2020). Investigating the role of thermoregulatory constraints is thus of crucial importance to evaluate the effects of global warming on population dynamics, as behavioural thermoregulatory tactics (altering habitat use, modifying allocation to different activities during hot hours, shifting to night-time activity) may directly impact energetic balance and in fine fitness (e.g. van Beest & Milner, 2013).

Mountain ecosystems are among areas where climate warming is particularly intense, making alpine species sentinels of the forthcoming effects expected elsewhere (Mason et al., 2014). Mountain ecosystems are also often viewed as a place of ‘nowhere to go’ (sensu Loarie et al. 2009 – i.e. there is a limit to how much species can continue to move up) when temperature rises and as such are considered to be more threatened than other ecosystems (Schmeller et al., 2022). However, the spatial gradient of temperature change is greater on mountain slopes, with small displacements in space resulting in a large temperature change (Loarie et al., 2009). This high degree of landscape heterogeneity leads individuals to experience very different biotic and abiotic conditions over very short distances, which can consequently drive individual differences in habitat selection and their ability to cope with ongoing rising temperatures (Duparc et al., 2019; Herfindal et al., 2020, Enriquez-Urzelai et al., 2020). Indeed, depending on the availability of suitable habitats for foraging, thermoregulating and escaping predation, individuals may adjust their space use or activity budgets differently to environmental constraints, displaying context-dependent behavioural responses. Such context-dependant responses in habitat selection (Mysterud & Ims, 1998; Holbrook et al., 2019) have been widely documented in large herbivores, particularly regarding the influence of food resources, predation refuges or fragmentation (“foodscape” and “landscape of fear”; Herfindal et al., 2009; Morellet et al., 2011; van Beest et al., 2016; Duparc et al., 2019; Seigle-Ferrand et al., 2022). Similar responses can be expected with the availability of thermal refuges (“thermal landscape”, e.g. van Beest et al., 2012; Verzuh et al., 2023). Investigating inter-individual variability in behavioural thermoregulatory responses is therefore essential, not only to identify thermal refuges, but also to better grasp the ability of individuals and populations with contrasted thermal landscapes to overcome the challenges posed by global warming.

Accordingly, we examined the impact of summer temperature on behavioural responses (habitat selection and activity budget) of GPS-tagged northern female chamois Rupicapra rupicapra, a cold-adapted species. During summer, female chamois require large amount of resources and energy to lactate (> 80% of adult females give birth few weeks before) and accumulate fat reserves for overwintering (Richard et al., 2017). Females are thus expected to dedicate a very important part or their time to foraging, exacerbating the trade-off between food acquisition and time spent in thermally challenging open grasslands (Marchand et al., 2015). We aimed to assess how fine-scale behavioural decisions (foraging, resting or relocating at 20-minute intervals) influence their activity budget (i.e. total daytime and night-time budget) and habitat selection based on current temperature and amount (% coverage) and type (north facing areas or forested areas) of shade available in their home range. We predicted that females with low access to thermal refuges, would be constrained to remain mostly in open areas when daily mean temperature increased (P1a), and would therefore respond to higher temperature by increasing the total time spent resting during daytime (P1b). This should lead to an increase in foraging and relocating time during dusk, night and dawn following hot-daytime temperatures, assuming that animals have to compensate for daytime foraging losses (P1c). Inversely, we predicted that individuals with higher access to thermal refuges, in terms of north facing areas and/or forest, would spend more time in shady habitats when temperature was high during daytime (P2a). The shift to these cooler habitats may buffer the impact of temperature on activity budgets and individuals may then show a lower increase in time spent resting compared to individuals with low access to thermal refuges (P2b), across all temperatures. If so, we expected a lower increase in time spent foraging and relocating during night-time for individuals with access to thermal refuges (P2c).

