Spatial ecology of moose in central Alaska: Movement behaviour, home range dynamics, and resource selection
Introduction
Moose (Alces alces) are a keystone species and ecosystem engineer in boreal and subarctic ecosystems, including Alaska, shaping ecosystems through bottom-up and top-down processes. They are prey for large carnivores, alter vegetation structure, nutrients and nitrogen cycles, as well as holding cultural and economic value through harvestings (Molvar, Bowyerm and Ballenberghe, 1993; Edenius et al., 2002; Pastor & Danell, 2003; Jennewein et al., 2020; Bowyer et al., 2026). Although stable worldwide (IUCN, 2015), southern populations of moose in North America are declining, mainly due to climate and landscape changes (Ditmer et al., 2018; Breithaupt et al., 2025). These changes are altering moose movement and home ranges, so understanding their space and resource use patterns per season can help inform conservation strategies. Central Akasa is useful to study these patterns as it is relatively undisturbed by human activity and has strong seasonal differences, so offers insight into natural habitat preferences (USDA NRCS, accessed 2026).
Moose spatial ecology, encompassing home range, movement and resource use, is shaped and varies with sexual dimorphism and seasonal demands (e.g., Dussault et al., 2005a; 2005b; Oehlers et al., 2011). Their high energetic demands mean they must maximise intake in Alaska’s short summers to build fat reserves to survive winter. Males have larger energetic needs due to their size and the rut in autumn, while females incur large winter fat losses due to lactating, while also having to considering their calves’ survival (Schwartz, 1992; Borowik et al., 2021; Thompson et al., 2024). These differences shape sex specific patterns, driven by energetic needs and resource availability, which vary seasonally across Alaska.
In Alaska, moose occupy a range of habitats, primarily using boreal forests dominated by conifers such as spruce (Picea mariana, Picea glauca), which provide cover from weather and predators. They also use areas with deciduous species, such as birch (Betula), which surround these forests, as well as shrubs like willow (Salix), found in wetland and riparian zones, which provide forage for moose (Shipley, 2010; Alaska Department of Fish and Game, 2015; Johnson & Rea, 2024; Breithaupt et al., 2025). Moose home ranges, traditionally defined as “that area traversed by an individual in its normal activities of food gathering, mating and caring for young” (Burt, 1943), represent resource use and the movement patterns linking resources across the land (Oehlers et al., 2011; Ofstad et al., 2019). As home range reflects a balance of resource uses, effective conservation strategies must consider resource needs and movement processes.
Plant availability varies seasonally. Summer provides abundant high quality nutritional forage, but is scarce and patchy in winter months, with willow being one of the few high quality plants available year round (Shipley, 2010). This drives high foraging rates in summer, enabling fat accumulation for winter, whilst also high rest rates in shaded areas to avoid heat stress (Jennewein et al., 2020). In winter, home ranges often expand, as individuals must travel further, but in short bursts due to snow constraints (e.g. Oehlers et al., 2011; Ditmer et al., 2018). Females are more likely to use high quality forage patches, wetlands and canopy cover to gain fat and protect their calves from predation (Dussault et al., 2005a; 2005b; Oehlers et al., 2011; Ofstad et al., 2019). Males are more likely to use lower elevations and prioritise quantity over quality in forage to meet their high energy needs, which reflects larger home ranges, particularly in winter when resources are scarce (Oehlers et al., 2011; Wattles and Destefano, 2013; Dorowik et al., 2021). As climate change raises temperatures, risk of heat stress intensifies so reliance on shade will increase and potentially reduce consumption in the summer. Understanding how sex and season influence movement and habitat selection is therefore needed to predict responses to environmental change (Ditmer et al., 2018; Jennewein et al., 2020).
Moose spatial ecology has been widely studied, yet research primarily focuses on female moose or rarely considers home range, resource use and movement behaviour simultaneously (e.g Dussault et al., 2005a; 2005b; Oehlers, et al., 2011 Thompson et al., 2024). To address this, the present study will investigate the impact of sex and season, integrating a multi-analytical approach across home range, behavioural movement, and resource use to provide a more comprehensive assessment of space use. This study has the following research questions:
How do home range sizes vary between winter and summer and between sexes?
Which habitats do moose select and avoid over a year?
How do behavioural states of moose vary between winter and summer, and does sex influence state use?
Methods
Study site
The moose in this study inhabit the upper Koyukuk River drainage in north central Alaska, within the Central Brook Range, including the Gates of the Arctic National Park and Preserve and the Kanuti National Wildlife Refuge. This region is characterised by boreal forests, wetlands and riparian zones and elevation ranges from lowland valleys to mountainous alpine regions. Human population is minimal apart from the Dalton Highway. This region is highly seasonal, with temperatures ranging from −40◦ C to 16◦ C (Joly et al., 2015A, 2015b; USDA NRCS accessed 2026). A full description of the study area is provided in Joly et al. (2015a, 2015b).
