The secret life of ground squirrels: accelerometry reveals sex-dependent plasticity in above-ground activity

Abstract

The sexes differ in how and when they allocate energy towards reproduction, but how this influences phenotypic plasticity in daily activity patterns is unclear. Here, we use collar-mounted light loggers and triaxial accelerometers to examine factors that affect time spent above ground and overall dynamic body acceleration (ODBA), an index of activity-specific energy expenditure, across the active season of free-living, semi-fossorial arctic ground squirrels (Urocitellus parryii). We found high day-to-day variability in time spent above ground and ODBA with most of the variance explained by environmental conditions known to affect thermal exchange. In both years, females spent more time below ground compared with males during parturition and early lactation; however, this difference was fourfold larger in the second year, possibly, because females were in better body condition. Daily ODBA positively correlated with time spent above ground in both sexes, but females were more active per unit time above ground. Consequently, daily ODBA did not differ between the sexes when females were early in lactation, even though females were above ground three to six fewer hours each day. Further, on top of having the additional burden of milk production, ODBA data indicate females also had fragmented rest patterns and were more active during late lactation. Our results indicate that sex differences in reproductive requirements can have a substantial influence on activity patterns, but the size of this effect may be dependent on capital resources accrued during gestation.

Day and night in the subterranean: measuring daily activity patterns of subterranean rodents (Ctenomys aff. knighti) using bio-logging

“…Light-logger recordings with values ≥2 lux were considered episodes on surface. Acceleration data were collected from the three orthogonal axes and used to calculate the overall dynamic body acceleration (ODBA) as described in Williams et al (2016). This method consists of subtracting the moving average from the data of each axis, using a 10-second time window.…”

Timing as a sexually selected trait: the right mate at the right moment

“…With the advent of technologies like biologging and tracking devices, we think that it is possible to address many of the open questions that we have outlined throughout this review in field populations-in birds, and especially also in mammals [141,144,177]. This will require long-term detailed behavioural studies to address how timing of display behaviour varies among individuals and how this variation relates to annual timing and reproductive success.…”

Estimating the energy expenditure of free‐ranging polar bears using tri‐axial accelerometers: A validation with doubly labeled water

“…Given their small size and external attachment, the use of accelerometers should reduce the potential for injury (Green, Haulena et al, 2009) and reduce the potential for influencing the animal's behavior and related energy expenditure (but see Chivers, Hatch, & Elliott, 2016;Maresh et al, 2014;Vandenabeele et al, 2014;Walker & Boveng, 1995;Wilson, 2011). As a result, DBA is increasingly being used as a proxy for energy expenditure in free-ranging animals (Bishop et al, 2015;Bryce, Wilmers, & Williams, 2017;Enstipp et al, 2016;Grémillet et al, 2018;Halsey & White, 2010;Hicks et al, 2018;Scharf, LaPoint, Wikelski, & Safi, 2016;Udyawer, Simpfendorfer, Heupel, & Clark, 2017;Wang, Smith, & Wilmers, 2017;Williams et al, 2016Wilmers et al, 2017;Wilson et al, 2012). However, DBA may underestimate changes in energy expenditure as a result of changes in basal metabolism, thermoregulation, specific dynamic action (heat increment of feeding), reproduction, or growth Green, Halsey et al, 2009;Halsey, Shepard et al, 2011;Figure 1).…”