Study sites

We conducted our study in the Réserve Nationale de Chasse et de Faune Sauvage of Les Bauges Massif, in the northern French Alps (45°40′ N, 6°14′ E; 900 to 2200 m a.s.l., 5200 ha). We focused on two alpine areas (Charbonnet-Pleuven and Arménaz-Pécloz) 7 km distant from each other and separated by deep valleys with no exchange of individuals between them. Both areas were mostly covered with grasslands and rocky open areas and were comparable in terms of forest cover (mostly beech Fagus sylvatica and fir Abies alba, 18% and 25% of study sites’ areas, respectively), and north-oriented slopes (i.e. north and north east orientation, see the “Environmental characteristics” section; 11% and 17%, respectively; Lopez 2001).

The Reserve is inhabited by a chamois population of > 800 individuals (Maillard et al., 2014). In this population, the mean date of births is the first June and 80% of births occurred before 15 June (Loison, 1995). In our study area, chamois face limited natural predators, primarily golden eagles Aquila chrysaetos and red foxes Vulpes vulpes which may occasionally prey on newborn and injured animals. Additionally, the occasional presence of non-resident wolves Canis lupus has been noticed in some years during our study period (Loupfrance.fr, 2021).

GPS data

Data collection

Between 2014 to 2016, during July and August, 26 chamois adult females (2–17 years-old) were trapped with drop nets baited with artificial salt lick and equipped with GPS collars (Vectronics GPS Plus or Vectronics Vertex Plus) scheduled to record one location every 20 min from mid-July to mid-August (12th July-18th August in 2014; 11th July-17th August in 2015; 09th July-15th August in 2016) and one location every 4h during the rest of the year. Captures were performed according to the ethical conditions detailed in the specific accreditations delivered by the Préfecture de Paris (prefectorial decree n°2009-014) and in agreement with the French environmental code (Art. R421-15 to 421 − 31 and R422-92 to 422 − 94). As collar deployment and recovery occurred during summer, the total number of summer days with 20-min locations available per individual ranged between 6 and 38 days (median/mean = 16/19). We filtered out erroneous GPS locations (< 0.3% for both 20-min and 4h schedules) based on unlikely movement characteristics (Bjørneraas et al., 2010; Δ = 1500m, µ = 1000 m, α = 80% quantile of movement speeds from a focal individual, θ = −0·95).

Environmental characteristics

Temperature data

Local temperatures were recorded every 15 min at the Phenoclim weather station (CREA Mont-Blanc, creamontblanc.org) located in the Chérel mountain pastures (45°40' N, 6°12' E, 1380m above sea level and 2–8 km distant from the study areas). GPS locations of chamois were then matched with the corresponding temperature recorded at the same time or with the mean temperature of the two closest records. Daily mean temperatures ranged between 6.2°C and 22.8°C, with a mean of 15°C. Since the chamois inhabited higher elevation than the weather station (mean elevation of all GPS locations = 1810m a.s.l [1675m-1938m]_95%CI), we applied an adiabatic correction to our daily mean temperature records to model the expected temperatures at their mean elevation range. To achieve this, we subtracted a lapse rate of -0.65°C for each 100m elevation change between the weather station and the mean altitude of the chamois locations, which represented − 2.8°C for a 430m elevation change (Stone & Carlson, 1979). Corrected daily mean temperature therefore ranged between 3.4°C and 20°C, with a mean of 12.2°C.

GPS collars were also embedded with a sensor which recorded temperature at the same time as GPS locations. The ambient temperature experienced by chamois was derived from the temperature recorded by such sensors (hereafter named collar-ambient temperature) using the correction from Jiang et al. (2012) and a body temperature of animals equals to 39°C (Dematteis et al., 2008).