Data source
The telemetry data used in this analysis were obtained from Movebank (“Moose in Upper Koyukuk Alaska”), with 35 adult moose (22 female, 13 males) tracked via GPS collar from 17/03/2008 to 01/04/2013, yielding 71,675 fixes. Full details on deployment and data collection can be found in Joly et al. (2015a, 2015b).
Software
All statistical analysis were performed using RStudio with R version 4.5.2 (R Core Team, 2025).
Data processing
Data was cleaned in R Studio. Timestamps were converted to POSIXct format and locations were projected to UTM Zone 5N (EPSG:32605) to ensure spatial consistency. As a result, individuals with fixes outside of this zone were excluded, those with fewer than 11 out of zone fixes were retained once those points removed, as it had minimal impact on temporal structure. Fixes were recorded at 8 hour intervals, with individuals with only one fix a day removed to maintain consistency for the Hidden Markov Model (HMM). The package “move2” (Kranstauber, Safi, and Scharf, 2024) was used to identify outliers in time lags, speed, and distance. Most outliers were isolated ( <1% of fixes), so were retained to avoid creating long time gaps and subsequently, analytical methods capable of handling irregular data were used (Fleming et al., 2015; Silva et al., 2021). One individual with over 900 hours worth of time lags was removed as the data was not comparable.
The dataset was standardised to a year (15/04/2011 to 14/04/2012), containing 21,502 fixes from 21 individuals (Table 1). Two seasonal datasets were also created, with “summer” spanning 01/06/2011 to 31/08/2011 and “winter” running from 01/12/2011 to 29/02/2012 (Table 2 ).
Analysis and movement metric
Home range analysis
MCP
Home ranges were estimated using 95% minimum convex polygons (MCPs) per sex and season using “adehabitatHR” (Calenge, 2006). MCPs represent the smallest convex polygon enclosing 95% of GPS locations (Mohr, 1947). Although simple and widely used in home range research (e.g., Dussault et al., 2005a; Oehlers et al., 2011), they are sensitive to outliers and do not capture core areas. Subsequently, MCPs were used for exploratory comparison with Autocorrelated Kernel Density Estimation (AKDE) estimates.
AKDE
AKDEs 95% home ranges were estimates using “ctmm” (Calabrese, Fleming, and Gurarie, 2016; Fleming et al., 2019). AKDEs correct for autocorrelation and irregular sampling, so are less biased compared to traditional kernel methods (Fleming et al., 2015; Noonan et al., 2018; Silva et al., 2021).
Variograms were generated for each individual to assess range residency (Fleming et al., 2015; Silva et al., 2021), three individuals whose variograms indicated non-residency were removed from the analysis, leaving 18 animals investigated (8 female, 10 male). Seasonal AKDEs were conducted using pHREML after ctmm.guess was used to estimate starting movement parameters. Effective sample size (DOF) was also estimated to assess the reliability of home range estimates.
Resource use
RSF
Resource selection function (RSF) was used to investigate habitat use. RSF investigates locations, so are appropriate to use with coarse 8 hour fixes, which are unsuitable for fine-scale approaches such as step selection function (Thurfjell, Ciuti, Boyce, 2014; Avgar, et al., 2016).
A 30 m land cover raster, resampled to 120m, was used (MRLC, 2011). Within each MCP, ten available points were randomly generated for each used. Covariates included land cover class, patch area, patch isolation ( “landscapmetrics”) (Hesselbarth et al., 2019; Hollister, 2025). Habitats were categorised into ecological classes and variables standardised. An RSF was then fitted as a mixed effects logistic regression using “lme4” ( Millspaugh et al., 2006; Bates et al., 2015) with individual ID included as a random effect. A full year RSF was used here rather to capture annual habitat selection and identify a baseline for which habitats moose select or avoid more strongly.
Movement patterns and behavior
HMM
A two state Hidden Markov Model (HMM) was fitted separately for summer and winter using “momentuHMM” (McClintock and Michelot, 2018). Fixes over 8 hours capture broader behavioural states, states were classified as low and high movement states. Step length was modelled with a Gamma distribution and turning angle with a von Mises distribution. Sex and time of day were used as covariates to investigate differences in transitional probabilities. From step length and turning angles HMMs infer unobserved states and insight into movement strategies (Patterson et al., 2009; Leos-Barajas et al., 2017; McClintock and Michelot, 2018).
