Every organism on Earth is familiar with the price of life. Whether it be homeostasis, reproduction, or locomotion, everything that has to do with survival involves conservation of energy. All classes of animals face the problem of budgeting energy, but endotherms, especially mammals, face this issue with an already large portion of their energy budget dedicated to thermoregulation.
Therefore, it is imperative for mammals to adjust their behavior to account for energetically costly environmental and physiological demands. For example, how do mammals adjust their energy budget with changes in reproductive cycles and seasonal climate differences? Are there changes in the time of day when they are active, or how long they are active?
These were the questions asked in new work by Zhang and colleagues, who took advantage of new tracking technology to examine the timing of individual movement like never before. Using continuously-tracking accelerometer collars attached to North American stripped skunks (Mephitis mephitis), it was possible to track an individual’s daily activity, measured as overall dynamic body acceleration (ODBA), over several key time points throughout the year.
“One logistical challenge to understanding activity patterns in free-living mammals is that tools such as camera-trapping, live-trapping, and radio tracking, do not provide continuous information on an animal’s activity across the day and year”
Stripped skunks are nocturnal mesocarnivores that are naturally found in the ~5.5km study area located in Flagstaff, AZ. Zhang and colleagues tracked each individual’s ODBA’s over four device deployments that reflect changes in reproduction and seasonal climate: Winter (Nov 13—Dec 13), Mating season (Feb 29—Mar 22), Lactation/young at heel (Jun 26—Jul 22), and Fattening/young dispersal (Aug 18—Sept 18).
These samples were used to determine if there were differences in male/female activity and timing given the differences in physiological and environmental conditions skunks face throughout the year. The authors hypothesized that activity would reflect sex-specific differences in energy allocation towards reproduction and would be limited in adverse weather conditions such as low temperature, snow cover, or rain.
Their data did indeed show support for sex-specific differences in activity across seasons, but environmental conditions were only important in the winter, suggesting a primary role of reproduction in shaping daily activity in skunks. Males were the most active during the mating season, but females were the most active during lactating and fattening months.
There were also differences in the timing of activity bouts: Males had a relatively constant activity onset time throughout the year, resulting in a pattern where males start earlier and stay up later than females during mating, but the opposite pattern occurs during lactation, when females start earlier and stay up later.
Abiotic weather and temperature changes had little effect on ODBA patterns, excluding the winter when the presence of snow cover inhibited activity in both males in females. When rainfall was present activity onset was delayed and offset occurred earlier. Higher temperature and windspeed during warm months delayed cessation of activity.
These results illustrate that a combination of biotic and abiotic strains on the energy budgets of species can result in males and females differentially regulating their activity patterns throughout the year to balance their physiological needs. This study also demonstrates the success of using high-resolution accelerometers to record daily activity patterns of mammals, which were previously difficult to obtain.
This study leaves us with encouragement to use these newly available advanced tracking technologies to continue to understand energy tradeoffs in skunks and other animals, and to help us uncover other mysteries about what animals do when we’re not watching.
By William Ray and Emily Kane
William Ray is an Undergraduate Biology major at Georgia Southern University who is interested in wildlife biology and conservation. William has contributed to several research projects in the Kane Lab during his time at GSU, most notably as a volunteer on a pond recovery monitoring project.
Emily Kane is an Assistant Professor of Biology at Georgia Southern University. Her lab studies ecological and evolutionary biomechanics, mostly using fishes as model systems. Emily is also an advocate of outreach and science communication, incorporating these perspectives into both research and teaching.