Characterization of thermal refuges

We distinguished three distinct habitat types offering contrasted thermal conditions. Habitat classification was based on the combination of a habitat map with a 25-m resolution (National Institute of Geographic and Forest Information) and an aspect map derived from a digital elevation model with a 25-m resolution (National Institute of Geographic and Forest Information, ign.fr). Forests (i.e. forests irrespective of the slope) and north-oriented slopes (i.e. unforested areas with a north and north east orientation, hereafter referred as “northern slopes”; between 337.5–360° and 0-67.5°; Bačkor, 2010; Anderwald et al., 2024), both considered as thermal refuges, and open habitats, i.e. areas without protection/shelter from high temperatures (i.e. without forests or north-oriented slopes). Indeed, during the hottest hours (between 12:00 to 16:00 UTC) of the hottest days (i.e. daily mean temperature > 17°C, 3rd quartile of temperature records), the temperature (as estimated from the collar sensors) in forest was on average − 1.2°C lower than in open habitats (range: -3.7 to 1.3°C, median: -1.5°C), despite a lower altitude of forests (mean altitude in forests = 1604m a.s.l; mean in open habitats = 1823m a.s.l.; based on GPS location of animals monitored), exemplifying the thermally challenging conditions encountered in grasslands. Similarly, the temperature in northern slopes was on average − 2.2°C lower than in open habitats (range: -6 to 0.8°C, median: -1.6°C), for a comparable altitude between both habitat types (mean northern slopes = 1860m a.s.l). While both forests and northern slopes provide shade, the use of forest implies using lower altitude areas (treeline approximately at 1600m in our study areas) so that the type of shade within an individual’s home range may lead to different responses to temperature in terms of habitat use and behaviour.

In addition, the availability of edible food resources also differed among the two types of thermal refuges and open habitats. In July and August, the mean edible biomass in open areas (July: 34g.m^− 2; August: 32g.m^− 2) was close to three times higher than in forest (July: 12g.m^− 2; August: 11g.m^− 2) and about one and a half times higher than in northern slopes (18g.m^− 2; August: 22 g.m^− 2; Duparc et al., 2020).

Estimation of access to thermal refuge in summer

We used 4h locations over the July-August period to estimate individuals’ summer utilization distribution, using the fixed-kernel method (Worton, 1989) with a smoothing parameter h set to the median value of individual smoothing parameters (h_individual=h_ref). We determined the summer home range at the 90% isopleth of utilization distribution, to obtain an unbiased estimate (Börger et al., 2006). We then determined the proportion of thermal refuges within individual summer home ranges and habitat types at chamois locations.

Statistical analyses

Determination of heat stress threshold

Considering that chamois may experience heat stress when the ambient temperature increases above a threshold, and may consequently exhibit thermoregulatory behaviour (Marchand et al., 2015; Semenzato et al., 2021), we estimated this temperature threshold. We used a segmented regression to analyse the relationship between collar-ambient temperature experienced by the animal and the study area-ambient temperature (recorded at the weather station and corrected for the difference of elevation with the study area inhabited by female chamois, see sub-section “Temperature data” in section “Environmental characteristics”).

Modelling of daily habitat use

To test whether individuals adjust their use of thermal refuges during hot days, we assessed how the proportions of total time spent in each of the three relevant habitat types (three response variables: open areas, forests and northern slopes) varied with corrected daily mean temperature recorded at the weather station and the percentage of forest and northern slopes available in the individuals’ home range, as well as their two-way interactions. We separated models for hottest (7 to 18 UTC, hereafter simplified as “daytime”) versus the cooler hours of the day (18 to 7 UTC, hereafter simplified as “night-time” although including twilight hours, Fig. 1), as we expected habitat use to be more affected by thermal refuges in home ranges during the hottest times of the day. We retained only days where 72 locations were recorded (median/mean = 12/17 days per individual). We used a mixed baseline-category logit model (“mblogit” function from R CRAN package “mclogit”, version 1.1–27.1, Bates et al., 2015) and included the identity of the individual as a random intercept. We then selected the most parsimonious model based on AIC criterion (Burnham & Anderson, 2002), retaining the one within a ΔAIC < 2 and with the smallest number of degrees of freedom.