Results
Descriptives
A total of 21 adult moose (9 females, 12 males) were investigated following data cleaning (Table 1 and 2), of which 18 (8 females, 10 males) were investigated in the AKDE home range analysis.
| Sex | Number of Moose | Total Days Tracked | Average Days Tracked | Min Days Tracked | Max Days Tracked | Total Locations | Avg Locations | Min Locations | Max Locations |
|---|---|---|---|---|---|---|---|---|---|
| f | 9 | 365 | 363.89 | 362 | 365 | 9637 | 1071.00 | 1019 | 1091 |
| m | 12 | 364 | 361.58 | 356 | 364 | 11865 | 988.92 | 891 | 1085 |
| Season | Sex | Number of Moose | Total Days Tracked | Average Days Tracked | Min Days Tracked | Max Days Tracked | Total Locations | Avg Locations | Min Locations | Max Locations |
|---|---|---|---|---|---|---|---|---|---|---|
| summer | f | 9 | 92 | 92.00 | 92 | 92 | 2,413 | 268.1 | 246 | 276 |
| summer | m | 12 | 92 | 91.17 | 88 | 92 | 2,843 | 237.0 | 188 | 275 |
| winter | f | 9 | 91 | 90.78 | 89 | 91 | 2,430 | 270.0 | 265 | 273 |
| winter | m | 12 | 91 | 91.00 | 91 | 91 | 3,075 | 256.3 | 238 | 273 |
| Values represent tracking summaries by season and sex. The same 20 moose are monitored across both summer and winter |
Home range analysis
MCP
| sex | n | Mean Winter (95% MCP, km²) | SD Winter (km²) | Winter Min (km²) | Winter Max (km²) | Mean Summer (95% MCP, km²) | SD Summer (km²) | Summer Min (km²) | Summer Max (km²) |
|---|---|---|---|---|---|---|---|---|---|
| f | 8 | 59.0 | 50.7 | 4.4 | 163.5 | 88.9 | 54.1 | 20.5 | 192.5 |
| m | 10 | 114.3 | 88.2 | 44.9 | 325.1 | 100.1 | 67.0 | 25.4 | 251.1 |
A preliminary home range analysis was conducted using 95% MCPs. On average, female moose had smaller home ranges than males in both seasons. In winter females had smaller MCP home ranged (mean= 59 km², SD = 50.7 km² ) compared to males (mean = 114.3 km², SD = 88.2 km²). In summer, home ranges were closer in size, increasing for females to 88.9 km² (SD = 54.1 km² ), whilst males decreased to 100.1km² (± 67 km²SD).
AKDE
| season | sex | n | Mean 95% AKDE (km²) | Median 95% AKDE (km²) | SD 95% AKDE (km²) | Min 95% AKDE (km²) | Max 95% AKDE (km²) |
|---|---|---|---|---|---|---|---|
| summer | f | 8 | 258.3 | 148.9 | 264.4 | 31.9 | 747.0 |
| summer | m | 10 | 363.1 | 256.5 | 505.0 | 55.4 | 1760.9 |
| winter | f | 8 | 394.0 | 229.2 | 505.3 | 9.8 | 1535.6 |
| winter | m | 10 | 892.9 | 398.1 | 906.9 | 114.4 | 2577.6 |
Figure 1: Seasonal and sex differences in 95% AKDE home‑range area
Figure 2: Winter AKDE outputs
Figure 3: Summer AKDE outputs
Home range size varied between seasons and sexes (Table 4, Figure 1). Mean summer home range estimates using 95% AKDE was 363.1 km² for males, compared to females which were smaller, but less variable (mean = 258.3 km², SD = 264.4 km² ). Winter home ranges expanded for both sexes, with a mean of 892.9 km² for males and 394 km² for females. There was substantially greater variation amongst winter home ranges, particularly in the males (SD = 906.9 km²), with one home reaching 2577.6 km². Several winter home ranges had low effective sample sizes (DOF area = 1.2-4.9), indicating uncertainty due to temporal autocorrelation, whilst summer ranges had more constrained estimates (DOF area = 2–30).
