1. Organisms survive environmental variation by combining homeostatic regulation of critical states with allostatic variation of other traits, and species differences in these responses can contribute to coexistence in temporally-variable environments.
2. In this paper, we simultaneously record variation in three functional traits – body temperature (Tb), heart rate, and activity - in relation to three forms of environmental variation – air temperature (Ta), photoperiod, and experimentally-manipulated resource levels – in free-ranging snowshoe hares and North American red squirrels to characterize distinctions in homeotherm responses to the extreme conditions of northern boreal winters.
3. Hares and squirrels differed in the level and precision of Tb regulation, but also in the allostatic pathways necessary to maintain thermal homeostasis. Hares demonstrated a stronger metabolic pathway (through heart rate variation reflective of the thermogenesis), while squirrels demonstrated a stronger behavioral pathway (through activity variation that minimizes cold exposure).
4. As intermediate-sized, winter-active homeotherms, hares and squirrels share many functional attributes, yet, through the integrated monitoring of multiple functional traits in response to shared environmental variation, our study reveals many pairwise species differences in homeostatic and allostatic traits, that both define and are defined by the natural history, functional niches, and coexistence of sympatric species.

Heart rate and body temperature readings were collected every 10 minutes with implantable dataloggers (surgically implanted in the abdomen). Values in the datasheet (HeartRate_Tb_Data.csv) represent averages for a given behavioural state (active vs. inactive or in the nest), for each phase of the day (dawn, dusk, day, night), for each individual. 

Activity data was recorded via accelerometers set a 1Hz; acceleration across the three axes was recorded once per. Behavioural states were determined through species-specific hierarchical decision trees. The proportion of each phase spent active (Prop_Active in Activity_Data.csv) was calculated by dividing the number of seconds spent active (for squirrels = out of the nest; for hares = foraging, hopping and sprinting) by the duration of each phase (in seconds). 

Air temperature was recorded once every 30 minutes across 3 sites; the value presented in the datasheets is the average air temperature across all 3 sites, for the time periods when heart rate, body temperature and activity recordings were taken. 
 

HeartRate_Tb_Data.csv
Columns:
Species: identifies either red squirrel (Squirrel) or snowshoe hare (Hare)
ID: the individual ID of a given squirrel and/or hare
FieldSeason: whether data was collected during winter 2016 (2015-2016) or winter 2017 (2016-2017)
Date: date that the recordings were taken (in YYYY-MM-DD format)
Phase: phase of the day (Day, Night, Dawn, Dusk)
BehavioralState: whether a squirrel was in the nest (Nest) or out of the nest (Out); or, whether a hare was resting (Rest) or active (Active) 
Food: experimental food supplementation status (Food vs. Control)
Mass: body mass of the animal (in g)
Tb: body temperature (in ^oC)
HR: heart rate (in beats per minute)
Ta: air temperature (in ^oC)

Activity_Data.csv
Columns:
Species: identifies either red squirrel (Squirrel) or snowshoe hare (Hare)
ID: the individual ID of a given squirrel and/or hare
FieldSeason: whether data was collected during winter 2016 (2015-2016) or winter 2017 (2016-2017)
Date: date that the recordings were taken (in YYYY-MM-DD format)
Phase: phase of the day (Day, Night, Dawn, Dusk)
Food: experimental food supplementation status (Food vs. Control)
Mass: body mass of the animal (in g)
Prop_Inactive: the proportion of each phase spent inactive
Prop_Active: the proportion of each phase spent active
Ta: air temperature (in ^oC)