Identifying behavioural states and modelling of daytime and night-time behavioural budgets

Following Beumer et al. (2020), we fitted Hidden Markov Models (HMMs) to the movement data of chamois (only location bursts with gaps < 6 consecutive locations; McClintock & Michelot, 2018), to identify the main behavioural states of chamois (see Appendices S2 to S5). We characterized three latent behavioural states approximating resting-ruminating (marked by very low speed and high spatial angles indicative of low directional persistence), foraging (with intermediate speed and angles), and relocating (marked by high speed and low spatial angle, indicative of directional persistence; Beumer et al., 2020; see also Appendices S4 & S5). This involved utilizing smoothed speed, achieved by averaging speed over the preceding two steps and the subsequent two steps for each location, and spatial angle computed at a constant step length (see details in Patin et al., 2018). We modelled smoothed speed and spatial angle with a gamma and a von Mises distribution, respectively. To determine whether individuals adjust their behaviours at the location scale in response to current environmental conditions, we fitted HMMs including temperature at the weather station, the habitat type at the individual’s current location (i.e. open habitat, forest or northern slopes, see Appendix S2), and the time of the location (20 min scale accounted as a circular variable) as covariates on the state distribution probabilities. Starting values of HMM were initialized by fitting 30 times a simple HMM without environmental covariates on state transitions probabilities, each time using a set of random starting values within a biologically relevant range based on observed chamois step length and turning angle distributions. We fitted all HMMs using momentuHMM R CRAN package (version 1.5.3, McClintock & Michelot, 2018). We selected the most parsimonious HMM, i.e. the one with a ΔAIC < 2 and the minimum number of transition probability coefficients, following a similar approach (based on the number of model parameters, Appendix S2) adopted by Clay et al. (2020). Finally, each GPS location was assigned to one of the three behavioural states using the Viterbi algorithm (“viterbi” function from “momentuHMM” package), and predicted values of stationary state probabilities (i.e. probability of being in a given state for each location depending on environmental covariates, Appendix S2 &S3) were derived from state transition probabilities using an adhoc function described by Clay et al. (2020).

Finally, we estimated the daytime and night-time proportions of time spent in the three behavioural states identified by HMMs. Then, we modelled these proportions separately (one set of models for daytime and another set for night-time proportions) with mixed baseline-category logit models, according to the daily mean temperature recorded at the weather station and its two-way interaction with the percentage of forest and the percentage of northern slopes available in the individuals’ home range. We followed the same model selection procedure as we described in section “Modelling of daily habitat use”.

Heat stress in northern chamois

We found a marked threshold-dependent relationship between collar-ambient temperatures and study area-ambient temperatures (Fig. 1A). The estimated threshold for this relationship was of 17.8°C. Below 17.8°C (95% CI = 17.5–18.2°C), collar-ambient temperatures increased by 0.77°C (95% CI = 0.75–0.78°C) per 1°C rise of the study area-ambient temperature, and by 0.17 (95% CI = 0.15–0.20°C) when temperature was above 17.8°C (Fig. 1A).

In addition, it is worth noting that on a “cool” day (daily mean temperature < 8°C), hourly temperature averages did not exceed 17.8°C during daytime, while on a “hot” day (daily mean temperature > 18°C) it exceeded this threshold for 8h on average, typically between 10 to 18 UTC (Fig. 1B). We may then consider in what follows, that animals experienced no heat stress when daily mean temperature of the study area was under 8°C, and strong heat stress when it exceeded 18°C.

Daily variation in habitat use in response to temperature and thermal refuges availability

Both during daytime and during night-time, the percentage of time spent in each habitat type varied with the study area’s daily mean temperature and the availability of thermal refuges in the home range (Table 1, see also Appendix S6). Both two-way interactions between temperature and availability of forest and northern slopes were retained in the best model for daytime, whereas only the two-way interaction between temperature and the availability of forest was retained for night-time (Table 1).