Movement patterns and behavior
HMM
The two state HMM identified movement behaviours corresponding to low movement and high movement (Table 5).
| Parameter | Winter | Summer |
|---|---|---|
| Low Movement mean step (m) | 141.15 | 1135.19 |
| Low Movement SD (m) | 106.55 | 1151.84 |
| Low Movement zero-mass | 0.00 | 0.00 |
| High Movement mean step (m) | 714.17 | 205.59 |
| High Movement SD (m) | 659.82 | 183.31 |
| High Movement zero-mass | 0.00 | 0.00 |
| Angle concentration (Low Movement) | 0.38 | 0.26 |
| Angle concentration (High Movement) | 1.39 | 0.00 |
| Season | State | Count | Percent |
|---|---|---|---|
| Winter | 1 | 3888 | 70.4 |
| Winter | 2 | 1632 | 29.6 |
| Summer | 1 | 2986 | 56.4 |
| Summer | 2 | 2309 | 43.6 |
| Season | sex | state | n | percent |
|---|---|---|---|---|
| Winter | f | 1 | 1829 | 75.0 |
| Winter | f | 2 | 610 | 25.0 |
| Winter | m | 1 | 2059 | 66.8 |
| Winter | m | 2 | 1022 | 33.2 |
| Summer | f | 1 | 1623 | 66.4 |
| Summer | f | 2 | 822 | 33.6 |
| Summer | m | 1 | 1363 | 47.8 |
| Summer | m | 2 | 1487 | 52.2 |
Figure 4: Step length distribution in summer. High movement is displayed in red and low movement in blue.
Figure 5: Step length distribution in winter. High movement is displayed in blue and low movement in red.
The two state HMM identified movement behaviours corresponding to low movement and high movement (Table 5).
In summer, high movement was characterised by longer and more varied step length (mean = 1135.19 m, SD = 1151.84 ) and weak directionality (κ =0.26), whilst low movement showed shorter, consistent steps (mean = 205.59 m, SD = 183.21) and near-random turning (κ ≈ = 0). Moose were more likely to spend time in a high movement state (56.4%), with females more likely to occupy this state (66.4%), compared to males, who spent more time in lower movement states (52.2%). Males, however, showed a higher probability of switching from low to high movement (β =-0.78). Both states were highly persistent (>90% probability of remaining in the same state). Time of day was also included as a covariate, influencing transitioning behaviour with strong diel effects (–2.15 and +0.95). Including time of day and sex as covariates improved model fit (ΔAIC = 82), indicating that sex and the diel cycle influence movement state transitions.
The winter HMM similarly identified two movement states, with high movement characterised by longer step length (714.17 m, SD = 659.82) than low movement (141.15 m, SD = 1.06.55). High movement showed strong directionality (κ = 1.39), whilst low movement (κ = 0.38) showed weak directionality. Moose spent more time in low movement states (70.4%), particularly females (75%). States were persistent (>87% probability of remaining the same). Switching probabilities showed clear diel structure, with strong hour effects (–1.36 and +0.98). Including time of day and sex as covariates improved model fit (ΔAIC = 52.2), indicating that sex and the diel cycle influence movement state transitions.
Resource use
RSF
| Predictor | Estimate | Std. Error | z value | Pr(>|z|) |
|---|---|---|---|---|
| Intercept (grand mean habitat) | -2.330 | 0.136 | -17.159 | 0.000 |
| Patch area (scaled) | 0.203 | 0.014 | 14.404 | 0.000 |
| Isolation (scaled) | 0.035 | 0.006 | 5.915 | 0.000 |
| barren land | 0.015 | 0.296 | 0.051 | 0.959 |
| deciduous_forest | 0.849 | 0.189 | 4.493 | 0.000 |
| developed | -1.266 | 0.609 | -2.080 | 0.038 |
| evergreen_forest | 0.379 | 0.117 | 3.248 | 0.001 |
| herbaceous | -0.155 | 0.209 | -0.741 | 0.458 |
| mixed_forest | 0.603 | 0.159 | 3.788 | 0.000 |
| shrub | -0.220 | 0.156 | -1.417 | 0.157 |
| Model fitted with random slopes. |
Figure 6: Fixed effect coefficient for the mixed effect RSF
Overall, 216,170 used and 21,617 available locations were used in this RSF over 8 habitat categories. Shrub (n=156,985), evergreen (n=42,326), and deciduous forests (n= 13,053) were widely available, whereas the developed (n=215) habitat was the rarest.
A mixed effects RSF with random slopes and random intercepts was conducted; this showed singularity, and the random intercept was essentially zero, suggesting only the random slopes were meaningful. Therefore, a second mixed effects RSF was conducted with only random slopes. This RSF indicated significant differences in habitat selection (Table 8). Moose strongly selected to use deciduous forest (β = 0.849, p < 0.001), evergreen forest (β = 0.379, p = 0.001), and mixed forest habitats (β = 0.603, p < 0.001), whilst developed habitats were avoided (β = –1.266, p = 0.038), but due to limited locational numbers there was more variability here (SE = 0.609). Patch area also selected larger patches (β = 0.203, p < 0.001) but had a weak positive effect with patch isolation (β = 0.035, p < 0.001). This model also exhibited a singular fit, and model evaluation showed the model had a weak but meaningful discrimination between used and available points (AUC = 0.611).