Table 1

Candidate mixed baseline-category logit models to investigate variation in daily habitat use (% of time spent in each habitat) in chamois, with individual identity as a random effect on the intercept. The best selected model is in bold. Temp = daily mean temperature; Forest = % of forest in home range; North.slop = % of northern slopes in home range.
Daytime models	df	AIC	delta	weight
Temp + Forest + North.slop + Forest:Temp + North.slop:Temp	15	17293.5	0	1
Temp + Forest + North.slop + North.slop:Temp	13	17316.4	22.85	0
Temp + Forest + North.slop + Forest:Temp	13	17321.4	27.89	0
Temp + North.slop + North.slop:Temp	11	17324.6	31.06	0
Temp + Forest + Forest:Temp	11	17336.4	42.9	0
Temp + Forest + North.slop	11	17379.8	86.21	0
Temp + Forest	9	17390.6	97.06	0
Temp + North.slop	9	17391.7	98.16	0
Temp	7	17402.9	109.37	0
Forest + North.slop	9	18046.4	752.81	0
Forest	7	18061.2	767.65	0
North.slop	7	18063.5	770	0
Null model	5	18072.2	778.65	0
Night-time models	df	AIC	delta	weight
Temp + Forest + North.slop + Forest:Temp	13	19957.1	0	0.671
Temp + Forest + North.slop + Forest:Temp + North.slop:Temp	15	19958.5	1.43	0.328
Temp + Forest + Forest:Temp	11	19970.9	13.84	0.001
Temp + Forest + North.slop + North.slop:Temp	13	20099	141.91	0
Temp + North.slop + North.slop:Temp	11	20101.7	144.59	0
Temp + North.slop	9	20206	248.93	0
Temp + Forest + North.slop	11	20206.3	249.27	0
Temp	7	20216.5	259.48	0
Temp + Forest	9	20219.8	262.78	0
Forest + North.slop	9	20581.8	624.72	0
North.slop	7	20583	625.97	0
Forest	7	20593.6	636.51	0
Null model	5	20594.4	637.3	0

As expected, female chamois which had low access to thermal refuges remained mainly in open areas during both daytime and night-time (Fig. 2A&D, support to P1a). Inversely, female chamois which had access to thermal refuges, decreased their use of open areas and increased their use of thermal refuges (i.e. forests or northern slopes) when daily mean temperature increased during daytime (support to P2a), but also to a lesser extent during the cooler hours of the day (dusk, night-time and dawn, Fig. 2). During daytime, individuals that had access to forests in their home range spent 28% more of their daily time in forests during hot days) compared to cool days (Figs. 2B). They also spent 9% more of their time in forests during the cooler hours of the day (Fig. 2E). Similarly, chamois with access to northern slopes increased their time spent in this thermal refuge by 22% during hot days compared to cool days (Fig. 2C), and by 7% during the cooler hours of the day (Fig. 2F).

Adjustments in daytime and night-time behavioural budgets to temperature and thermal refuges availability

Chamois dedicated the most important part of their daytime activity budget to foraging during both the coolest and hottest days (48–51% at 5°C, and 38–57% at 20°C, Fig. 3), followed by resting during the coolest days (25–34% at 5°C) or relocating during the hottest days (30–44% when at 20°C). During night-time, chamois dedicated most of their activity budget to resting (between 45–52% and 29–40% at 20°C) and foraging (35–39% at 5°C and 38–53% at 20°C, Fig. 3). During daytime, the proportion of time devoted to the three behavioural states varied with the study area’s daily mean temperature, the availability of forest and the availability of northern slopes in individuals’ home range, in an interactive way (Table 2, see also Appendix S7). Contrary to our predictions P1b and P2b, during daytime, time spent resting decreased for most individuals, and particularly for individuals with access to a large proportion of forests in their home range (Fig. 3A). Hence, when daily mean temperature increased from 8 to 18°C, chamois with low access to thermal refuges or mainly access to northern slopes, decreased their time spent resting by 7%, and 5% respectively, while chamois with access to forest decreased it by 15%. On the other side, time spent relocating increased with daily mean temperature for all individuals, i.e. by 7% in chamois with low access to thermal refuges, by 12% in those with access to northern slopes mostly, and by 9% in those with access to forest mostly (Fig. 3C). The variation in the proportion of daily time spent foraging with increasing temperature was more complex, as it increased by 5% for individuals with forest in their home range while it remained constant for individuals with low access to thermal refuge, and decreased by 7%, for individuals with access to northern slopes (Fig. 3B).

Table 2

Candidate mixed baseline-category logit models to investigate variation in activity budgets (% of time spent in each state) in chamois, with individual identity as a random effect on the intercept. The best selected model is in bold. Temp = daily mean temperature; Forest = % of forest in home range; North.slop = % of northern slopes in home range.
Models	df	AIC	ΔAIC	weight
Temp + Forest + North.slop + Forest:Temp + North.slop:Temp	15	33125.1	0	0.922
Temp + Forest + North.slop + Forest:Temp	13	33130.3	5.21	0.068
Temp + Forest + Forest:Temp	11	33134.9	9.86	0.007
Temp + North.slop + North.slop:Temp	11	33136.7	11.69	0.003
Temp + Forest + North.slop + North.slop:Temp	13	33138.9	13.89	0.001
Temp + North.slop	9	33156.4	31.37	0
Temp + Forest	9	33158.3	33.26	0
Temp + Forest + North.slop	11	33158.7	33.64	0
Temp	7	33163.1	38.07	0
North.slop	7	33299.4	174.33	0
Forest + North.slop	9	33302.5	177.43	0
Forest	7	33302.9	177.83	0
Null model	5	33305.8	180.78	0
Night-time models	df	AIC	ΔAIC	weight
Temp + Forest + North.slop + Forest:Temp + North.slop:Temp	15	60900.5	0	0.996
Temp + Forest + Forest:Temp	11	60911.6	11.13	0.004
Temp + Forest + North.slop + Forest:Temp	13	60916	15.52	0
Temp + North.slop + North.slop:Temp	11	60933.2	32.73	0
Temp + Forest + North.slop + North.slop:Temp	13	60936.2	35.68	0
Temp	7	60949.5	49.05	0
Temp + Forest	9	60953	52.52	0
Temp + North.slop	9	60954.4	53.9	0
Temp + Forest + North.slop	11	60957.4	56.88	0
Null model	5	61110.7	210.22	0
Forest	7	61113.7	213.24	0
North.slop	7	61114.1	213.56	0
Forest + North.slop	9	61120.4	219.93	0

During night-time, the proportion of time devoted to the three behavioural states varied with the study area’s daily mean temperature, the availability of forest and the availability of northern slopes in individuals’ home range, in an interactive way (Table 2). In accordance with our prediction P1c, during night-time following hot daytime temperatures, time spent resting decreased in individuals with low access to thermal refuges. However, contrary to our prediction P2c, individuals with access to thermal refuges, and in particular in individuals with access to forest, showed an even higher decrease in time spent resting (Fig. 3D). When daily mean temperature increased from 8 to 18°C, chamois with low access to thermal refuges or mainly access to northern slopes, decreased their time spent resting by 4%, and 7% respectively, while chamois with access to forest decreased it by 15%. Inversely, time spent relocating increased by 2% and 3% in individuals with low access to thermal refuges or access to forest, and up to 7% for individuals with access to northern slopes (Fig. 3F). The variation in the proportion of time spent foraging with increasing temperature was the same as the daytime response, as it increased by 12% for individuals with forest in their home range, while it remained constant for individuals with low access to thermal refuge and with access to northern slopes mostly (Fig. 3E).

We showed how female chamois fine-tuned their response to hot summer temperatures by adjusting their habitat use and activity budget in ways that depended on the spatial context, i.e. individual’s within-home range thermal landscape. More specifically, females showed signs of thermoregulatory behaviours in response to heat stress above a threshold temperature of c.a. 18°C. Individuals with access to forest increased their daily time spent foraging there, while individuals with access to northern slopes increased the time spent relocating at the expense of foraging. This thermoregulatory behaviour can be interpreted as a context-dependant response (Mysterud and Ims, 1998) to temperature, as individual responses depend on individual exposure to temperature and opportunities to escape heat. Responses to temperature can hence be complex and even counterintuitive (e.g. an increase in time spent relocating with increasing temperature, see explanations below), when both changes in habitat selection and time allocated to different activities can be modified as mitigation measures. Below, we discuss in detail how individuals’ access to thermal refuge generates inter-individual variability in their behavioural responses to increasing temperatures and how this could impact the energy budget, demography and spatial distribution of this cold-adapted mountain herbivore.

Relocating into thermal refuges under high summer temperatures is a commonly documented behaviour in large herbivores (moose: van Beest et al., 2012; ibex: Semenzato et al., 2021; mouflon: Marchand et al., 2015). In Alpine ibex and Mediterranean mouflon, such a thermoregulatory behaviour has been found to occur above the values of 13–14°C and 15–17°C, respectively (Aublet et al., 2009; Marchand et al., 2015; Semenzato et al., 2021), i.e. threshold temperatures similar to the one reported here for female chamois (Fig. 1A; 18°C). Above this threshold, the capacity of female chamois to dissipate heat was probably reached (heat dissipation limit hypothesis; Terrien et al., 2011) leading animals to adjust their behaviour to avoid the detrimental effects of hyperthermia. In our study, females exhibited behavioural adjustments that enabled them to maintain their surrounding temperature within the thresholds controlling thermoregulation even as the temperature continued to rise beyond this limit (Fig. 1A). This probably illustrates how the marked spatial gradient of temperature in mountains allows animals through limited daily displacements to keep pace with the rate of temperature changes - in contrast to flatter areas where large geographic displacements are required to change temperature appreciably (Hopkins, 1920; Loarie et al., 2009). These behavioural responses may however incur costs in terms of energy acquisition and behavioural budgets, as behavioural thermoregulation often trades-off against foraging (e.g. see Cunningham et al., 2021 for a review in mammals and birds). In cold-adapted ungulate species for example, relocating in thermal refuges may typically provide decreased foraging conditions (e.g. in moose: Alston et al., 2020; Street et al., 2016; van Beest et al., 2012, and in ibex: Mason et al., 2017; Semenzato et al., 2021). Likewise, when possible, chamois decreased their daily time spent in open habitats in favour of thermal refuges, i.e. forest and northern slopes, when daily mean temperatures increased, while forage quality and quantity are up to three times higher in open habitats than in forest or northern slopes (Duparc et al., 2020; see also Methods). Thus, moving into thermal refuges may incur indirect energetic costs due to reduced foraging conditions, if no behavioural adjustments are made by individuals to alleviate the latter.

Chamois showed such behavioural adjustments by increasing their relocating activity and exhibiting a more contrasted response in foraging activity. Importantly, we showed that the availability of thermal refuges in individual home ranges had an important influence on individual responses to high temperatures. Thermal refuges availability indeed first shaped a context-dependant response in habitat use in chamois females. Individuals increased their use of thermal refuges when those were more abundant. Even more importantly, we also showed a context-dependant response in behavioural budget adjustments. Depending on the type and availability of thermal refuges, individuals allocated time differently to each behaviour. The increase in time spent relocating during the cool hours of the day when daytime temperature increased, especially for chamois with access to forest, was unexpected. However, it could be a consequence of the reduced time spent in rich open habitats during daytime. Compensation mechanisms have been observed in other large herbivore species, typically by shifting a part of their daytime activity to night-time (Grignolio et al., 2018; Borowik et al., 2020; Semenzato et al., 2021). Here, increased activity during night-time may correspond to individuals travelling back from thermal refuges to open areas, where they may then spend more time looking for food items inside of patches, i.e. foraging activity, or visiting more food patches during relocating activity, in order to mitigate the opportunity costs (such as missed foraging opportunities linked to decreased forage quantity, Cunningham et al., 2021) of moving into thermal refuges during daytime. Conversely, and in line with the increased use of forest areas for individuals with forests within home ranges (Fig. 2D, E), the increased activity may be related to different food distributions within forests.

Accordingly, in addition to shifting their daytime activity to night-time, it is more likely that individuals did also try to mitigate opportunity costs once they were in thermal refuges during daytime. The reduced quantity of forage in forests for example may explain the increased propensity of chamois to forage when there, which lead individuals to increase their time spent foraging during the hottest days, especially during daytime (Fig. 3). Similarly, chamois in areas with northern slopes showed an increased propensity to relocate during the hottest days, in accordance with the hypothesis that the reduced forage availability and quality in northern slopes (Duparc et al., 2020) requires chamois to spend more time searching for and visiting food patches, and commute between areas in the shade and food patches.

Behavioural thermoregulation may induce direct energetic costs for individuals, as increased time spent relocating towards and within thermal refuges, may lead to increased distances travelled and cumulated elevation change, which in return is likely to yield increased movement costs (Wilson et al., 2020). Previous studies have demonstrated that ungulates respond to the combined influence of risk/disturbance distribution and foodscape in landscapes, in agreement with the classical food acquisition/risk avoidance trade-off (e.g. roe deer: Benoit et al., 2023; chamois: Courbin et al., 2022). For example, Courbin et al. (2022) demonstrated an increased daily displacement of chamois during summer as a response of hiker presence (see also Thel et al., 2023 on activity budget). The highest temperature occurs when (day time) and where (open areas) disturbance is highest, which may have synergetic consequences on mountain ungulate behaviour, and if repeated, cumulative effects affecting fitness. In addition, the return of large carnivores in European mountains (Chapron et al., 2014; Cimatti et al., 2022), which are mostly nocturnal, may alter the compensatory foraging response of animals during the night.

To conclude, we showed in this study that behavioural thermoregulation may incur opportunity costs for chamois during summer, and that these costs may be modulated by the local thermal landscape characteristics experienced by individuals. Importantly, for wildlife management and conservation this means that management plans and policies cannot be applied uniformly across managed areas, but may need to consider the finer scale local spatial context. In a context of more frequent heat waves and droughts due to global warming (IPCC, 2021), it is then most likely that these costs will keep increasing, and this might constitute quite an important issue for the conservation of cold-adapted species. As other capital breeders (Arnold, 2020), chamois rely on fat reserves accumulated during spring and summer to face winter food scarcity and the energetic costs of gestation and lactation (Richard et al., 2017). Changes in foraging efficiency linked to behavioural thermoregulation may then lead to potential changes in energy acquisition and related offspring maternal care (e.g. Scornavacca et al., 2016). Consequently, further work will be needed to determine whether the diverse costs of behavioural thermoregulation (i.e. decreased forage quality and quantity, lost foraging opportunities, increase in costly movements for relocations), may become detrimental for survival individuals and population dynamics, if we aim to assess the vulnerability of chamois population to climate change.

Author’s contribution

AM, AL and LB originally formulated the idea, and conceived the study. AM analyzed the data, and led the writing of the manuscript. All authors, i.e. AM, AL, LB, NB, NC, NM, MG and PM significantly contributed to the writing of the manuscript.

Acknowledgments

We thank all our colleagues from the Mov-It group for our fruitful discussions. We also thank all volunteers and professionals from the Office Français de la Biodiversité for helping with the capture and marking of animals, and for the recovery of GPS collars. We are grateful as well to the CREA Mont-Blanc for providing us the temperature data. Alexis Malagnino would also like to warmly thank William Kay for his help with the understanding and handling of hidden Markov Models.

Funding

This work was funded by the Université Grenoble Alpes & Swansea University, and conceived and written within the ANR Mov-It project (ANR #16-CE02-0010).

Conflict of Interest: The authors declare that they have no conflict of interest.

Ethical Approval: All applicable institutional and/or national guidelines for the care and use of animals were followed.

Consent to participate: Not applicable.

Consent for publication: Not applicable.

Availability of data and material: The datasets used and analysed during the current study are available from the corresponding author on reasonable request.

Code availability: The code scripts used during the current study are available from the corresponding author on reasonable request.

Author’s contribution

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The availability of thermal refuges shapes the thermoregulatory behavioural tactic of a heat-sensitive alpine endotherm species.

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Abstract

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Introduction

Methods

Study sites

GPS data

Data collection

Environmental characteristics

Temperature data

Characterization of thermal refuges

Estimation of access to thermal refuge in summer

Statistical analyses

Determination of heat stress threshold

Modelling of daily habitat use

Identifying behavioural states and modelling of daytime and night-time behavioural budgets

Results

Heat stress in northern chamois

Daily variation in habitat use in response to temperature and thermal refuges availability

Adjustments in daytime and night-time behavioural budgets to temperature and thermal refuges availability

Discussion

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References

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